Asme b31 3 code case 181 2 flaw evaluation worksheet rev01 by Charlie Chong

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

CC 181-2, Section 8 Flaw Evaluation Worksheets Sridhar Samiyaiah/ Charlie Chong

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

PAUT Interpretation to ANSI B31.3before re-testing and before shipment.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Phased Array Flaw Sizing Using the OmniScan MX2 Phased array flaw depth and height sizing requires both a knowledge of the application and use of the tools in the software. This Webinar is intended to take the participant through the basics of phased array depth and height flaw sizing with real world examples by expanding on traditional conventional techniques with advanced phased array probes and software. Shear wave tip diffraction, -6dB sizing, high angle longitudinal L-wave, ID Creeping wave, and other advanced techniques will be on display. . Additionally, use of the OmniSscan measurement cursors, defect table and report are explained and demonstrated. Also on display will be Olympus' new software "OmniPC" for computer based offline analysis of OmniScan data files

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https://www.youtube.com/embed/hRm6K3ryrFY

OmniScan MX2 Training Program Part 1 /2/3/4

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https://www.youtube.com/watch?v=Z-z7ue6i6FQ&t=835s

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Foreword; The purpose of performing RT/UT or PAUT is to evaluate the entire volume of a weld for the detection of potentially detrimental discontinuities in a weld in accordance with written procedures, guidelines, standards and codes. ASME B31.3 contains code requirements for piping typically found in petroleum refineries, as well as chemical, pharmaceutical and other related processing plants and terminals. Successful applications of NDT methods including PAUT can help the project to achieve operational, cost and safety benefits by implementing the best industry practices.

Sridhar Samiyaiah

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

What is Code Case 181-2?

Rosafendi/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3 Original Inquiry: Under what conditions and limitations may alternative UT acceptance criteria apply in lieu of those described in para. 344.6.2 of ASME B31.3?

Keywords: may alternative UT acceptance criteria

Comments: CC 181-2, it was meant for alternative to UT not RT Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

What is the Alternative?

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Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3 Original Inquiry: Under what conditions and limitations may alternative UT acceptance criteria apply in lieu of those described in para. 344.6.2 of ASME B31.3?

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Para. 344.6.2 of ASME B31.3

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Alternative to Para. 344.6.2 of ASME B31.3

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

What is ASME ANSI B31.3 para 344.6.2, the “original”?

Rosafendi/ Charlie Chong

344.6 Ultrasonic Examination 344.6.2 Acceptance Criteria. A linear-type discontinuity is unacceptable if the amplitude of the indication exceeds the reference level and its length exceeds (a) 6 mm (1⁄4 in.) for Tw ≤ 19 mm (3⁄4 in.) (b) Tw/3 for 19 mm < Tw ≤ 57 mm (21⁄4 in.) (c) 19 mm for Tw > 57 mm

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B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Why there is a need for alternative to the ASME ANSI B31.3 para 344.6.2, the â&#x20AC;&#x153;originalâ&#x20AC;??

Rosafendi/ Charlie Chong

Hipressure (Mechanical) (OP) 7 Jun 07 19:05 B31 CC 181 I am trying to understand this case; is it one of alternative acceptance criteria or is it alternative technique? We are trying to employ PAUT on 31.3 piping using the given acceptance criteria for UT in 31.3. However this code case was brought up in discussions and it was determined that if PAUT was to be used, this CC (including acceptance criteria) had to be followed in its entirety. Greatly appreciate any and all comments and/or interpretations on this CC. Regards RE: B31 CC 181 ndeguy (Industrial) 7 Jun 07 23:43 Its definitely about both! The preeamble states that the Committee is of the opinion that alternative acceptance criteria can be applied in lieu 0f 344.6.2. of B31.3. This is a switch from acceptance criteria based on comparison with the amplitude from known reflectors to the measured defect height (versus its length and material thickness). Plus (d) of the Code Case calls for use of a device employing "automatic computer-based data acquisition". Interesting if unusual point about using phased array with the standard acceptance criteria. Without doing the math comparison for various material thicknesses it is generally accepted that the alternative acceptance criteria, which are based on materials and stress data rather than traditional "workmanship" values, are more lenient, especially in the case of low defect height versus material thickness ratios, e.g. inter-run cold lap. Exceptions to this can be in cases of several separate defects where interaction rules are invoked - think of automatic MIG pipewelding systems such as Phoenix or Serimer where the sequential fire-up positions are not staggered and a small length of LOF (10 mm say) is in each successive vertical position. These are interactive and such fire-up defects in 3 or 4 successive runs would give an unacceptable interactive defect height. Which welding process(es) will you be utilising? If all manual (TIG root/SMAW fill and cap) I dont know why you could not set your PAUT sensitivity using the standard ASME calibration block assessing defect length for reference-curve breaking indications. Nigel Armstrong Karachaganak Petroleum Kazakhstan

Sridhar Samiyaiah/ Charlie Chong

http://www.eng-tips.com/viewthread.cfm?qid=189121

traditional "workmanship" values, are

more lenient

, especially in the case of low defect height

versus material thickness ratios, e.g. inter-run cold lap. Exceptions to this can be in cases of several separate defects where interaction rules are invoked - think of automatic MIG pipe-welding systems such as Phoenix or Serimer where the sequential fire-up positions are not staggered and a small length of LOF (10 mm say) is in each successive vertical position. These are interactive and such fire-up defects in 3 or 4 successive runs would give an unacceptable interactive defect height. Which welding process(es) will you be utilising? If all manual (TIG root/SMAW fill and cap) I dont know why you could not set your PAUT sensitivity using the standard ASME calibration block assessing defect length for reference-curve breaking indications. Nigel Armstrong Karachaganak Petroleum Kazakhstan Sridhar Samiyaiah/ Charlie Chong

http://www.eng-tips.com/viewthread.cfm?qid=189121

How to decide a indication whether is acceptable or rejectable?

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CC181-2 ANSI B31.1 Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

7) Flaw Evaluation a) The dimension of the flaw(s) shall be determined by the rectangle that fully contains the area of the flaw(s). (Refer to Fig. 1) i)

The length, â&#x201E;&#x201C;, of the flaw shall be drawn parallel to the inside pressure retaining surface of the component. ii) The height, h, of the flaw shall be drawn normal to the inside pressure retaining surface of the component. iii) The flaw shall be characterized as a surface or subsurface flaw, as shown in Figure 1. iv) A subsurface indication shall be considered as a surface flaw if the separation (S in Figure 1) of the indication from the nearest surface of the component is equal to or less than half the through wall dimension (h in Figure 1, sketch [b]) of the subsurface indication.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

How to define an indication dimension?

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The length, ℓ, of the flaw shall be drawn parallel to the inside pressure retaining surface of the component.

ℓ

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B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

ii.

The height, h, of the flaw shall be drawn normal to the inside pressure retaining surface of the component.

h h

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

How to ascertain an indication is surface or subsurface?

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iii. The flaw shall be characterized as a surface or subsurface flaw, as shown in Figure 1.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

iv. A subsurface indication shall be considered as a surface flaw if the separation (S in Figure 1) of the indication from the nearest surface of the component is equal to or less than half the through wall dimension (h in Figure 1, sketch [b]) of the subsurface indication.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Exercise: Surface or Subsurface? S>0.5h or ≤ 0.5h ? ℓ = 30mm

t = 40mm

h = 10mm S = 7mm

ℓ = 30mm Sridhar Samiyaiah/ Charlie Chong

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Exercise: Surface or Subsurface? S>0.5h or ≤ 0.5h ?

ℓ = 30mm

60mm

h = 10mm S = 7mm

ℓ = 30mm Sridhar Samiyaiah/ Charlie Chong

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

How to define 2 or more adjacent indications to be a single flaw or separate flaws?

Rosafendi/ Charlie Chong

b) Multiple Flaws i) Discontinuous flaws that are oriented primarily in parallel planes shall be considered to lie in a single plane if the distance between the adjacent planes is equal to or less than 13mm (0.50 in.) or 0.5t, whichever is less. ii) If the space between two flaws aligned along the axis of weld is less than the height of the flaw of greater height, the two flaws shall be considered a single flaw. iii) If the space between two flaws aligned in the through-thickness dimension is less than the height of the flaw of greater height, the two flaws shall be considered a single flaw.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Discontinuous flaws that are oriented primarily in parallel planes shall be considered to lie in a single plane if the distance between the adjacent planes is equal to or less than 13mm (0.50 in.) or 0.5t, whichever is less.

distance between the adjacent planes

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

ii) If the space between two flaws aligned along the axis of weld is less than the height of the flaw of greater height, the two flaws shall be considered a single flaw.

d =space between two flaws aligned along the axis of weld

h1 h3

Cross Section X-X Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

iii) If the space between two flaws aligned in the through-thickness dimension is less than the height of the flaw of greater height, the two flaws shall be considered a single flaw.

h1 h3

through-thickness dimension

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

iii) If the space between two flaws aligned in the through-thickness dimension is less than the height of the flaw of greater height, the two flaws shall be considered a single flaw.

h1 h3

t h2

through-thickness dimension

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

How to decide whether a flaw is “Acceptable” or “Rejectable”?

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8) Flaw Acceptance Criteria Flaws shall be evaluated against the applicable acceptance criteria of Table 1 or 2, except that flaw length (l) shall not exceed 4t, regardless of flaw height (h) or the calculated aspect ratio.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Comments: flaw length (l) shall not exceed 4t

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Comments: flaw length (l) shall not exceed 4t

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

flaw length (l) shall not exceed 4t t = thickness of the weld excluding any allowable reinforcement. For a butt joint joining two members having different thickness at the joint, t is the thinner of the two thicknesses joined. If a full penetration weld includes a fillet weld, the effective throat dimension of the fillet weld shall be included in t.

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

What is “t” ?

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thickness of the weld excluding any allowable reinforcement. For a butt joint joining two members having different thickness at the joint, t is the thinner of the two thicknesses joined. If a full penetration weld includes a fillet weld, the effective throat dimension of the fillet weld shall be included in t.

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Sridhar Samiyaiah/ Charlie Chong

B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

The CC181-2 Acceptance Criteria Table.

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TABLE 1 Acceptance Criteria for Surface Flaws

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

General Notes: (a) t = thickness of the weld excluding any allowable reinforcement. For a butt joint joining two members having different thickness at the joint, t is the thinner of the two thicknesses joined. If a full penetration weld includes a fillet weld, the effective throat dimension of the fillet weld shall be included in t. (b) Aspect Ratio (h/ℓ) used may be determined by rounding the calculated h/ℓ down to the nearest 0.05 increment value within the column, or by linear interpolation. (c) For intermediate thickness t (weld thicknesses between 64mm and 100mm [2.5 in. and 3.9 in.]) linear interpolation is required to obtain h/t values.

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B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

TABLE 2 Acceptance Criteria for Subsurface Flaws

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B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

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B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

Of B31 Case 181â&#x20AC;?2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

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Time for Practice.

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Sridhar Samiyaiah/ Charlie Chong

CC 181-2 Table1 & Table 2 Aspect Ratio h/â&#x201E;&#x201C;

25~64mm

100~300mm

25~64mm

100~300mm

0.0

0.031

0.019

0.068

0.04

0.05

0.033

0.02

0.1

0.036

0.022

0.076

0.044

0.15

0.041

0.025

0.2

0.047

0.028

0.086

0.05

0.25

0.055

0.033

0.3

0.064

0.038

0.098

0.058

0.35

0.074

0.044

0.4

0.083

0.05

0.114

0.066

0.45

0.085

0.051

0.5

0.087

0.052

0.132

0.066

0.6

0.156

0.088

0.7

0.18

0.102

0.8

0.21

0.116

0.9

0.246

0.134

1.0

0.286

0.152

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Surface h/t

Sub-Surface h/t

CASE STUDY #1 ℓ = 30mm h= 10mm S = 7mm t = 40mm

Aspect Ratio h/ℓ

25~64mm

0.3

0.098

Sub-Surface h/t

0.35

0.10328

0.4

0.114

100~300mm 0.058 note1

0.066

note1: Calculated value; 0.098 + (0.114-0.098)/(0.1) x (0.333-0.3) = 0.10328 #

S>0.5h or ≤ 0.5h ? ℓ = 30mm h = 10mm S = 7mm Worksheet: This is a subsurface defect for S>0.5h = 10/40 = 0.25 h/ℓ = 10/30 = 0.333, h/t = 0.10328 h/t Conclusion: The discontinuity is “Reject” actual

allowable

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t = 40mm

Aspect Ratio h/ℓ

CASE STUDY #2 ℓ = 30mm h= 10mm S = 7mm t = 300mm

0.3 0.333 0.35 0.4

Sub-Surface h/t 25~64mm 0.098

0.114

100~300mm 0.058 note1 0.06064 0.066

Note1: Calculated value; 0.058 + (0.066-0.058)/(0.1) x (0.333-0.3) = 0.06064 #

S>0.5h or ≤ 0.5h ? ℓ = 30mm h = 10mm S = 7mm Worksheet: This is a subsurface defect for S>0.5h = 10/300 = 0.0333 h/ℓ = 10/30 = 0.333, h/t = 0.06064 h/t Conclusion: The discontinuity is “Accept” actual

allowable

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t = 300mm

CASE STUDY #3 ℓ = 30mm h= 10mm S = 3mm t = 300mm

Surface h/t

Aspect Ratio h/ℓ

25~64mm

100~300mm

0.3

0.064

0.038

0.333 0.35

0.074

0.044

Note1: Calculated value; 0.038 + (0.044-0.038)/(0.05) x (0.333-0.3) = 0.04196 #

S>0.5h or ≤ 0.5h ? ℓ = 30mm h = 10mm S = 3mm Worksheet: This is a surface defect for S<0.5h = 10/300 = 0.0333 h/ℓ = 10/30 = 0.333, h/t = 0.04196 h/t Conclusion: The discontinuity is “Accept” actual

allowable

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t = 300mm

CASE STUDY #4 ℓ = 30mm h= 15mm S = 3mm t = 300mm

Surface h/t

Aspect Ratio h/ℓ

25~64mm

100~300mm

0.5

0.087

0.052

Note1: Calculated value; 0.038 + (0.044-0.038)/(0.05) x (0.333-0.3) = 0.04196 #

S>0.5h or ≤ 0.5h ? ℓ = 30mm h = 15mm S = 3mm Worksheet: This is a surface defect for S<0.5h = 15/300 = 0.05 h/ℓ = 15/30 = 0.5, h/t = 0.04196 h/t Conclusion: The discontinuity is “Accept” actual

allowable

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t = 300mm

CASE STUDY #5 ℓ = 30mm h= 15mm S = 3mm t = 300mm

Surface h/t

Aspect Ratio h/ℓ

25~64mm

100~300mm

0.5

0.087

0.052

S>0.5h or ≤ 0.5h ? ℓ = 30mm h = 20mm S = 3mm Worksheet: This is a surface defect for S<0.5h = 20/300 = 0.0667 h/ℓ = 20/30 = 0.667, h/t = ?? (no value given) h/t Conclusion: The discontinuity is “???” actual

allowable

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t = 300mm

CASE STUDY #6 ℓ = 50mm h= 15mm S = 3mm t = 300mm

Surface h/t

Aspect Ratio h/ℓ

25~64mm

100~300mm

0.3

0.064

0.038

S>0.5h or ≤ 0.5h ? ℓ = 50mm h = 15mm S = 3mm Worksheet: This is a surface defect for S<0.5h = 15/300 = 0.05 h/ℓ = 15/50 = 0.3, h/t = 0.038 h/t Conclusion: The discontinuity is “Reject” actual

allowable

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t = 300mm

Sridhar Samiyaiah/ Charlie Chong

Surface

Aspect Ratio

Sub-Surface

25~64mm

100~300mm

25~64mm

100~300mm

h/l

h1/t

h2/t

h3/t

h4/t

0.031

0.019

0.068

0.04

0.05

0.033

0.02

0.1

0.036

0.022

0.076

0.044

0.15

0.041

0.025

0.2

0.047

0.028

0.086

0.05

0.25

0.055

0.033

0.3

0.064

0.038

0.098

0.058

0.35

0.074

0.044

0.4

0.083

0.05

0.114

0.066

0.45

0.085

0.051

0.5

0.087

0.052

0.132

0.066

0.6

0.156

0.088

0.7

0.18

0.102

0.8

0.21

0.116

0.9

0.246

0.134

0.286

0.152

Sridhar Samiyaiah/ Charlie Chong

Aspect Ratio h/l vs Acceptance Criteria for Surface & Sub-Surface Indications h1/t

h2/t

h3/t

h4/t

1, 0.286

0.9, 0.246

0.8, 0.21 0.7, 0.18 0.6, 0.156

1, 0.152 0.9, 0.134

0.5, 0.132 0.8, 0.116

0.4, 0.114 0.7, 0.102

0.3, 0.098 0.5, 0.087 0.45, 0.085 0.4, 0.083 0.1, 0.076 0.35, 0.074 0, 0.068 0.3, 0.064 0.4, 0.066 0.5, 0.066 0.3, 0.058 0.25, 0.055 0.5, 0.052 0.45, 0.051 0.4, 0.05 0.2, 0.047 0.05 0.2, 0.35, 0.044 0.1, 0.044 0.15, 0.041 0, 0.04 0.3, 0.038 0.1, 0.036 0.05, 0.033 0.25, 0.033 0, 0.031 0.2, 0.028 0.15, 0.025 0.1, 0.022 0.05, 0.02 0, 0.019 0.2, 0.086

Sridhar Samiyaiah/ Charlie Chong

0.2

0.4

0.6

0.6, 0.088

0.8

1.2

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B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING – B31 Approval Date: January 23, 2007 or greater than the actual length of the flaws in the qualification block.

B31 Case 181-1

Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3

TABLE 1 FLAW ACCEPTANCE CRITERIA FOR WELD THICKNESS LESS THAN 25 mm (1 in.)

Inquiry: Under what conditions and limitations may alternative UT acceptance criteria apply in lieu of those described in para. 344.6.2 of ASME B31.3.

Surface flaw Subsurface flaw

Reply: It is the opinion of the Committee that alternative UT acceptance criteria as described in this case may be applied in lieu of those described in para. 344.6.2 of ASME B31.3 provided that all of the following requirements are met: (a) The ultrasonic examination area shall include the volume of the weld, plus the lesser of 25 mm (1in) or t on each side of the weld (b) A documented examination strategy or scan plan shall be provided showing transducer placement, movement, and component coverage that provides a standardized and repeatable methodology for weld acceptance. The scan plan shall also include ultrasonic beam angle used, beam directions with respect to weld centerline, and pipe volume examined for each weld. The documentation shall be made available to the owner’s Inspector. (c) The ultrasonic examination shall be performed in accordance with a written procedure conforming to the requirements of Section V, Article 4.1 The procedure shall have been demonstrated to perform acceptably on a qualification block(s). Qualification block(s) shall be in accordance with Section V, Article 4, T434.1.2 through T-434.1.6. The qualification block(s) shall be prepared by welding or the hot isostatic process (HIP) and shall contain a minimum of three flaws, oriented to simulate flaws parallel to the production weld's fusion line as follows: (1) one surface flaw on the side of the block representing the pipe OD surface (2) one surface flaw on the side of the block representing the pipe ID surface (3) one subsurface flaw (4) If the block can be flipped during UT examination, then one flaw may represent both the ID and OD surfaces. Thus only two flaws may be required. Flaw size shall be no larger than the flaw in Table 1 or 2 for the thickness to be examined. Acceptable performance is defined as response from the maximum allowable flaw and other flaws of interest demonstrated to exceed the reference level. Alternatively, for techniques that do not use amplitude recording levels, acceptable performance is defined as demonstrating that all imaged flaws with recorded lengths, including the maximum allowable flaws, have an indicated length equal to

a/t < 0.087 < 0.143

ℓ < 6.4 mm (0.25 in.) < 6.4 mm (0.25 in.)

GENERAL NOTES: (a) t = the thickness of the weld excluding any allowable reinforcement. For a buttweld joining two members having different thickness at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, the thickness of the throat of the fillet weld shall be included in t. (b) A subsurface indication shall be considered as a surface flaw if the separation (S in Fig. 1) of the indication from the nearest surface of the component is equal to or less than half the through dimension (2d in Fig. 1, sketch [b]) of the subsurface indication.

(d) The ultrasonic examination shall be performed using a device employing automatic computer based data acquisition. The initial straight beam material examination (T-472 of Section V, Article 4) for reflectors that could interfere with the angle beam examination shall be performed (1) manually, (2) as part of a previous manufacturing process, or (3) during the automatic UT examination provided detection of these ref1ecctors is demonstrated as described in Para. (c)

1 Sectorial scans (S-scans) with phased arrays may be used for the examination of welds, provided they are demonstrated satisfactorily in accordance with para. (c). S-scans provide a fan beam from a single emission point, which covers part or all of the weld, depending on transducer size, joint geometry, and section thickness. While S-scans can demonstrate good detectability from side drilled holes, because they are omnidirectional reflectors, the beams can be misoriented for planar reflectors (e.g., lack of fusion and cracks). This is particularly true for thicker sections, and it is recommended that multiple linear passes with S-scans be utilized for components greater than 25 mm (1 in.) thick. An adequate number of flaws should be used in the demonstration block to ensure detectability for the entire weld volume.

Revised: August 29, 2008

B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING â&#x20AC;&#x201C; B31 Approval Date: January 23, 2007 (e) Data is recorded in unprocessed form. A complete data set with no gating, filtering, or thresholding for response from examination volume in para. (a) above shall be included in the data record. (f) Personnel performing and evaluating UT examinations shall be qualified and certified in accordance with their employer's written practice. ASNT SNT-TC-lA or CP-189 shall be used as a guideline. Only Level II or III personnel shall analyze the data or interpret the results. (g) Qualification records of certified personnel shall be approved by the ownerâ&#x20AC;&#x2122;s Inspector per para. 342.1. (h) In addition, personnel who acquire and analyze UT data shall be qualified and certified in accordance with (f) above and shall be trained using the equipment in (d) above, and participate in the demonstration of (c) above. (i) Data analysis and acceptance criteria shall be as follows: (1) Data Analysis Criteria. Reflectors exceeding the limits in either (a) or (b) below, as applicable, shall be investigated to determine whether the indication originates from a flaw or is a geometric indication in accordance with para. ( i ) ( 2 ) below. When a reflector is determined to be a flaw, it shall be evaluated for acceptance in accordance with para. (i)(4), Flaw Evaluation and Acceptance Criteria. (a) For amplitude-based techniques, the location, amplitude, and extent of all reflectors that produce a response greater than 20% of the reference level shall be investigated. (b) For nonamplitude-based techniques, the location and extent of all images that have an indicated length greater than the limits in (1) or (2) below, as applicable, shall be investigated. (1) For welds in material equal to or less than 38 mm (1 1/2 in.) thick at the weld, images with indicated lengths greater than 3.8 mm (0.150 in.) shall be investigated.

(2) For welds in material greater than 38 mm (1 1/2 in). thick but less than 64 mm (2 1/2 in.) thick at the weld, images with indicated lengths greater than 5 mm (0.200 in.) shall be investigated. (2) Geometric. Ultrasonic indications of geometric and metallurgical origin shall be classified as follows: (a) Indications that are determined to originate from the surface configurations (such as weld reinforcement or root geometry) or variations in metallurgical structure of materials (such as cladding to base metal interface) may be classified as geometric indications, and (1) need not be characterized or sized in accordance with ( i )(3) below; (2) need not be compared to allowable flaw acceptance criteria of Table 1 or 2; (3) the maximum indication amplitude and location shall be recorded, for example: internal attachments, 200% DAC maximum amplitude, 25 mm (1in.) above the weld centerline, on the inside surface, from 90 to 95 deg. (b) The following steps shall be taken to classify an indication as geometric: (1) Interpret the area containing the reflector in accordance with the applicable examination procedure; (2) Plot and verify the reflector coordinates, provide a cross-sectional display showing the reflector position and surface discontinuity such as root or counterbore; and (3) Review fabrication or weld prep drawings. (c) Alternatively, other NDE methods may be applied to classify an indication as geometric (e.g., alternative UT beam angles, radiography,). The method employed is for information only to classify the indication as geometric and ASME B31.3 requirements for examination techniques are only required to the extent that they are applicable.

B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING – B31

TABLE 2 FLAW ACCEPTANCE CRITERIA FOR 25 mm (1 in) TO 300 mm (12 in.) THICK WELD 25 mm (1 in.) ≤ t ≤ 64 mm (21/2 in.),

100 mm (4 in.) ≤ t ≤ 300 mm (12 in.)

Aspect

Surface

Subsurface

Surface

Subsurface

Ratio,

Flaw,

a/ℓ

a/t

0.00

0.031

0.034

0.019

0.020

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

0.033 0.036 0.041 0.047 0.055 0.064 0.074 0.083 0.085 0.087

0.038 0.043 0.049 0.057 0.066 0.078 0.090 0.105 0.123 0.143

0.020 0.022 0.025 0.028 0.033 0.038 0.044 0.050 0.051 0.052

0.022 0.025 0.029 0.033 0.038 0.044 0.051 0.058 0.067 0.076

GENERAL NOTES: (a) t = thickness of the weld excluding any allowable reinforcement. For a buttweld joining two members having different thickness at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, the thickness of the throa t t of the fillet weld shall be included in t. (b) A subsurface indication shall be considered as a surface flaw if separation (S in Fig. 1) of the indication from the nearest surface of the component is equal to or less than half the through thickness dimension (2d in Fig. 1, sketch [b]) of the subsurface indication. (c) If the acceptance Criteria in this table results in a flaw length, ℓ , less than 6.4 mm (0.25 in.) , a value of 6.4 mm (0.25 in.) may be used. (d) for intermediate flaw aspect ratio a/ℓ and thickness t (64 mm [2 1/2 in] < t < 100 mm [4 in.]) linear interpolation is permissible.

B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING â&#x20AC;&#x201C; B31

(3) Flaw Sizing. Flaws shall be sized in accordance with a procedure demonstrated to size similar flaws at similar material depths. Alternatively, a flaw may be sized by a supplemental manual technique so long as it has been qualified by the demonstration above. The dimensions of the flaw shall be determined by the rectangle that fully contains the area of the flaw. (Refer to Figs. 1-5.) (a) The length (â&#x201E;&#x201C;) of the flaw shall be drawn parallel to the inside pressure-retaining surface of the component. (b) The depth of the flaw shall be drawn normal to the inside pressure retaining surface and shall be denoted as "a" for a surface flaw or "2a" for a subsurface flaw. (4) Flaw Evaluation and Acceptance Criteria. Flaws shall be evaluated for acceptance using the applicable criteria of Table 1 or 2 and with the following additional requirements:

(a) Surface Connected Flaws. Flaws identified as surface flaws during the UT examination may or may not be surface connected. Therefore, unless the UT data analysis confirms that that flaw is not surface connected, it shall be considered surface connected or a flaw open to the surface, and is unacceptable unless a surface examination is performed in accordance with (1) or (2) below. If the flaw is surface connected, the requirements above still apply; however, in no case shall the flaw exceed the acceptance criteria in ASME B31.3 for the method employed. Acceptable surface examination techniques are: (1) Magnetic particle examination (MT) in accordance with para 344.3 and Table 341.3.2 of ASME B31.3, or (2) Liquid penetrant examination (PT) in accordance with para 344.4 and Table 341.3.2 of ASME B31.3.

B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING â&#x20AC;&#x201C; B31

B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING – B31

(i) above shall be reviewed by a UT level III individual. When flaw evaluation or characterization of (i) above are performed by another qualified level II or III individual, their review may be performed by another individual from the same organization. Examination data review shall include verification that the records indicated in Section V, Article 4, T-491 and T492 and records noted in the applicable Article 4 appendices are available. B31.3, para 346 applies. Alternatively, the review may be achieved by arranging for a data acquisition and initial interpretation by a Level II individual qualified in accordance with paras. (f) and (h) above, and a final interpretation and evaluation shall be performed by a Level III individual qualified similarly. The Level III individual shall have been qualified in accordance with para. (f) above, including a practical examination on flawed specimens. (d) With the owner’s approval, the flaw acceptance criteria in Table 2 for wall thicknesses between 25 mm (1 in.) and 54 mm (2½ in.) may be used for wall thicknesses of less than 25 mm (1 in.). The maximum allowable flaw depth for qualification purposes shall be specified.

(b) Multiple Flaws (1) Discontinuous flaws shall be considered a singular planar flaw if the distance between adjacent flaws is equal to or less than S as shown in Fig. 2. (2) Discontinuous flaws that are oriented primarily in parallel planes shall be considered a singular planar flaw if the distance between the adjacent planes is equal to or less than 1/2 in. (13 mm). (Refer to Fig. 3.) (3) Discontinuous flaws that are coplanar and nonaligned in the through-wall thickness direction of the component shall be considered a singular planar flaw if the distance between adjacent flaws is equal to or less than S as shown in Fig. 4. (4) Discontinuous flaws that are coplanar in the through-wall direction within two parallel planes 13 mm (1/2 in.) apart (i.e., normal to the pressure-retaining surface of the component) are unacceptable if the additive flaw depth dimension of the flaws exceeds those shown in Fig. 5. (c) Subsurface Flaws. Flaw length (ℓ) shall not exceed 4t. (j) Examination data including the data record of (c) above and data analysis or interpretation of

B31 CASE 181-1 CASES OF THE CODE FOR PRESSURE PIPING â&#x20AC;&#x201C; B31

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3 d) Personnel demonstration requirements Original Inquiry: Under what conditions and shall be as stated in ASME Section V, limitations may alternative UT acceptance Article 4 Mandatory Appendix VII. criteria apply in lieu of those described in para. 4) Examination 344.6.2 of ASME B31.3? a) The initial straight beam scan for reflectors that could interfere with the When specified by the owner, the ultrasonic angle beam examination shall be examination acceptance criteria included below performed (a) manually, (b) as part of a may be applied for welds in material greater previous manufacturing process, or (c) than or equal to 25mm (1.0 in.) in thickness1 in during the weld examination, provided accordance with ASME B31.3 provided the detection of these reflectors is included following requirements are met: in the demonstration as required in 1(c) above. 1) General/Scope: b) The examination area shall include the a) The examination shall be conducted volume of the weld, plus the lesser of using automated or semi-automated 25mm (1.0 in.) or t of adjacent base techniques utilizing computer based data metal. Alternatively, the examination acquisition. volume may be reduced to include the b) The examination shall be performed in actual heat affected zone (HAZ) plus accordance with a written procedure 6mm (0.25 in.) of base material beyond approved by a Level III and conforming the heat affected zone on each side of to the requirements of ASME Section V, the weld, provided the extent of the Article 4 Mandatory Appendix VIII and: weld HAZ is measured and documented. i) For Phased Array – ASME Section c) Scanning may be peformed at reference V, Article 4, Mandatory Appendix level provided the procedure V qualification was performed at reference ii) For Time of Flight Diffraction level. (TOFD) - ASME Section V, Article 5) Data Recording 4, Mandatory Appendix III Data shall be recorded in the c) Procedure qualification shall meet the unprocessed form with no thresholding. requirements of ASME Section V, The data record shall include the Article 4, Mandatory Appendix IX. complete examination area as specified 2) Equipment in (4)(b) above. A mechanical guided scanner capable of maintaining a fixed and consistent search unit position relative to the weld centerline shall be used. 3) Personnel a) Set-up and scanning of welds shall be 1 For wall thicknesses less than 25mm (1.0 in.), the performed by personnel certified as acceptance criteria stated in paragraph 344.6.2 of B31.3 Level II or III (or by Level I personnel shall be used. under the direct supervision of Level II personnel). b) Interpretation and evaluation of data shall be performed by Level II or III personnel. c) Examination personnel shall be qualified and certified following a procedure or program as described in ASME BPV Code, Section V, Article 1, T-120 (e), (f), (h) and (i).

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3 dimension (h in Figure 1, sketch [b]) 6) Data Analysis of the subsurface indication. a) Reflectors exceeding the limits below b) Multiple Flaws shall be investigated to determine i) Discontinuous flaws that are whether the indication originates from a oriented primarily in parallel planes flaw or is a geometric indication in shall be considered to lie in a single accordance with 6(b) below. plane if the distance between the i) For amplitude based techniques, the adjacent planes is equal to or less location, amplitude, and extent of all than 13mm (0.50 in.) or 0.5t, reflectors that produce a response whichever is less. greater than 20% of the reference ii) If the space between two flaws level shall be investigated. aligned along the axis of weld is less ii) For non-amplitude based than the height of the flaw of greater techniques, the location and extent height, the two flaws shall be of all images that have an indicated considered a single flaw. length greater than 4.0mm (0.16 in.) iii) If the space between two flaws shall be investigated. aligned in the through-thickness b) Ultrasonic indications of geometric dimension is less than the height of and/or metallurgical origin shall be the flaw of greater height, the two classified as specified in ASME Section flaws shall be considered a single V, Article 4 Paragraph T-481. flaw. c) Alternatively, other techniques or NDE 8) Flaw Acceptance Criteria methods may be used to classify an indication as geometric (e.g., alternative Flaws shall be evaluated against the beam angles, radiography). The method applicable acceptance criteria of Table 1 employed is for information only to or 2, except that flaw length (l) shall not classify the indication as geometric, and exceed 4t, regardless of flaw height (h) ASME B31.3 requirements for or the calculated aspect ratio. examination techniques are only required to the extent they are applicable. 7) Flaw Evaluation a) The dimension of the flaw(s) shall be determined by the rectangle that fully contains the area of the flaw(s). (Refer to Fig. 1) i) The length, ℓ, of the flaw shall be drawn parallel to the inside pressure retaining surface of the component. ii) The height, h, of the flaw shall be drawn normal to the inside pressure retaining surface of the component. iii) The flaw shall be characterized as a surface or subsurface flaw, as shown in Figure 1. iv) A subsurface indication shall be considered as a surface flaw if the separation (S in Figure 1) of the indication from the nearest surface of the component is equal to or less than half the through wall

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3 TABLE 1 Acceptance Criteria for Surface Flaws Weld Thickness Aspect Ratio, h/ℓ

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

25mm to 64mm (1.0 in. to 2.5 in.) h/t < 0.031 < 0.033 < 0.036 < 0.041 < 0.047 < 0.055 < 0.064 < 0.074 < 0.083 < 0.085 < 0.087

100mm to 300mm (3.9 in. to 11.8 in.) h/t < 0.019 < 0.020 < 0.022 < 0.025 < 0.028 < 0.033 < 0.038 < 0.044 < 0.050 < 0.051 < 0.052

TABLE 2 Acceptance Criteria for Subsurface Flaws Weld Thickness Aspect Ratio, h/ℓ

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

25mm to 64mm (1.0 in. to 2.5 in.) h/t < 0.068 < 0.076 < 0.086 < 0.098 < 0.114 < 0.132 < 0.156 < 0.180 < 0.210 < 0.246 < 0.286

100mm to 300mm (3.9 in. to 11.8 in.) h/t < 0.040 < 0.044 < 0.050 < 0.058 < 0.066 < 0.076 < 0.088 < 0.102 < 0.116 < 0.134 < 0.152

B31 Case 181‐2 (Approval Date: January 4, 2012) Use of Alternative Ultrasonic Examination Acceptance Criteria in ASME B31.3 includes a fillet weld, the effective throat dimension of the fillet weld shall be included in t. (b) Aspect Ratio (h/ℓ) used may be determined by rounding the calculated h/ℓ down to the nearest 0.05 increment value within the column, or by linear interpolation. (c) For intermediate thickness t (weld thicknesses between 64mm and 100mm [2.5 in. and 3.9 in.]) linear interpolation is required to obtain h/t values.

S < 0.5h (a) Surface Flaw

(b) Surface Flaw

S > 0.5h (c) Subsurface Flaw

Figure 1: Surface and Subsurface Indications

Phased Array Pipework Inspection

Oceaneering offers fully code compliant Phased Array Ultrasonic Testing (PAUT) as a replacement to on-site radiography. Developments in construction codes have allowed PAUT to be used as a direct replacement to Radiography on piping butt welds to meet the quality control requirements of ASME B31.3 and B31.1 and numerous European standards. PAUT can be worked towards both workmanship and Engineer Critical Assessment (ECA) acceptance criteria, with data being suitable for accurate sizing and defect characterization.

Detectable Defects • Cracks • Lack of Fusion • Lack of Penetration • Slag Inclusions • Porosity

PAUT enables reduced inspection time by simultaneously collecting multiple angle ultrasonic data in a one pass scan from either side of the weld. Typical inspection rates are between 15-20 butts per shift. By ensuring accurate scan plans and specifically designed techniques all construction defects are readily detected, sized and sentenced accordingly.

10/12

www.oceaneering.com

Phased Array Pipework Inspection Data Analysis

Advantages

Sophisticated analysis software allows experienced operators to interrogate welds from multiple orientations including a comprehensive evaluation of the weld root, fusion face and weld toes.

• Radiation free ultrasonic technique • Welds from 3/4 inch in diameter up to flat plate may be inspected. • Wall thicknesses from 4mm. (N.B. Wall thickness below 8mm may require a trial / validation period.) • Independent from site utilities due to battery operation and irrigation system • Rapid inspections with digital recording of data • Digitally encoded scanning for accurate sizing • Highly sensitive to fusion face flaws • Free viewing software available to allow the client to review inspection data • ASME and European code compliant

Piping Construction Codes • ASME B31.3 code case 181.2, which permits the use of PAUT on wall thicknesses >25mm to a fracture mechanics sentencing criteria. The sentencing for this code case is based on a fracture mechanics module and requires qualification. • B31.1 and code case 179, which together permits the use of PAUT on all thicknesses. The sentencing for this code is based on workmanship criteria and does not specifically require qualification. • BS EN ISO 17640: 2010 - Techniques, testing levels and assessment for non-destructive and ultrasonic testing of welds • BS4515: 1-2004 Specification for welding of steel pipelines on land and offshore. Carbon and carbon manganese steel pipelines. PAUT allowable with client dispensation. • BE EN ISO 13588 - Non-Destructive Testing of Welds - Ultrasonic Testing - use of Semiautomated PA

Limitations • Surface preparation is required to allow the collection of quality data • 100mm of radial and axial clearance is required for scanner fitment (NB small bore scanner available for restricted access scanning.)

Phased array small bore scanner

Oceaneering International, Inc. | Asset Integrity | 11911 FM 529 | Houston, TX 77041 email: Asset-Integrity@oceaneering.com | oceaneering.com/asset-integrity OCEANEERING® is a registered trademark of Oceaneering International, Inc.

•Click to edit Master text styles –Second level

Click to edit Master title style Phased Array and Time of •Third level –Fourth level Flight »Fifth Diffraction (TOFD) level Codes and Specifications Michael Moles NAVSEA 271st meeting, May 2011 1

Outline on AUT Codes  ASME

– AUT and Phased Array codes

 ASME

- Code requirements

 TOFD

Codes – incl. ASME

 Other

code activities – API, ASTM, AWS, EN, ISO etc.

 Summary

ASME Codes

ASME AUT Codes Today  AUT

dominated for years by ASME Code Case 2235 (from Sections I, VIII and XII)

 Now

replaced by three Mandatory Appendices (publ. July 2010) in Section V

 No

commitment to specific technologies: wide variety of options - technique, equipment, mechanics, data displays etc. 4

ASME Mandatory Appendices VI-VIII  Based

on Performance Demonstration (Procedure Qualification)

 Requires

detection of three defects (ID, OD, sub-surface)

 Requires

full data collection and encoder

 (Modified

versions of CC 2235 in API 620 App U, B31.3 CC 181 etc.) 5

ASME Mandatory Appendices VI-VIII  MUCH

easier to read and use than CC 2235  Written in plain English  For example, Performance Qualification allows + 25% on wall thickness and 0.9-1.5 on diameter.

The Portable Approach One person operation: • OmniScan • twin phased arrays, • TOFD • handscanner • couplant and pump • linear scanning. 7

Phased Array Codes and Code Cases  Three

AUT Mandatory Appendices (VI-VIII):

– Workmanship – Fracture Mechanics-based – Procedure Qualification (Performance Demo)  Two

PA Mandatory Appendices (IV-V):

– Manual PA (E-scans and S-scans) – Encoded linear scanning using linear arrays (Eand S-scans) 8

ASME Phased Array Mandatory Appendix Requirements

Phased Array Mand. App. Requirements  Calibrate

all beams (OK for OmniScan)  Use same Focal Law for cal as for scanning For encoded scanning:  Develop Scan Plan to show coverage and appropriate angles  Use two (or more) S-scans if required  Scan parallel to weld with encoder/full data collection at fixed distance from centerline 10

Phased Array Mand. App. Requirements  Requires

“appropriate angles” for bevel incidence angles (undefined)

 Usual

‘Essential Variable’ recording requirements

 Requires

50% beam overlap  Requires <5% data drop-out for encoded scanning  Extensive reporting requirements. 11

Calibrating wedge delay The operator sets a time gate with enough width to encompass all the reflections at all angles and positions. Operator then â&#x20AC;&#x153;calibratesâ&#x20AC;? the wedge delay using the automatic calibration process.

Sensitivity calibration  Need

to correct for angle effects (ACG) and time effects (TCG)  OmniScan has ACG correction, but easiest to use Auto-TCG function.  Auto-TCG does both ACG and TCG operations in a single step. 13

Sample Auto-TCG results

Scan Plans

Ray tracing using ESBeamTool with sample Bevel Incidence Angles (arrowed) calculated on 25 mm wall double-V weld. Can check if angles â&#x20AC;&#x153;not appropriateâ&#x20AC;? 15

ASME B31.3 Code Case 181 (-2)  Recently

re-written - again  Currently out for ballot  Essentially converts CC 181-2 to “workmanship”  Overall, should be a major step forward for pipes  In addition, ASME Section V Code Case 2638 allows much greater flexibility in cal blocks. 16

TOFD Codes, especially ASME

TOFD Signals Receiver

Transmitter

Lateral wave

Back-wall reflection BW

Upper tip

Lower tip 18

Typical TOFD Display •Gray scale and rf for phase info. •OD and ID visible •Defects detectable in middle

•L-wave display only (usually)

TOFD Advantages and Disadvantages  Excellent

PoD for mid-wall defects  Good detection of mis-oriented defects  Rapid (and relatively low cost) inspections  Dead

zone of ~3mm at outer surface  Potential dead zone at inner surface  Can be difficult to interpret. 20

TOFD Codes  Well

“codified”, primarily from Europe

 “Invented”

and developed there

 Some

pluses and minuses of various TOFD codes, e.g. how to calibrate etc

 Well-used

and well-developed technique

 BUT,

does require skilled and trained operators. 21

TOFD Codes  BS7706

essentially a “guideline”  EN583_6 good, but not well known in North America  Replaced by EN14751  ASTM E-2373-04 published  ASME TOFD Code (Section V Article 4 Mandatory Appendix III) published in 2006  ASME TOFD Interpretation Manual (Nonmandatory App. N) published. 22

ASME TOFD Code  Good

code; requires calibrating on ASME side-drilled holes  Current calibration alternatives from Europe: – known defects – grain noise – lateral wave  ASME

requires conventional UT for ID and OD to cover off dead zones (unlike most other TOFD Codes). 23

ASME TOFD Code Calibration

T/4 3T/4

Weld Thickness in. (mm)

Hole Diameter in. (mm)

Up to 1 (25)

3/32 (2.4)

Over 1 (25) thru 2 (50)

1/8

Over 2 (50) thru 4 (100) Over 4 (100)

(3.2) 3/16 (4.8) 1/4 (6)

Calibration using standard ASME notches Defined in Mandatory Appendix III. 24

Other Code Activities â&#x20AC;&#x201C; API, AWS, ASTM, EN/ISO etc.

Code activities - API  API

similar in approach to ASME; two organizations typically work together

 Approval

using PA for API UT 1 and UT 2 procedures with no changes

 Essentially

scan known samples using new technology/techniques

 Phased

arrays now widely used for API, e.g. API RP2X and API 1104. 26

Code activities - AWS A

“prescriptive” code, different from ASME

 With

2006 version => new technology and technique approvals are codified

 Major

problem: each case requires the “Engineers” approval

 Working  AWS

on mandatory Annex for AUT

responding - slowly. 27

Code activities – ASTM (1)  ASTM

E-2491-06 Recommended Practice for phased array set-up

 Requires

full “angle corrected gain” (ACG) and “time corrected gain (TCG) over SDH calibration range

 Limits

to angular range based on recommendations and calibration. 28

Code activities – ASTM (2)  Recent

E-2700 RP for PA of welds  Essentially allows contact testing for ferritic steel welds  No great surprises here.

EN/ISO  Still

working on PA code development

 Third

version more realistic, but still needs a little work

 Very

bureaucratic organization

 But

expect EN/ISO phased array code in a couple of years. 30

Code Summary

Code activities – ASME summary  Phased

arrays, TOFD and AUT inherently accepted by ASME (and other codes)

 May

need to get techniques and procedures approved e.g. by Performance Demonstration approaches

 Complete

ASME Phased Array and TOFD (Time-Of-Flight Diffraction) Codes now available. 32

Code activities – other summary  ASTM

RP for PA set-up published (E-2491)

 ASTM

RP for PA of welds published (E-

2700)  API

generally accepts PA

 AWS

D1.1 still requires Engineer’s approval

 Europeans

“still behind” on PA and AUT

codes. 33

Thank you

Any more questions?

Performance Test Protocol for Phased Array UT in Lieu of RT Personnel Qualification Revision 2.1, 1/21/14 1. General The Test Protocol that is to be used by ultrasonic testing (UT) examiners to take the Phased Array UT in Lieu of RT Personnel Qualification Test is described in this document. The Examinee shall be familiarized with this protocol before arriving at the Westhollow Technology Center. Prior to the start of each test session, the Test Administrator will conduct an orientation with all Examinees that will cover any changes made to this document. Personnel taking the test shall follow his/her employer’s written Phased Array UT procedure. The Examinee shall provide a copy of the Phased Array UT procedure that will be used during the examination to the Test Administrator prior to taking the test. 2. Testing Details The test session is scheduled to be completed in one workday. The testing will start at 8:00 am, with a lunch break at 12:00 - 12:30 - In Room (must bring own lunch). The examination ends at 5:00 pm. Only one Examinee may leave the testing area at a time. The testing will be monitored at all times to prevent compromise of the test samples. Each examinee will be given a unique test set consisting of 6 qualification test specimens. In general there is no time limit per sample, however some samples may be part of more than one examinee’s test set and sharing the samples will be required. If necessary, time limit provisions may be established. Each examinee must inspect all six samples without any assistance. Each Examinee shall work independently and is not allowed to discuss sample or examination information during or after the testing. All paperwork must be completed and turned in to the Test Administrator at the end of the day. Examinees that fail to complete the testing in the allotted time will be considered to be unsuccessful. No form of data, electronic or otherwise shall be retained by the Examinee after the test is complete. 3. Personnel Requirements Personnel performing the qualification test should be, as a minimum, certified to UT Level II or III in accordance with their employer’s written practice.

4. Equipment Requirements The Examinee is responsible for supplying ALL of the equipment needed for the examination. Sharing of equipment will not be allowed during the demonstration. Listed below are recommended equipment and supplies that should be considered for use during the examination: -

Ultrasonic Phased Array Instrument Ultrasonic Phased Array Transducers. Search unit frequencies should be between 2.25 and 5.0 MHz. Basic Calibration Blocks Calibration Reference Standards (IIW, DSC, Rompas) Indication Plotting Device Pens/Pencils Calculator Couplant Rags

The test administrator will provide extra couplant and rags if necessary. 5. Test Sample Description The test will consist of six carbon steel samples, 2 plates and 4 pipes. The samples details are as follows: -1/2 inch plate, 15 inches weld length, Single Vee, 37.5 degree bevel (1) - 1 inch plate, 15 inches weld length, Single Vee, 37.5 degree bevel (1) - 1.5 inch plate, 14 inches wide, 18” long, 15” weld length, double-Vee butt weld with 30º bevel angle (1) - 12" pipe half section, Wall thickness range from .710" - .767”, 20" weld length, Single Vee, 37.5 degree bevel (1) - 8" pipe, Wall thickness range from .343” - .500", 25" weld length, Single Vee, 37.5 degree bevel (2) Each test specimen will be given a unique identification number. The flaw location and actual specimen identification will be concealed to maintain a “blind test”. Any tape or other type of masking shall not be removed from any of the test samples during or after the examination. 6. Description of Potential Flaws The type of potential flaws includes all flaws listed in the API QUTE plus transverse cracks, both surface connected and non-surface connected. These flaws include: − Inside surface connected crack (ID Crack) − Outside surface connected crack (OD Crack)

− − − − − −

Embedded center line cracking (CL Crack) Lack of root penetration (LOP) Lack of side wall fusion (LOF) Porosity Slag and Inclusions Transverse Cracks

Specific Test Specimens are not required to contain all of the flaws identified above. The number of flaws in each test specimen may vary for each test set. Test specimens may be unflawed along the entire length. All Test Specimens are in the as-welded condition and may contain ID or OD mismatch or other typical non-symmetrical welding geometry. Test Specimens will not contain counterbore geometry. 7. Grading Criteria The Candidate performance will be evaluated in the following categories: a) Detection – Each weld is divided into grading units and each grading unit will be considered as either flawed or unflawed. There will be only defect type in each grading unit. Sufficient data must be provided in order for the Test Administer to determine if the Examinee actually detected the flaw. b) Flaw Characterization – Once a flaw is detected, the Examinee must characterize the flaw to determine the type of flaw, as described in the list in Section 6. The location of the flaw must be accurate with regard to surface connected or volumetric. The flaw must be properly categorized as either being surface connected or subsurface. c) Flaw Length Sizing – The flaw length shall be sized in accordance with the Examinee’s written UT procedure. Over sizing of the flaw length may result in false calls in the adjoining grading unit. d) Flaw Height Sizing – The flaw height shall be sized in accordance with the Examinee’s written UT procedure. e) Flaw Positioning – The flaws that are reported must also be positioned correctly with respect to the weld centerline, upstream (US) or downstream (DS). The grading will include the flaws approximate relationship to the weld centerline. Cross sectional plotting of the indications on the indication data sheet is required to determine the location of the flaw. f) False Calls – A false call is defined as reporting a flaw in a non-flawed grading unit. The Examinee will not know the location of any unflawed grading units.

Each weld is divided into grading units, which are not necessarily of equal length. A single grading unit included both sides of the weld. Grading units are considered unflawed or flawed. Flawed grading units will contain only one flaw. A successful Examinee must meet the minimum requirements in all categories. The test results of pass/fail will be reported to the Examinee within four weeks after the test is complete.

8. Calibration Calibration should be performed and recorded prior to the start of any examination or series of examinations. Calibration should include the complete ultrasonic examination system. The search unit manufacturer and type, exit point, beam angle measurements and other Instrument Settings shall be listed on the provided “Ultrasonic Calibration Data Sheet”. The Primary Reference Sensitivity level and associated distance amplitude correction (DAC) should be established using the inside and outside surface notches in the flowing manner: All Calibration Information shall be listed on the provided “Ultrasonic Calibration Data Sheet”. 9. Examination The examination volume shall consist of the entire weld volume and base material for a distance of ¼ inch from each weld toe for all weld configurations. The search unit angles selected for each component should be chosen based upon the configuration of the component and expected flaw mechanism. Variables such as weld design, weld crown width and material thickness should be evaluated prior to selecting the inspection angles(s). The examination sensitivity (scan gain) should be a minimum of twice (+ 6 dB) the primary reference level. The scanning speed should not exceed 3” per second. Scan Direction: − For the examination of reflectors oriented parallel with the weld, the sound beam should be directed essentially perpendicular to the weld axis from both sides of the weld. − For the examination of transverse indications, the sound beam should be directed essentially parallel to the weld axis.

Scan Pattern: − The probe movement should consist of a raster type scanning sequence providing adequate beam overlap in the indexing direction. This scanning pattern may be supplemented as needed with localized lateral scanning and probe oscillation to provide information important to indication characterization. 10. Indication Evaluation All suspected flaw indications shall be plotted on a cross sectional drawing of the weld in order to accurately identify the specific origin of the reflector. All actual flaw indications, i.e. slag, LOP, LOF cracks, etc. exceeding 20% of the primary reference level shall be reported. 11. Recording and Reporting of Exam Results The component reference information (datum 0 position, direction of flow) that is marked on each sample shall be used for indication reporting. All indications shall be reported on the provided “Indication Report Sheets”. Report of non-relevant indications is not required. Flaw indications 20% of DAC or greater shall be recorded. The following information shall be recorded on the applicable “Indication Report Sheets” for each reported flaw: − Indication # − Flaw Type − % of DAC − Flaw Start and Stop − Flaw Length − Flaw Location (Upstream/CL/Downstream/Transverse) in relationship to the weld centerline − Flaw Location in relationship to the weld volume (ID surface connected, OD surface connected, Embedded) 12. Required Paperwork All paperwork shall be completed and given to the Test Administrator after the test is completed to maintain Test Sample security. No other paper or materials will be allowed at the testing station. The following forms will be required at the completion of the test: Equipment Inventory List A complete list of all equipment used for the examination shall be inventoried and documented on the provided form. This form must be completed before the start of the qualification test.

Ultrasonic Calibration Data Sheet An Ultrasonic Calibration Sheet shall be completed for each test specimen examined. All information must be completed prior to scanning the test samples and should contain the necessary information to assure compliance to the procedure being used. Indication Report Sheet An Indication Data Sheet must be completed for each sample. The Examinee is responsible to properly document the flaw location, length, depth sizing, positioning, characterization, surface connected or subsurface, etc. Each indication must be numbered and all data should be clearly recorded and legible. All flaws should be placed on the Sketch area provided on the form. Test Administrator Check List The Test Administrator shall review the Phased Array examination process for each test candidate. The following shall be reviewed: 1. Phased Array System 2. Scan technique 3. Focus method and depth 4. Data Acquisition 5. Data Analysis 13. Test Security The Test Administrator will monitor this Personnel Qualification Test. Continuous test area surveillance will be maintained to ensure test security. Entry into and out of the testing area will be restricted. The test Administrator will be present during the lunch break to allow Examinees additional time for testing if they choose not to take a lunch break. Purses, backpacks or briefcases will not be allowed at the Examinees testing stations. No cell phones or pagers will be allowed in the testing area. A secure area will be provided for personal items during the testing session. At the conclusion of the Qualification Test, the Phased Array unit digital on-board memory shall be demonstrated to be cleared of all data and images. The Flash card, Memory Card or other Storage Card/Device will be turned in to the Test Administrator at the end of the examination. The Test Administrator will verify that no data is stored on this device, any internal hard drive or computer used for data acquisition. 14. Retest An Examinee failed the performance demonstration test shall not be allowed to re-take the test within 3 months of the previous test.

March 2011

RELIABILITY OF ULTRASONIC INSPECTIONS APPLIED IN LIEU OF RADIOGRAPHY IN ACCORDANCE WITH ASME CODE CASE REQUIREMENTS For: A Group of Sponsors

Summary Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) are increasingly being used in lieu of radiography (RT) due to the introduction of ASME Code Case 2235; “Use of Ultrasonic Examination in Lieu of Radiography” Section I; Section VIII, Divisions 1 and 2; and Section XII. These documents define the conditions and limitations that must be satisfied for UT to be used in place of radiography for welds over 12.5mm thick in pressure vessels and boilers. This same code case has subsequently with some modification been incorporated into the ASME Gas Process Piping Code B31.3, in the form of Code Case 181, which was issued in January 2007. These documents however present only the minimum requirements which are frequently inadequate for the demands of the task in hand and are also often misinterpreted. This project aims to produce a Best Practice Guide for the application of PAUT and TOFD in Lieu of RT and to compare the performance and pass/fail data achieved when applying RT in accordance with ASME requirements and best practice UT (TOFD and PAUT) according to code case requirements. Through this we aim to ensure that ultrasonic inspections conducted in accordance with code case requirements are fit for purpose, to optimise qualification costs, to distinguish between necessary and unnecessary repairs and to clarify the implications of applying PAUT and TOFD in lieu of RT.

WORLD CENTRE FOR MATERIALS JOINING TECHNOLOGY

PR17981

Background Radiography (RT) and ultrasonics (UT) are the two generally-used, NDT methods for the detection of embedded flaws located within the volume of a component. Many codes and standards have traditionally specified RT rather than UT for the detection of such flaws with this being largely based upon the fact that RT unlike manual UT provides a permanent record of the inspections conducted. The two methods have other intrinsic advantages and disadvantages with RT considered inefficient for the detection of planar flaws which must be preferentially aligned to the radiographic beam whilst flaw types such as excess root penetration are difficult to detect with UT. Generally however it is considered that the flaws which RT can detect and sentence but UT cannot are not of structural concern, whereas many large planar defects which UT can detect and sentence but RT cannot are safety critical. The application of computerised data acquisition to UT has allowed the production of hard copies of the results whilst at the same time providing higher reliability, repeatability and improved inspection speed. These improvements when added to the pre-existing advantages of UT over RT such as no radiation hazard, sensitivity to planar flaws and the provision of depth and positioning information mean that there is now considerable interest in the use of UT in lieu of RT. This interest has been increased by the introduction of ASME Code Case 2235; “Use of Ultrasonic Examination in Lieu of Radiography” Section I; Section VIII, Divisions 1 and 2; and Section XII which define the conditions and limitations that must be satisfied for UT to be used in place of radiography for welds over 12.5mm thick in pressure vessels and boilers. This same code case has subsequently with some modification been incorporated into the ASME Gas Process Piping Code B31.3, in the form of Code Case 181, which was issued in January 2007. In both cases, fracture mechanics based acceptance criteria may be used in lieu of good workmanship criteria. These documents, however, present only the minimum requirements which are frequently inadequate for the demands of the task in hand. The documents are also often misinterpreted with examples of these being:  

 

The code cases specify that a qualification block should contain a minimum of 3 flaws. This is often insufficient to represent the weld preparations to be inspected The documents state that the procedure shall have been demonstrated to perform adequately on qualification block(s). Pipe to pipe qualification blocks are often used when the actual weld configurations to be inspected include not just pipe to pipe joints but configurations such as pipe to elbow, pipe to reducer and pipe to tee. The number of qualification blocks employed is often either too few or too many leading to either lower project costs but with high risk or in an excessively onerous qualification process which can have an adverse effect upon project timescales. Inspection procedures and qualification failing to address the requirements of the code case or applicable standards.

Objectives

Benefits



Following completion of the project, sponsors will be equipped to



To compare the performance and pass/fail data when applying RT in accordance with ASME requirements and best practice UT (TOFD and PAUT) according to code case requirements. To produce a Best Practice Guide for the application of PAUT and TOFD in Lieu of RT including: - Qualification strategy. - Applicability of computer simulation. - Test piece design - Number and position of flaws, number of samples.

   

Ensure that ultrasonic inspections conducted in accordance with code case requirements are fit for purpose. Optimise qualification costs. Distinguish between necessary and unnecessary repairs. Clarification of the implications of applying PAUT and TOFD in lieu of RT (e.g. costs, likely repair rates).

Approach A set of welded specimens with known flaws will be fabricated with their dimensions, material, joint preparations and flaws being to be defined by the Sponsors. It is envisaged that these specimens will be of pipe to pipe configuration but the range of specimens could be extended to include more difficult configurations for the ultrasonic techniques to be employed such as pipe to elbow, reducer or tee should a sufficient number of sponsors be obtained. These specimens will be used for both the qualification of the inspection procedures generated and subsequently analysing the capabilities of the techniques and procedures. A number of these specimens will contain only 3 flaws to comply with minimum code case requirements. The following procedures will be produced for the inspection of the test specimens:  



ASME V compliant radiographic procedures. PAUT and TOFD procedures (plus supplementary techniques as appropriate) compliant with ASME V and best practice code case requirements. PAUT and TOFD procedures compliant with ASME V and minimum code case requirements.

These procedures will be approved by the Level 3 qualified NDT Engineers and members of the sponsor group. CIVA modelling of the PAUT and TOFD procedures produced will be conducted to validate their capabilities. CIVA is a semianalytical simulation tool developed for parametric study and development of ultrasonic inspection procedures. As such it is capable of simulating quite complex inspection scenarios. It is composed of a suite of modules which include the computation of the sound field and its interaction with defects. This software is widely accepted by industry and various aspects of its operation have been validated by TWI. Radiographic, PAUT and TOFD inspections of the welded specimens will be conducted using the procedures generated. Following these inspections the data collected will be interpreted by a minimum of three appropriately qualified inspectors.

Comparison of the results of the inspections will be made with measurement after sectioning of actual defects in the specimens. The result from this testing and sectioning will be analysed statistically to compare: 



The capabilities of RT with PAUT and TOFD inspections conducted in accordance with best practice code case requirements The capabilities of PAUT and TOFD inspections conducted in accordance with best practice code case procedures and those conducted in accordance with procedures compliant with the minimum requirements of the code cases.

The results of the inspections conducted and the CIVA modelling will also be analysed to determine the feasibility of a qualification approach based upon the use of qualification pieces representing only the worst case designs supported by CIVA modelling. The results of the project will be presented to the Sponsors in a format that will demonstrate the capabilities of the inspections conducted and the techniques employed.

Deliverables   

TOFD and PAUT procedures approved and validated against code case requirements. A best practice guide for the application of PAUT and TOFD in accordance with code case requirements. A comparison of the performance of code compliant RT and PAUT and TOFD performed in accordance with code case requirements.

Reporting Progress reports providing details of experimental procedures and test data will be issued every six months, prior to Sponsor Group meetings. At the close of the project, a final report detailing the work performed and main results will be presented.

Price and Duration The estimated duration of the programme is 18 months involving test piece manufacture, procedure generation, data collection and data analysis. The price of the full 18 months programme is

estimated at ÂŁ240,000, and it is proposed that six Sponsors each contribute ÂŁ40,000. This price includes the design and the manufacture of the welded specimens. The work will start with a reduced scope as soon as four Sponsors are committed to the project.

A WebEx link will be available for those unable to attend in person For further information please contact:

Launch Meeting

Technical: Ivan Pinson Email: ivan.pinson@twi.co.uk

Date: Wednesday 6 April 2011

Administrative: Danielle Wilson Email:danielle.wilson@twi.co.uk

Time: 13:30 (12:30 Buffet Lunch) Venue: TWI Ltd Granta Park, Great Abington, Cambridge, CB21 6AL

TWI

TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK Tel: +44 (0)1223 899000

Fax: +44 (0)1223 892588

Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

More Info at Open Access Database www.ndt.net/?id=19143

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The advantages of Phased Array Ultrasonic Testing (PAUT) & Time of flight Diffraction (TOFD) Combination instead of using individually on ASME U stamp Pressure vessel fabrication projects.

Hosein Taheri1, Hashem Rahmati2 1. Farin Sout Pishrafteh Engineering Co. Tehran, Iran, info@FSP-NDT.com 2. Pishrafteh NDT Co. Tehran, Iran, info@Pishrafteh.com

Abstract: The Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) technologies have made rapid changes in inspection and reliability in various industries. Ultrasonic phased arrays are a new technology that offers considerable potential for inspecting construction welds. Using electronic control of the beam, phased arrays can scan, sweep, steer and focus the ultrasound. Since welds typically produce defects of known character and orientation, phased arrays can be programmed to optimize weld inspections. These inspections include standard ASME-type pulse echo raster scans, zone discrimination, TOFD and â&#x20AC;&#x153;specialsâ&#x20AC;?, depending on the vessel, weld profile, geometry and specifications. The Time-of-Flight Diffraction technique (TOFD) was originally developed as a method of accurately sizing and monitoring the through wall height of flaws in the industry. It is equally effective in weld inspection for the detection of flaws, irrespective of type or orientation, since TOFD does not rely on the reflectivity of the flaw but uses the diffracted sound initiating from the flaw tips. A major advantage of PAUT & TOFD methods combination is effective procedure for better sizing and location determination of the discontinuities. This paper discusses the combination of PAUT & TOFD methods instead of individually for weld inspection on pressure vessel projects. Keywords: Phased array ultrasonic testing, TOFD, Sectorial scan, Beam intersection, combination of PAUT & TOFD

Introduction: Prevention of disasters is a major concern in any industry. Nondestructive testing as a reliable tool has played an effective and important role in this regard. Conventional Ultrasonic testing of heavy wall thickness pressure vessels is a common practice. Due to the increasing demand for more thorough inspection of pressure vessels, researchers have begun looking into more innovative means of defect measurement. Principally, the Phased Array Ultrasonic Testing (PAUT) & Time-Of-Flight Diffraction (TOFD) flaw detection procedure has been implemented to achieve good results and this combination shown to be an effective procedure for size and location determination of a discontinuities. Specifically, this combination was proven that this is more suitable for thick structures (above 13mm). Today, the PAUT & TOFD procedure is used for operational inspections or quality control of structures during production instead of routine radiography and conventional ultrasonic shear wave procedures. Although TOFD is more often utilized for inspecting welds with simple geometry and fine grain steels, such as welds with thicknesses from 13 mm to 300 mm, it is useful in inspecting more complex geometries. Defects like cracks, lack of penetration, Lack of fusion, porosity, and slag in welds of pressure vessels could be diagnosed via this technique very precisely.

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

The most suitable technique for the complete volume coverage of heavy wall thickness & Nozzle joints and coverage of the weld and heat affected zone would be combined phased array ultrasonic testing (PAUT) and TOFD together which also meet the code (ASME Code Case 2235, ASME Section VIII DIV 1 & DIV 2) requirements [6, 7]. Analysis of the acquired Data is done using Tomoview software and evaluation done in accordance with code case. Finally, a computerized report summarizes the results of the examination. This paper explains the advantages of Phased Array Ultrasonic Testing (PAUT) & Time of flight Diffraction (TOFD) Combination instead of using individually on ASME U stamp Pressure vessel fabrication project carried out at the workshop of one of our client.

Fig. 1: Photos of Pressure vessel welds and Performance of PAUT & TOFD by advanced NDT team at work shop

Inspection Methods: Phased Array Ultrasonic Testing PAUT is an advanced method of ultrasonic testing that has applications in medical imaging and industrial testing. When applied to metals the PAUT image shows a slice view that may reveal defects hidden inside a structure or weld. Phased array uses an array of elements, all individually wired, pulsed and time shifted. A typical user friendly computerized setup calculates the time delays from operator input, or

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

uses a predefined file: test angle, focal distance, scan pattern and so forth. The technique also provides a combination of various scans in the same equipment set-up. B-Scan is a side view, C'Scan is a top view and the S-Scan is a crosssectional view. These views can be better understood in the Figure 2. From a practical viewpoint, ultrasonic phased arrays are merely a technique for generating and receiving ultrasound; once the ultrasound is in the material, it is independent of the generating technique. Consequently, many of the details of ultrasonic testing remain unchanged; for example; if 5 MHz is the optimum testing frequency with conventional ultrasonic, then phased arrays would typically Use the same frequency, aperture size, focal length and incident angle. As such, phased arrays offer significant technical advantages over conventional single-probe ultrasonic; the phased array beams can be steered, scanned, swept and focused electronically.  Electronic scanning permits very rapid coverage of the components, typically an Order of magnitude faster than a single probe mechanical system.

 Beam forming permits the selected beam angles to be optimized ultrasonically by orienting them perpendicular to the predicted defects, for example Lack of Fusion in welds.

 Beam steering (usually called sectorial scanning) can be used for mapping Components at appropriate angles to optimize Probability of Detection. Sectorial Scanning is also useful for inspections where only a minimal scanning length impossible.

 Electronic focusing permits optimizing the beam shape and size at the expected Defect location, as well as optimizing Probability of Detection. Focusing improves Signal-to-noise ratio significantly, which also permits operating at lower pulse voltages.[5] Overall, the use of phased arrays permits optimizing defect detection while minimizing inspection time. Phased arrays offer significant advantages over traditional radiography of welds as well: •

No safety hazards

•

Inspection as soon as weld is cool

•

Better defect detection and sizing

•

Able to penetrate thick sections

•

Compliant with all known codes

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

Fig. 2: Phased array Ultrasonic Testing Images

Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

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Time of Flight Diffraction Time of Flight Diffraction (TOFD) is an advanced automated computerized UT absent technique, used for inservice inspection of welds for heavy walled pressure vessels. TOFD system is capable to scan, store and evaluate flaw indications in terms of height, length and position with greater accuracy and is suitable for weld thickness ranging from 13 mm to 300 mm. The principle and operation of TOFD: The TOFD technique is based on diffraction of ultrasonic waves on tips of discontinuities, instead of geometrical reflection on the interface of the discontinuities. When ultrasound is incident at linear discontinuity such as a crack, diffraction takes place at its extremities in addition to the normal reflected wave. This diffracted energy is emitted over a wide angular range and is assumed to originate at the extremities of the flaw (Fig.3). Scanning is done externally parallel towel axis using longitudinal wave probes with incidence angle range of 45Â° to 70Â°.When flaw is detected during the scanning, Signals from the upper and lower tips of the flaw are displayed as B / D-Scan image. [5]

Fig. 3: Principle of Time of Flight Diffraction (TOFD)

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

In addition to

energies

diffracted by

defects,

TOFD

method will

also detect a

the

surface

(lateral)

wave

travelling

directly

between the

probes

also a back

wall

from

energies that

reach test

and echo

the

back of the

piece

without

interference

from defects.

The TOFD technique uses a pair of probes in a transmitter-receiver arrangement (Fig. 4). Usually longitudinal probes are applied with an angle of incidence range of 45Â° to 70Â°.The diffracted signals are received via the receiver probe and are evaluated with the Ultrasonic System. The difference in the flight of the diffracted wave fronts carry the information on the spatial relationship of the tips of the defect and hence the extent of the defect. TOFD method only evaluates diffracted echoes.

Fig. 4 Transmitter-Receiver arrangement of TOFD

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

Recently we have done Phased array Ultrasonic testing and Time of Flight Diffraction testing in our client site for ASME U stamp pressure vessel. Some of the indications found during the PAUT and TOFD scan are shown below (Fig. 5). Fig. 5: PAUT & TOFD images

PAUT and TOFD disadvantages when they are used individually for weld inspection in heavy wall boiler and pressure vessel 

For amplitude-based techniques (PAUT), the orientation of defects are very important subject, so some of defect like lake of side wall fusion may be miss when we have just access from one side of the weld like circumferential welds in head to shell joint in boiler and pressure vessel, and also in back weld zone in pressure vessel, due to changes in configuration of the welds (X to U), the amplitude-based techniques have not good results for detection and sizing defects in this zone.



For nonamplitude-based techniques (TOFD), the most widely accepted “limitation” is the loss of information due to ring time. This is especially noticeable at the entry surface but a similar zone occurs on the far side (backwall). And also we cannot recognize accurate the location of the defects. As the wall thickness increase, one TOFD transducer pair with proper beam spread and sensitivity is not capable of

Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

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examining the entire weld volume. So, as the wall thickness increases, multiple TOFD transducer pairs will have to be used. Therefore, to examine fully, a heavy wall weld in a single pass, we offer a combined Multichannel (TOFD+PAUT), zonal inspection, testing technique [1] See fig. 6 In short, multiple probes or probe combinations are fixed in a bracket in such an order that together they cover the whole volume of the weld. Each probe or probe combination is directed to a certain portion of the weld and together these probe units cover the whole volume of the weld. Probe characteristics are optimized in a way that all possible weld anomalies are detected with high confidence. This principle is called "zonal discrimination” [2, 3, 4]

In our project the pressure vessel was 84 mm and weld configuration was X mode, so our PAUT and TOFD scan plane was:

1 2 3

Probes 2 PAUT Probes The first pair of TOFD Probes The second pair of TOFD Probes

Frequency(MHz) 2.25 MHz 5 MHz 2.25 MHz

Fig. 6: Scan plan for PAUT and TOFD testing

Equipment Details: We have used Olympus Omni scan MX2 (32128) PAUT & TOFD machine motorized

and

our

scanning

device is HSTM FLEX & Manual Mini wheel Encoder. Fig. 7

Wedge N55°-S 60° L 45°L

Setup Sectorial 40° to 70° ( Full second leg) Beam intersection 2/3t Beam intersection 5/6t

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Fig. 7: PAUT Machine

Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

& TOFD Olympus

PAUT & TOFD Scanner The HSMT-Flexâ&#x201E;˘ is intended for one axis encoded inspection of circumference welds on pipes of 4.5 in. OD (114.3 mm) and greater. The scanner comes equipped with four probe holders but can be mounted with a total of eight probes with optional probe holders. Mounted probes can be either phased array or conventional UT for most efficient inspections. The major characteristic of the scanner is its capacity to bend in the center. This allows the scanner to fit on smaller pipes and also to bring the force of the spring-loaded arm in the radial direction of the pipes for better stability of the wedge, and therefore, optimum data acquisition. For the same reason, optional probe holders that are installed on the outside of the scanner can also pivot. The HSMT-Flex also allows one of its side frames to slide. This feature allows having the probes mounted on the outside of the scanner. This provides a configuration that is well-suited for hard-to-reach places such as pipe-to-component welds. Fig. 8

Fig. 8: PAUT and TOFD Scanner

Results: PAUT & TOFD testing on 84 mm Thick Pressure vessel weld joint results which is approved by Authorized Inspector (AI)

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PAUT and TOFD testing results on a 84 mm pressure vessel Defect (mm) No.

PAUT

TOFD

Combination of PAUT & TOFD

Length of scan (mm)

Type of Defect

START (mm)

END (mm)

Depth (mm)

Height (mm)

Surface Distance (mm)

Remark defect was at back weld zone, so the sizing with PAUT was not accurate ( Fig. 9, 10)

Yes

11600

1820

1955

3.5

Yes

11600

6780

6960

-10

Yes

11600

SL&LOF

5646

5956

-15

Yes

Defect was at TOFD dead Zone ( Fig. 11 )

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

Fig.9: PAUT & TOFD Combination for head to shell weld joint

Fig 10: PAUT Image for shell to shell weld joint

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Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

Fig 11: TOFD Image for Head to shell weld joint

Conclusions:

The Time Of Flight Diffraction (TOFD) & Phased Array Ultrasonic Techniques (PAUT)are rapid, versatile, reliable and an effective advanced UT based NDT method for inspection of welds especially for heavy walled pressure vessels (both pre-service and in-service) with better flaw detection and accurate evaluation of flaw location and flaw sizing. And also combination of PAUT & TOFD proves that a careful preparation of scan plan with appropriate coverage & angles of PAUT & TOFD can detect all flaws that are probable to occur during the welding, thus increasing the reliability of test despite limitation of not having access from both sides of weld to scan apart from this operators, scan plan, procedure, equipment, accessories such as fixtures, scanners, encoders etc. Are needed to be established and validated on a mock up with all probable defects before allowing the same on actual welds.

IRNDT2016

Proceedings of the 3rd Iranian International NDT Conference Feb 21-22, 2016, Olympic Hotel, Tehran, Iran IRNDT2016-T03118

Reference: 1.

ESBeam Tool from Eclipse Scientific, in Canada, http://www.eclipsescientific.com/Software/ESBeamTool/index.html

ASME Boiler & pressure vessel Code, Section V 2010, Article 4, Mandatory Appendix IV, " PHASED ARRAY MANUAL RASTER EXAMINATION TECHNIQUES USING LINEAR ARRAYS"

ASME Boiler & pressure vessel Code, Section V 2010, Article 4, Mandatory Appendix V," PHASED ARRAY E-SCAN AND S-SCAN LINEAR SCANNING EXAMINATION TECHNIQUES"

ASME Boiler & pressure vessel Code, Section V 2010, Article 4, Mandatory Appendix III, " TIME-OF FLIGHT DIFFRACTION (TOFD) TECHNIQUE"

Advances in Phased array Ultrasonic Technology Applications, Olympus NDT (Dr. Michael D.C. Moles), Published 2007

CASES OF ASME BOILER AND PRESSURE VESSEL CODE CASE 2235-9, Use of Ultrasonic Examination in Lieu of Radiography Section I; Section VIII, Divisions 1 and 2; and Section XII

ASME Boiler & pressure vessel Code, Section VIII 2010, Division I and II

Ultrasonic Testing In Lieu of Radiographic Testing

Jack Spanner Program Manager NRC Information Meeting May 2010

Owner Implementation OF UT in Lieu of RT • Owners may submit Relief Request • Available Code cases – B31.1-CC 168 – Sect III- CC N-659-2 – Sect I & VIII- CC 2235-9 – Sect XI – CC N-713 • Incentives – RT restricts personnel access – Use same method for fabrication and ISI examinations – RT can increase length of outage – UT can detect planar flaws reliably © 2010 Electric Power Research Institute, Inc. All rights reserved.

Basic Code Case Requirements N-713, N-659, 2235 and 168 • Automated UT system – Record transducer location – Record raw non-processed data – Image to replace radiograph • Written procedure must be demonstrated – Mockups similar to calibration block/component materials and include weld – 2 or 3 flaws required • Performance based procedure qualification

EPRI Performance Demonstrations Sect III CC N-659 • Owner fabricated 3 ferritic pipe mockups – 14 & 2 each 16 inch diameter – .8 -1.6 inch thick – Numerous fabrication flaws & cracks throughout thickness • EPRI Developed Demonstration protocol – 3rd party administered – Acceptance criteria – Maintained flaw truth security, i.e. Blind tests • 4 vendors participated – Pulse Echo, Time of Flight, & manual techniques – Generally 45 & 60 degree; 2.25 MHz Search units

UT Data and RT Indications

Detection and Identification Results Flaw Detections

0.9

0.8

0.7

Percent

0.6 Correct Flaw Identification 0.5

Correct Evaluation Detection Rate

0.4

0.3

0.2

0.1

0 All Dual Side

Auto Dual Side

Single Side

Manual Dual

UT Capability Summary • All flaws greater than .4 in long detected • All cracks and IP detected • Automated UT slightly better than Manual • Single and dual side scanning had similar results • Porosity most difficult to detect but innocuous – Small porosity rarely detected – RT missed small porosity • UT can be effectively substituted for RT

Canadian Use of UT in lieu of RT for CANDU Feeder Tubes • Enhancements to Code Case N-659-2 and Appendix VIII requirements included: 3 specimen sets consisting of 7 welds created (using all 5 diameters/thicknesses), each set containing 15 flaws • Procedure demonstration (non blind) used all 15 flawed pipe samples (45 specimen flaws) and was required to detect 100% of the flaws (from one side) • All flaws included in the specimen sets were flaws that would be considered relevant construction type flaws: L of F, porosity, cracks, Incomplete Penetration, ID/OD connected and subsurface flaws •

Enhancements to Code Requirements Compared to Appendix VIII • Flaw sizes were based on the acceptance criteria, with acceptable and rejectable flaws in the specimen sets • Grading units were made much smaller… Grading units were made only 0.64” (16mm) larger then the length of the actual flaw 0.79” (20mm) in • Unflawed grading units were only 0.79 length, and grading units had a minimum spacing of only 0.39” (10mm) • Personnel demonstration was a “pure” blind test for detection (and false calls), length sizing, and flaw characterization • Flaw length sizing error was decreased to an RMS of 0.25” (6.4mm) (from 0.75”(19mm))

Observations: Canadian Experience • Used phased array automated system • Avoided 7000 RT shots and 1500 hours of outage time • Owner, regulator, contractor, vendor and ANI cooperated to develop program from N-659-2 and Appendix VIII • UT p personnel worked with welders to improve p workmanship and reduce repair rate • Very beneficial to perform UT in lieu of RT

Latest Draft ASME Section XI Code Case N-713 • Revising N-713 based on two previous studies • Requires recording encoded position and UT data • Section V procedure or Section XI Appendix VIII procedure permitted – Personnel test set requires q at least 10 flaws – Procedure test set requires the equivalent of at least 3 personnel tests – Includes depth sizing and length sizing test sets – Flaw sizes and locations distributed evenly

Latest Draft ASME Section XI Code Case N-713 • Demonstration acceptance criteria – 80% detection rate – 80% correct identification of planar and volumetric flaws – RMSE criteria for depth p and length g tests to be determined • Examination Acceptance criteria based on Sect XI Code – Compare planar and volumetric (cracks, IP, LOF, slag) flaws to Section XI acceptance tables – Use Construction Code criteria if Section XI not applicable

Experience with Code Cases

John R Lilley. C Eng. MInstNDT. ASNT Level 3 RT.UT.PT.MT General Manager, Sonomatic Ltd. Biography John Lilley has been engaged in the NDT industry since 1975, and has held certification to ASNT Level 3 since 1984. He has been instrumental in the application of TOFD and other automated ultrasonic inspection technology to industrial applications since 1988. He has written numerous technical publications and has been a regular contributor to codes and standards over the years. He is currently the General Manager of Sonomatic Ltd, and became a Chartered Engineer in 2007. Background Code Case 2235 was originally issued by the American Society for Mechanical Engineering (ASME) Boiler and Pressure Vessel Code (B&PVC) committee in 1996 [Ref 1]. The enquiry asked “Under what conditions and limitations may an ultrasonic examination be used in lieu of radiography, when radiography is required....”, and the code case text goes on to define these conditions and limitations. It essentially addresses the following: i. ii. iii. iv. v. vi. vii. viii. ix.

Material thickness ranges and volumetric coverage requirements. Requirement for a documented examination strategy. The requirement for the examination to be carried out in accordance with Section V, Article 4 [Ref 2]. The requirement for acceptable demonstration of performance of equipment, procedures and personnel on a qualification block(s). Acceptance criteria based on a combination of flaw height and length measurements which are derived from a linear elastic fracture mechanics procedure. The requirement for automatic computer based data acquisition with data recorded in unprocessed form. Investigation and analysis criteria. Discrimination between surface and sub‐surface flaws. Rules defining interaction in the case of multiple flaws.

Other factors are also addressed, but the above list describes the key elements of the initial code case. There has been extensive discussion through a variety of forums, and the document was revised nine times before being incorporated into the main body of Section VIII in 2008 [Ref 3]. The various revisions have addressed specific refinements although the fundamental document has remained relatively unchanged throughout this process. Along the way, essentially the same code case, with some modification, has been incorporated into the ASME Gas Process Piping Code B31.3 [Ref 4], in the form of Code Case 181, which was issued in January 2007. The generic term ‘Code

Case’ is used throughout this paper to refer to the use of UT in lieu of RT as described in Section VIII of the boiler and pressure vessel code, or in B31.3 Code Case 181. In both cases, fracture‐ mechanics‐based acceptance criteria may be used in lieu of good workmanship criteria. It is important to note that the key difference between conventional and code‐case acceptance criteria is that the former is based on ‘good workmanship’ criteria, and the latter is supported by fracture mechanics calculation. A definition is offered here based on personal experience and interactions with clients, colleagues and partners over a period in excess of thirty year’s involvement with relevant projects, standard committees, R&D forums, seminars, workshops, conferences and legal work. Construction codes and standards are intended to ensure that pressure equipment and structures are designed, fabricated and tested to consistent quality standards in the interests of safety and reliability. The early codes stipulated radiographic testing for the detection of flaws within the weld volume. Radiographic testing is however, inefficient for the detection of planar flaws, which must be a) preferentially aligned to the radiographic beam and b) with a gape that exceeds the applicable radiographic geometric un‐sharpness value. Radiography is efficient however, for the detection of volumetric flaws such as slag entrapment, porosity, undercut, and poor weld profile [Ref 5]. It will also detect certain gross planar flaws, especially where these are associated with other types of volumetric flaw. All of the described volumetric flaws/conditions are indicative of poor workmanship and the codes provide very clear limits on what can be defined as unacceptable in terms of quality standards. Rejection levels are not derived from what is considered to be detrimental to the equipment once placed into service, but what is considered to be poor practice in terms of fabrication quality. This quality culture pervades throughout the entire fabrication process in much the same way as a strong safety culture leads to fewer accidents overall. The inference is that if welding procedures are applied diligently and good workmanship principles are upheld, then it follows that the occurrence of cracking and lack of fusion flaws is likely to be minimised. This process has been observed to be effective in that the incidence of boiler/pressure vessel failures has dramatically decreased following the introduction of codes. Attention to detail in construction NDT spills over to control and care of welding consumables, welding procedures, heat treatment, documentation, etc. It is a fundamental aspect of quality control (QC). There is also a psychological influence in that welders justifiably take pride in their work and are inclined to be averse to the stigma of being classified as ‘poor workmen’ through generating unacceptable levels of repair. Construction ‘good workmanship’ NDT does not need to have a high Probability Of Detection (POD) because individual flaws which may go undetected are not likely to be detrimental to the use of the equipment in service. This is due to the high level of conservatism embodied within the good workmanship approach. The ‘good workmanship’ acceptance criteria of Section VIII Div 2 Part 7 (2008 Addenda) includes, but is not restricted to, the following: • •

Cracks and lack of fusion/penetration – Not permitted Volumetric flaws – Limitations dependent on wall thickness

As an example, in the case of a pressure vessel with a wall thickness of 50mm, a 20mm long slag line would be rejectable to these criteria. The slag line may be less than 2mm in cross‐section and would be expected to be rounded in profile. According to the code cases, a sub‐surface, 39mm long by

4mm high, vertically oriented planar crack in a component of the same wall thickness would be permitted. The difference is that the good workmanship criteria are designed to maintain quality standards, thereby implying fitness‐for‐service, whereas fracture‐mechanics‐based acceptance criteria are designed to eliminate flaws exceeding given dimensions. The performance criteria for the NDT associated with these two approaches are very different. Good workmanship NDT may be less than perfect because it is designed to flag up when the fabrication process is going out of control by picking up systematic flaws (as opposed to detecting all flaws) which are indicative of underlying breakdowns in quality processes. There is less room for manoeuvre with fracture‐ mechanics‐based acceptance criteria, hence the additional requirement for qualification. Adoption of the code cases has steadily increased over the years to the point where in certain circumstances, radiographic testing of pressure vessels under construction has fallen away altogether. This process however, has occurred at a time when the industry has gone through: a) a period of changing regulatory influence (less influence from certifying authorities and insurers), b) increased dependency on formal quality processes and c) increased pressure on efficiencies of procurement. These factors in combination have created the environment where it has become prevalent for fabricators and/or inspection service companies to interpret and apply the code cases according to their own understanding. This has been observed to have occurred without guidance or experience of working with codes in general, and by people whose native tongue is not English. The situation is not helped by the fact that the Code Cases have not been very well written or presented. In the author’s experience, this has led to situations where any ambiguities of interpretation tend to swing markedly towards the interests of the fabricator and/or inspector, often to the detriment of the end‐ client or purchaser of the plant requiring inspection. The consequential effects of this can be very costly in the longer term due to project delays, remediation cost and other project risks. It is suggested that the situation could be improved through stricter control, both in terms of initial specification of the procurement of NDT processes, but also tighter control throughout the fabrication process. The costs associated with quality assurance are very small compared to the project risk involved. The potential benefits of Ultrasonic Testing (UT) in Lieu of Radiographic Testing (RT) for production welding There are certain potential advantages of UT in lieu of RT during the fabrication process. Here is an overview of the more immediate benefits [see also Ref 6]: i. ii. iii. iv.

No radiation hazard – personnel can work in and around the inspection area No requirement to transport pressure vessels/pipe spools to radiographic compounds Speed. The inspection is completed in a shorter timeframe Potential for improved quality of welding. If applied at the front‐end of a project, it can be used at the weld procedure and welder qualification stage to optimise the welding process, hence minimising the likelihood of repair. See Figure 1.

Depth & positioning information provided. Unlike RT, precise repair co‐ordinates can be provided, minimising the possibility of re‐repairs through missed flaws

Other, less obvious benefits include: i. ii.

The data forms a fingerprint for comparison with future in‐service inspection data. The acceptance criteria of the code cases are in many cases more forgiving in terms of acceptable flaw size. This also reduces the repair frequency, and is especially the case for volumetric welding flaws.

Figure 1. Example of TOFD data taken from a B31.3 CC181 project. The indications scattered throughout the weld body were termed by the welders as ‘fish‐eyes’. These are small lack of fusion flaws that form at the weld bevel faces as the welding head weaves across the weld body. They are a form of combined lack of inter‐run and side‐wall fusion that can be aligned in the axial direction, but also could potentially extend vertically by linking between weld passes. By adjusting the well time at each end of the ‘weave’, this flaw type (which was not detectable radiographically) was eliminated. Note also the interesting ID fit‐up and stop‐start interruption in the weld root penetration – all useful feedback for the design and welding engineers! Taken in combination, the benefits in terms of project cost, quality, duration and risk can be very significant indeed. There have been cases where 24‐hour working (as opposed to fabrication during the day and RT at night) enabled project durations to be halved, but conversely, where UT used in

lieu of RT has been impacted by lack of planning and oversight, delays and costs have been seen to escalate massively, potentially leading to litigation. Disadvantages of UT in lieu of RT i. Certain geometric features present restrictions for UT, e.g. attachments, skirts or nozzles adjacent to welds in the case of pressure vessels, or fittings in the case of piping systems. ii. Variations in expertise – more capable service inspection companies/fabricators will engineer solutions to many, if not all ultrasonic ‘test restrictions’. Others readily give up and seek dispensation to exclude certain welds on the grounds of difficult geometry. It may be permissible to use the ‘test restriction’ excuse in the case of fabrication QC, but not in the case of FFS based on fracture mechanics principles. Inspections should be planned properly to minimise and/or deal with these effects. Fabricators/service inspection companies should be vetted during the pre‐qualification process to assess their ability to deal with these situations. iii. Certain flaw types are difficult to detect with UT (e.g. excess root penetration). iv. Certain materials are not suited to inspection by UT, especially coarse‐grained austenitic stainless steels. v. The fracture‐mechanics‐based acceptance criteria of the code cases become more onerous for thin‐wall materials and the benefits become diminished with wall thickness. Common mis‐interpretations or mis‐applications of the Code Cases Procedures – The purpose and intent of ultrasonic testing procedures themselves is very frequently mis‐understood. A procedure should be derived from the construction code (in this case Section V, Article 4), incorporating the requirements of the code, but reflecting the equipment in use and the specific items to be examined. Work instructions/method statements and check‐lists/calibration records should be defined in the procedures that are required to be used as living documents as each contract progresses. As the codes are intended to be used across a wide range of designs and situations, there is a certain degree of flexibility embodied within them. The American Society for Non‐destructive testing (ASNT) personnel certification scheme SNT‐TC‐1A or CP‐189 as referenced by the codes defines competency levels for individuals to be able to interpret the codes sufficiently to extract the information required in order to construct a procedure. It is common practice however, for fabricators and service inspection contractors to cut and paste blocks of text directly from the codes into their company procedures. Classic examples include code requirements for ‘an ultrasonic test frequency range of 1MHz to 5MHz’, or ‘two beam angles to be selected from 45°, 60° or 70°’ to be repeated word for word in the procedure. This leaves the actual inspection open to interpretation and inconsistencies will occur. These are simplistic examples that lead to relatively minor discrepancies. The requirement to generate a procedure according to ASME V, Art 4, T‐421 (and T III‐422 in the case of TOFD and/or T IV‐422 for Phased Array), including the identification and control of essential and non‐essential variables is generally misunderstood, especially “the requirement for the procedure to establish a single value, or range of values, for each requirement”. This entire section has been observed to have been pasted verbatim directly into a procedure. Much more serious cases are prevalent. As an example, the code cases stipulate that the ultrasonic examination shall include a volume of material to be included on each side of the weld

(the actual distance is dictated by the material thickness). The distance may be reduced to cover only the weld, Heat Affected Zone (HAZ) +6mm of base material, provided “The extent of the weld HAZ is measured and documented during the weld qualification process” and, “The UT transducer positioning and scanning device is controlled using a reference mark....”. It has been observed practice that the text is often lifted directly from the code case to the procedure – and then ignored. The end effect is that inadequate material is examined. Very often, procedures are documents that are generated for audit purposes and technicians performing the work never see them or are even unaware of their existence. QA/QC: Quality standards have developed quite strongly in recent years and there has been a strong focus on reliance on adherence to accredited schemes at the expense of technical audit, specification and supervision. In former times, certifying authorities employing personnel with technical knowledge and experience used to provide this form of oversight. Current QA/QC processes ensure that procedures are adhered to at the system level rather than digging into the technical detail. A key failing of this process is that QA/QC representatives tend to have competencies in QA/QC rather than in NDT. This does not detract from the highly important function of QA/QC as a process, but there is a competency gap that is currently not addressed. Ultrasonic inspection to Section V, Article 4: The code cases do not stipulate which of the techniques described in Article 4 should be used. Conventional pulse‐echo UT (fixed beam), Phased Array (PA) and the Time‐Of‐Flight‐Diffraction (TOFD) techniques are all described and the user is free to select which of these may be used. The criteria of the code cases are that whichever technique is used, it must meet or exceed the minimum qualification criteria of the Code Case. It is unlikely that a conventional pulse‐echo technique will meet the sizing criteria as these are more suited to techniques that make use of the tip‐diffraction process such as TOFD and/or PA. Many of the factors that apply to interpretation and application of the code cases apply equally to interpretation and application of the base code itself, but this will not be addressed here unless it specifically relates to application of the Code Case. TOFD Supplementary coverage (as required by Article 4, Mandatory Appendix III): a) Transverse flaws. An angle beam examination is required for transverse flaws “unless the referencing Code Section requires a TOFD examination. In these cases, position each TOFD probe pair essentially parallel to the weld axis and move the probe pair along and down the weld axis. If the weld reinforcement is not ground smooth, position the probes on the adjacent plate material as parallel to the weld axis as possible.” Caution: The requirement to perform TOFD scans with the beam oriented parallel to the weld axis will not increase the probability of detection for transverse flaws any more than a scan with the beam oriented across the weld, possibly less so. This rationale stems from pulse‐echo UT and does not apply to TOFD in the same way. Although the classic depiction of TOFD is where a crack is perpendicular to the ultrasonic beam, diffracted signals are still generated at the tips of transverse cracks when the crack’s primary axis is oriented parallel to the TOFD beam. An example is shown in Section V, Article 4, Non‐Mandatory Appendix N. The code is wrong on this point, which does not help matters. b) Supplemental shear wave examination. When TOFD is used, Article 4 calls for supplemental shear wave examinations due to the presence of the lateral wave and back‐

wall signals. Comment: Unless the detection and sizing accuracies using these techniques can be successfully qualified using a qualification block(s), the supplemental shear wave examination techniques should be used in conjunction with the ‘good workmanship’ acceptance criteria of Section VIII. This is often overlooked in practice. Qualification block(s): This is possibly the most universally misunderstood section of either of the Code Cases. The block(s) is (are) required to be manufactured by welding or the Hot Isostatic Process (HIP). The author has no experience of the latter being used for fabrication of entire qualification blocks, although this process has been seen to have been used in the nuclear industry to manufacture individual flaws of very precise dimensions. In this case the flaws are created by spark eroding the required flaw dimensions into one or both faces of two blocks of steel. The size of the blocks is somewhat larger than the introduced flaw. The (un‐eroded) mating faces of the two blocks are then bonded together through the application of intense heat and pressure, creating a homogenous piece of material except for the now embedded, intended flaw. The block is then machined into a ‘bobbin’, which is implanted into the qualification block by welding. It is unlikely that HIP bonding would be used in the non‐nuclear industry as there are other, less costly, if less precise methods of simulating planar flaws in welds. Reference to this fabrication process however, has led to speculation that blocks need not be welded, and that artificial flaws may be introduced from the ends of un‐welded qualification blocks (presumably by drilling/Electro‐Discharge Machining (EDM). Discussion of this can be found on www.ndt.net [Ref 7]. The Code Cases carried the statement regarding qualification block(s): “and shall contain a minimum of three flaws, oriented to simulate flaws parallel to the production weld’s fusion line...”. Interpretation of this definition has been carried out in various ways. The author’s interpretation of the intent of this is that the flaws should simulate the most difficult to detect of fabrication flaws in the form of a tight, smooth, planar flaw such as a lack of fusion (in isolation, i.e. not in combination with any other flaw). This is supported by the following statement also posted on the www.ndt.net website: “While the original ASME CC 2235 was not clear on this issue, the intent was to use artificial cracks ‐ not side drilled holes or notches ‐ as the reflectors. In addition, the artificial cracks should follow the bevel to simulate Lack of Fusion defects or similar. ASME is currently working on clarifying this situation. Michael Moles; Member, ASME Section V Ultrasonics Working Group”. It is positive to note that the 2008 Addenda to Section VIII requirements for qualification block flaws now reads: “...and shall contain a minimum of three planar (e.g. crack like) flaws, oriented to simulate flaws parallel to the production weld’s fusion line...”, although B31.3 CC181 still retains the original text. The author’s experience is that where an inspection service contractor or fabricator drives the process, qualification blocks may or may not contain welds, but they will contain drilled holes or notches, whereas where an end‐user drives the process, qualification blocks will always be welded and will usually contain simulated planar welding flaws. The latter fall into the category of “crack‐ like”, in that they are tight, planar and preferentially oriented. Such flaws can be introduced by welding shims onto weld bevel faces (practice required!), or they can be procured from a specialist firm of sample manufacturers. Cases have been observed in practice where 6mm wide buttress notches have been used to represent surface flaws in conjunction with TOFD procedures. This is incorrect on two counts. Firstly, a buttress notch represents a large, strongly reflective area when inspected from the opposite surface (quite unlike any natural planar flaw aligned with the weld fusion line), and

secondly, it is open to the surface. According to Section VIII MT & PT acceptance criteria, linear surface breaking flaws are unacceptable, so there seems little point in qualifying detection and sizing performance for flaws that are not permitted. This does not apply however, to slightly sub‐surface flaws that are classified as surface flaws if the remaining ligament to the external surface is less than half the flaw height. More on this later. Side drilled holes and EDM notches have frequently been observed as artificial flaws in qualification blocks. This generally speaking is a carry‐over from the use of drilled holes and notches in calibration blocks described in Section V, Article 4. In this case, the artificial flaws are intended to create reflectors that are reproducible and easy to manufacture. Their purpose is to control accuracies of calibration, sizing, sensitivity and coverage. The purpose of implanted flaws within qualification blocks is an entirely different matter. Here the onus is not to repeat the calibration process, but to verify the performance of the calibrated UT set‐up on simulated planar welding flaws. It should be borne in mind that a true lack of side wall fusion is often a very tight flaw that has negligible width or gape. In the most extreme of situations, the weld pool may solidify alongside a weld bevel face without actually forming a bond, and in this case it is no more than a molecular separation. Such a flaw will be partially opaque and the tips will have negligible width. Flaw opacity and morphology are both important for pulse‐echo techniques (including phased array), and tip condition is important for techniques that rely on tip diffraction such as TOFD or phased array. Drilled holes and notches satisfy none of these conditions and should not be considered for qualification blocks. A further consideration with qualification blocks is the number of flaws required. The code cases stipulate “a minimum of three planar (e.g., crack like) flaws, oriented to simulate flaws parallel to the weld fusion line. The minimum criteria of only ‘three flaws’ tends to be the automatic choice in practice, and in the author’s view, this is likely to be inadequate in most, if not all cases. However, there are two alternative interpretations to this requirement: i. ii.

the requirement for one flaw at each surface and one sub‐surface flaw is to demonstrate overall system performance through the full thickness, or, the requirement to demonstrate system performance covering each depth zone as described in Section V Article 4, for all bevel angles.

In practice, fabricators and inspection service companies will opt for i. above, but would end‐users be more comfortable with qualifying system performance throughout each zone and bevel angle? Another factor which is widely ignored is the qualification block geometry. Table T‐421 of ASME V, Article 4, 2008 Addenda provides mandatory requirements for UT examinations. This table defines ‘essential variables’ for which a single value or range of values are to be established. It goes on to say that “when procedure qualification is required by the referencing Code Section, a change of a requirement in Table T‐421 identified as an essential variable from the specified value, or range of values, shall require requalification of the written procedure.” The code does not specify the required calibration block geometry, although the 2008 Addenda to Section VIII does state that the qualification block must be within 25% of the thickness to be examined. It follows however, that if the component geometry limits defined in the procedure (essential variable according to T‐412) are exceeded, then additional qualification block(s) will be required. This translates to a requirement for

multiple calibration blocks covering the full range of thicknesses to be examined, material combinations and component geometries. Other factors influenced by price/productivity pressures Welding quality. As stated earlier, a 39mm long by 4mm high subsurface flaw would be acceptable in a 50mm thick pressure vessel or pipe weld. Based on observations in the field it is suspected that some welders or fabricators, on realising that it would in fact be hard to produce a flaw of these dimensions, would be inclined to concentrate on quantity rather than quality. This is especially the case if they are incentivised on the basis of production. This is compounded by the fact that in theory at least, unlimited quantities of volumetric flaws are permitted. NDT technician competencies. Large numbers of technicians have been required by industry to work in accordance with the code cases and there has been a tendency to rush these through the certification process. This has been achieved by streamlining the training, examination and certification process to concentrate on simplistic, clear‐cut and unrealistic flaw conditions. Non‐ Mandatory Appendix N of Section V, Article 4 (TOFD Interpretation) could be construed as misleading in this regard. Very clear‐cut examples of classic flaw interactions are described. The surface‐breaking flaw for example, is a notch, not a real fusion flaw or crack, which behave very differently. Complete loss of lateral wave signal is a very, rare event. The Appendix implies that TOFD indications can be identified, characterised and sized from the TOFD data alone. In extreme cases this is sometimes possible, but they really are rare occurrences. In real‐life, TOFD indications need to be investigated using additional TOFD scanning and/or pulse‐echo techniques to differentiate planar from volumetric flaws based on their reflectivity. Please see Figure 2 as an example of complex flaw formations.

mm 0

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0.0 13.8 19.9 24.8 29.0 32.7 36.3 39.6 42.7 45.7 48.7

Figure 2. TOFD Data ‐ Complex flaw formations, possibly arising as a result of abuse of the relaxed acceptance criteria of the Code Cases, but leading to difficulties with interpretation for the operator trained on clear‐cut, idealistic flaws. This is an example of what occurs regularly in the field. In this case it is manual welding, and is the result of poor workmanship. It probably comprises of a combination of slag inclusions, porosity, lack of side‐wall and lack of inter‐run fusion. The possibility of cracking cannot be discounted, but under the fracture‐mechanics‐based acceptance criteria, flaw type is immaterial, only flaw dimensions are required for acceptance purposes. In the author’s experience, provision is not made for either manual or automated pulse‐echo characterisation (discrimination between planar and volumetric flaws) of complex flaws and this situation is not addressed by codes, standards or procedures. Codes and training materials do however, refer to buried flaws being recognisable due to phase reversals, and far‐surface flaws being identifiable due to effects at or after the back‐wall. In the author’s experience, these idealistic situations do not arise in practice. The only way to deal with the above condition is a combination of advanced signal processing and comprehensive (and time consuming) evaluation by an experienced technician conversant with both pulse‐echo and TOFD. Similar limitations apply to phased array, where complex interactions can occur with direct and mode‐ converted responses from complex flaw formations where ‘masking’ can also be an issue. There is a danger of an inexperienced technician being trained to only look for ‘tops & bottoms’ or back‐wall effects as evidence of planar flaws. This is a potentially dangerous situation, and it should be dealt with early on in the production process. Several cases have been experienced where similar conditions were exposed only after all welding/fabrication was completed. Conclusions It can be concluded that there are significant disparities between the manner in which code case inspections are, or could be applied in practice. On the one hand, the process can be applied in the spirit with which it was intended, possibly with enhancements that enable component quality to be optimised, and on the other, the code cases can be interpreted to deliver lowest project cost, but with highest risk. It can also be concluded that if applied in the spirit with which they are intended, the code cases can lead to a requirement for a large quantity of costly qualification blocks and high levels of qualification activity, which could have the potential to impede project timescales. Although more time and expense should certainly be incurred in this area than is current practice, there are ways in which to manage this process efficiently. This is elaborated further in the next section. Where there is insufficient attention to pre‐qualification and technical supervision throughout the project, successful bidders for construction NDT projects are likely to be those that provide a minimalist interpretation of code case requirements that lead to unacceptable project risks for the end‐user.

Recommendations It is recommended that the following process is adopted in the case of new‐construction projects where ultrasonic examination is carried out in lieu of RT (Section VIII, Div 2, Part 7) and/or ASME B31.3 Code Case 181: i.

ii.

iii.

iv. v.

vi. vii.

viii.

ix.

The end‐user to generate a specification of performance criteria for the fabricator/inspector to follow. Simply to state that the inspection must meet code requirements is insufficient. Fabricators and inspection service companies are under intense pressure to meet timescale and cost targets and will adapt their interpretation of codes to meet these ends. Risk assessments should be carried out on tender submissions. These should address factors such as the probability of project over‐runs, expected weld quality, and should be based on reviews of current competencies, demonstrated capabilities, experience and proven track record. Dependency on quality systems alone is inadequate. Technical supervision. A competent technical authority should be engaged to monitor the process from pre‐contract audit through qualification, inspection and final data review. This should also involve independent review of data to assess quality and reliability of interpretation. It should be contractually agreed that the inspection body is responsible for work that is technically non‐compliant with provision for repeat and/or escalation of inspection activity. The design of qualification blocks, including the type of artificial flaw should be defined in the project specification and approved by the technical authority prior to project commencement. Qualification blocks should reflect actual component geometries, material combinations and wall thicknesses. Qualification flaws should address all inspection zones, flaw orientations (including transverse flaws) and weld bevel angles. Procedures, training and certification criteria should make provision for interpretation and characterisation of complex flaw formations and should address the ability to accurately measure the ligament of remaining material between a flaw tip and the external surface in the case of near‐surface flaws. The inspection process should commence at the welder and weld procedure qualification stage in order to optimise welding quality in advance of production welding. This should become a hold point. Inaccessible welds. Inaccessible, or partially inaccessible welds are often classified as a ‘test restriction’, and excluded from examination. As described earlier, this could be a matter of convenience. Designs should be reviewed by a technically competent authority prior to commencement of construction. A possible alternative to the requirement for extensive flawed samples is to approach qualification in the spirit of a nuclear industry qualification. ASME codes make provision for variations subject to the agreement of all parties, provided the variations at least meet the minimum code requirements. Qualification is required in the nuclear industry according to ASME XI, Appendix 8, Performance Demonstration [Ref 8]. In this case, the performance criteria of an inspection are defined, and the inspection service contractor is required to qualify equipment, procedures and personnel using a combination of open and blind trials on test samples through an independent body. The European nuclear community established the European Network for Inspection Qualification (ENIQ) [Ref 9] through the

European Joint Research Commission (JRC) as a mechanism to maintain qualification standards whilst minimising the requirement for qualification samples. This is achieved through a vigorous process involving expert judgement/reasoning, mathematical modelling (e.g. CIVA [Ref 10] and UMASIS [Ref 11]) and practical demonstration. Prior experience with qualification may be taken into account. Adoption of this process could enable an initial base‐case to be qualified followed by qualification of variables on a case by case basis. ENIQ was developed by the nuclear community, but it is intended to apply to non‐nuclear applications also. It has been used for several oil industry applications in recent years [Ref 12]. Acknowledgements Thanks are extended to my colleagues, Peter Conlin, Gordon Davidson and Gordon Reid of Sonomatic Ltd, all of whom provided out of hours support by providing material in support of this technical paper. References 1. American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section VIII, Code Case 2235. 1996. 2. American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section V, Article 4, 2009 Addenda. 3. American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section VIII, Division 2, Part 7. 2008 Addenda. 4. American Society of Mechanical Engineers, B31.3 Process Piping Code, Code Case 181. 2007. 5. The Integration of Plant Condition Assessment with Risk Management Programmes. J Lilley. European Conference on NDT, Berlin, Germany. Sept 2006. Ref: We 1.2.5. 6. The Shortening of Project Duration. J. Lilley, G Reid. Middle East Conference on NDT. Bahrain. 1993. 7. Website: http://www.ndt.net/ 8. American Society of Mechanical Engineers. Section XI. Appendix 8. Performance Demonstration. 9. European Network for Inspection Qualification (ENIQ). http://safelife.jrc.ec.europa.eu/eniq/ 10. CIVA: http://www‐ civa.cea.fr/scripts/home/publigen/content/templates/show.asp?P=55&L=EN 11. UMASIS: http://www.tno.nl/content.cfm?context=markten&content=case&laag1=190&item_id=444 &Taal=2 12. Development, Validation and Execution of the Automated Ultrasonic Testing of a Subsea Pipeline Hot Tap Weld. Malcolm Miller. Shell UK Ltd. World Conference on NDT. Beijing. 2008.

SINCE 2013 Singapore International NOT Conference & E x hibition 2013, 19-20 J uly 2013

Use of Phased Array Ultrasonic Testing (PAUT) & Time Of Flight Diffraction (TOFD) in Lieu of Radiography Testing on ASME U Stamp Pressure Vessel fabrication Projects P.PUGALENDHI & D.VEERARJU CUTECH PROCESS SERVICES PTE LTD, SINGAPORE ABSTRACT: The Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) technologies have made rapid changes in inspection and reliability in various industries. These ultrasonic testing techniques are rapidly replacing conventional radiography. A major advantage in replacing RT with PAUT & TOFD is reducing the radiation risks apart from increased probability of detection (POD), production rate and better sizing of the discontinuities. This paper discusses the replacement of RT by PAUT & TOFD on ASME U Stamp pressure vessel fabrication projects. Keywords: Ultrasonic, Phased array, sectorial scan, TOFD, in lieu of radiography Reference Codes: 1) ASME Code Case 2235 for boilers and pressure vessels; ASME Section VIII DIV 1 3) ASME Section VIII DIV 2 2)

2. INTRODUCTION Prevention of disasters is a major concern in any industry. Nondestructive testing as a reliable tool has played an effective and important role in this regard. Conventional Ultrasonic testing of heavy wall thickness pressure vessels is a common practice. Due to the increasing demand for more thorough inspection of pressure vessels, researchers have begun looking into more innovative means of defect measurement. Principally, the Phased Array Ultrasonic Testing (PAUT) & Time-Of-Flight Diffraction (TOFD) flawdetection procedure has been implemented to achieve good results and this

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combination shown to be an effective procedure for size and location determination of a discontinuities. Specifically, this combination was proven that this is more suitable for thick structures (above 13mm). Today, the PAUT & TOFD procedure is used for operational inspections or quality control of structures during production instead of routine radiography and conventional ultrasonic shear wave procedures. Although TOFD is more often utilized for inspecting welds with simple geometry and fine grain steels, such as welds with thicknesses from 13 mm to 300 mm, it is useful in inspecting more complex geometries. Defects like cracks, lack of penetration, lack of fusion, porosity, and slag in welds of pressure vessels could be diagnosed via this technique very precisely. Major components in the vessels are Nozzles which are difficult to do Radiography. Nozzles are also pressure retaining parts of the reactors. Even small discontinuities can weaken the containment strength of a pressure vessel. Nozzle types can be identified as either "set on" or "set through" nozzles. Set-on nozzles have the secondary cylinders (i.e. the nozzle) prepared with the weld bevel, and set-through have the primary vessel prepared with the bevel. ASME Code Case 2235 allows for the substitution of Phased Array (PAUT) & Time of flight diffraction (TOFD) in lieu of radiography for the examination of heavy wall pressure vessel welds & Nozzles accordance with ASME Section I, para.PW-11; Section VIII Division 1, para.UW-11 (a); Section VIII Division 2, Table AF-241.1; This paper discusses the advantages of the ultrasonic examination by PAUT and TOFD over radiography and summarizes the code requirements. The most suitable technique for the complete volume coverage of heavy wall thickness & Nozzle joints and coverage of the weld and heat affected zone would be combined phased array ultrasonic testing (PAUT) and TOFD together which also meet the code (ASME Code Case 2235, ASME Section VIII DIV 1 & DIV 2) requirements. Analysis of the acquired Data is done using Tomoview software and evaluation done in accordance with code case. Finally, a computerised report summarizes the results of the examination. This paper explains the successful implementation of PAUT in lieu of RT on ASME U Stamp Pressure vessel fabrication project carried out at the workshop of one of our client.

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3. Radiography Testing (RT) Verses Automated Ultrasonic Testing (AUT -PAUT & TOFD) Radiography has been practiced as the primary non-destructive testing technique for examining heavy wall pressure welds for decades. The requirements of radiography are well known and documented by the ASME code. Manual UT has been used to locate size and confirm the indications found in radiography testing. In thinner wall vessels, radiography is most suitable for detecting both volumetric and planar Indications. The difficulties arise when the wall thicknesses begins to increase and the signal to noise ratios of these typical small indications found by radiography quickly and inherently begins to diminish. This occurs simply due to increasing volume of the weld metal and the heat affected zone. Field experience with automated UT done as per code requirements has shown consistent performance without any reduction in signal to noise ratio even with increasing weld thicknesses. More importantly, the ultrasonic data can measure with a high degree of certainty the through wall I two dimension of an indication. This added dimension along with the length and location of an indication allows for very clear interpretation of the accept/reject criteria as per the ASME code. Other advantages: •

Regulations for the use of Radiography are tight involving special precautions like additional lead or concrete radiation shields, radiation monitoring and evacuation of the construction site to do the radiographic testing. This causes a lot of time delay and costs a lot. Secondly, the work has to be stopped to make the exposures on heavy walled vessels. For AUT, we need not clear the area because of no hazards.

•

Like Radiography, in AUT we can characterize the indications found to be planar (crack like or lack of fusion) or volumetric (slag, porosity etc). More over AUT provides measurement of the through wall dimension of an indication.

•

Results are instant and can be applied to control the 'welding procedure' and make timely rectifications

•

A single pass examination by a well-designed automated UT system is offering the fastest inspection method today and saves valuable time for Construction Company.

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4. Inspection Methods 4.1 Phased Array Ultrasonic Testing PAUT is an advanced method of ultrasonic testing that has applications in medical imaging and industrial testing. When applied to metals the PAUT image shows a slice view that may reveal defects hidden inside a structure or weld. Phased array uses an array of elements, all individually wired, pulsed and time shifted. A typical user friendly computerized setup calculates the time delays from operator input, or uses a predefined file: test angle, focal distance, scan pattern and so forth. The technique also provides a combination of various scans in the same equipment set-up. B-Scan is a side view, CScan is a top view and the S-Scan is a cross-sectional view. These views can be better understood in the Figure 2. From a practical viewpoint, ultrasonic phased arrays are merely a technique for generating and receiving ultrasound; once the ultrasound is in the material, it is independent of the generating technique. Consequently, many of the details of ultrasonic testing remain unchanged; for example; if 5 MHz is the optimum testing frequency with conventional ultrasonic, then phased arrays would typically Use the same frequency, aperture size, focal length and incident angle. As such, phased arrays offer significant technical advantages over conventional single-probe ultrasonic; the phased array beams can be steered, scanned, swept and focused electronically. â&#x20AC;˘

Electronic scanning permits very rapid coverage of the components, typically an Order of magnitude faster than a single probe mechanical system.

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Beam forming permits the selected beam angles to be optimized ultrasonically by Orienting them perpendicular to the predicted defects, for example Lack of Fusion in welds. Beam steering (usually called sectorial scanning) can be used for mapping Components at appropriate angles to optimize Probability of Detection. Sectorial Scanning is also useful for inspections where only a minimal scanning length is possible. Electronic focusing permits optimizing the beam shape and size at the expected Defect location, as well as optimizing Probability of Detection. Focusing improves Signal-to-noise ratio significantly, which also permits operating at lower pulser voltages.

Overall, the use of phased arrays permits optimizing defect detection while minimizing inspection time. Phased arrays offer significant advantages over traditional radiography of welds as well: No safety hazards Inspection as soon as weld is cool Better defect detection and sizing

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Great flexibility in parameter range Compliant with all known codes Many special techniques are possible.

Recently we have done Phased array Ultrasonic testing in our client site for ASME U stamp pressure vessel where the Authorized Inspector (AI) had approved PAUT for ultrasonic examination of welds and in lieu of RT for thickness over 3". Some of the indications found during the PAUT are shown below.

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Figure 2- PAUT Images

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4.2 Time Of Flight Diffraction Time of Flight Diffraction (TOFD) is an advanced automated computerized UT based NOT technique, used for in-service inspection of welds for heavy walled pressure vessels. TOFD system is capable to scan, store and evaluate flaw indications in terms of height, length and position with greater accuracy and is suitable for weld thickness ranging from 13 mm to 300 mm. The principle and operation of TOFD: The TOFD technique is based on diffraction of ultrasonic waves on tips of discontinuities, instead of geometrical reflection on the interface of the discontinuities. When ultrasound is incident at linear discontinuity such as a crack, diffraction takes place at its extremities in addition to the normal reflected wave. This diffracted energy is emitted over a wide angular range and is assumed to originate at the extremities of the flaw (Fig.3). Scanning is done externally parallel to weld axis using longitudinal wave probes with incidence angle range of 45Â° to 70Â°. When flaw is detected during the scanning, Signals from the upper and lower tips of the flaw are displayed as B I D-Scan image. The conventional UT relies on the amount of energy reflected by the discontinuities

Fig. 3 Principle of Time of Flight Diffraction (TOFD) Legend: 1 -Transmitted wave 2- Reflected wave 3- Through transmitted wave 4 - Diffracted wave at upper crack tip 5 - Diffracted wave at lower crack tip

In addition to energies diffracted by defects, the TOFD method will also detect a surface (lateral) wave travelling directly between the probes and also a back wall echo from energies that reach the back of the test piece without interference from defects. The TOFD technique uses a pair of probes in a transmitter-receiver arrangement (Fig. 4). Page No 7 of 14

Usually longitudinal probes are applied with an angle of incidence range of 45° to 70°. The diffracted signals are received via the receiver probe and are evaluated with the Ultrasonic System. The difference in the flight of the diffracted wave fronts carry the information on the spatial relationship of the tips of the defect and hence the extent of the defect. TOFD method only evaluates diffracted echoes.

Lateral w&.ve

Pipwall Back wall echo

Fig. 4 Transmitter-Receiver arrangement of TOFD

4.3 Combined TOFD and Phased Array Technique It is common in Non-Destructive Testing that one NOT technique does not fit in to fulfill all tasks. For heavy wall weld inspection using TOFD, we also have some inherent issues to overcome. •

•

TOFD has a certain dead zone at the surface (limited detection in HAZ area). And near Back wall also. Additional techniques need to be used to ensure coverage of these areas. As the wall thickness increase, one TOFD transducer pair with proper beam spread and sensitivity is not capable of examining the entire weld volume. So, as the wall thickness increases, multiple TOFD transducer pairs will have to be used.

Therefore, to examine fully, a heavy wall weld in a single pass, we offer a combined Multichannel (TOFD+PAUT), zonal inspection, testing technique. In short, multiple probes or probe combinations are fixed in a bracket in such an order that together they cover the whole volume of the weld. Each probe or probe combination is directed to a certain portion of the weld and together these probe units cover the whole volume of the weld. Probe characteristics are optimized in a way, that all possible weld anomalies are detected with high confidence. This principle is called "zonal discrimination".

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PAUT Typically, a 95 mm heavy wall weld requires 3 TOFD channels- each to cover the top, middle and bottom zone respectively. 3 PAUT channels- one transducer on either side of the weld is required to cover the top surface. Similarly, two more PAUT channels, one on each side of the weld is required to cover the bottom surface. 5. ASME Code Case 2235 Requirements ASME Code Case 2235 allows for the use of ultrasonic examination in lieu of radiography for Pressure Vessels and Power Boilers welds greater than 13 mm wall thickness. The Code Case says the following: "The Ultrasonic examination area shall include the volume of the weld, plus 2 in. on each side of the weld for material greater than 8 in. For material thickness 8 in. or less, the ultrasonic examination area shall include the volume of the weld, plus the lesser of 1 in or ton each side of the weld. Alternatively, examination volume may be reduced to include the actual Heat Affected Zone (HAZ) plus %in. of base material beyond the heat affected zone on each side of the weld, etc." (Where t= the thickness of the weld without any allowable reinforcement.) 5.1 Weld Qualification Block- A weld qualification block of similar weld geometry should be prepared with a top surface defect, a bottom surface defect, and an embedded defect- all defects lying along the weld fusion line.

5.2 Qualification Demonstration - A Qualification demonstration on the qualification block is essential. The qualification targets (Surface and embedded notches) are used to prove the technique. Side drilled holes can also be made and provided in the same block and these targets will be used to set the system sensitivity. Therefore, one single block can also be used at times for qualification work as well as calibration purposes.

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5.3 Technique Demonstration In a performance demonstration in front of an ASME Authorized Inspector (AI), two key issues are important. 1) First, it must be demonstrated that the procedure fulfills all requirements of the relevant paragraphs of the ASME Code Case 2235-10. 2) Second, the performance demonstration must make clear that the examination, exactly following the procedure, is able to detect and size specified artificial defects, and that the acceptance criteria for weld defects as stated by the Code Case can be correctly applied. An ASME authorized inspector must be fully convinced that the inspection procedure confirms to the code case. Minimum requirements is that Qualification Blocks used should have similar weld geometry with minimum specified defects like top surface defect, bottom surface defect, and an embedded defect - all along the weld fusion line. Material composition (P-number grouping) should be alike.

Fig 5: 57 mm & 95 mm thick, Qualification Blo

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6.0 Equipment Details We have used Olympus Omni scan MX 21atest version PAUT & TOFD machine and our motorized scanning device is HSTM FLEX & Manual Mini wheel Encoder.

5.1 PAUT & TOFD Scanner The HSMT-Fiexâ&#x201E;˘ is intended for one axis encoded inspection of circumference welds on pipes of 4.5 in. 00 (114.3 mm) and greater. The scanner comes equipped with four probe holders but can be mounted with a total of eight probes with optional probe holders. Mounted probes can be either phased array or conventional UT for most Âˇ efficient inspections. The major characteristic of the scanner is its capacity to bend in the center. This allows the scanner to fit on smaller pipes and also to bring the force of the spring-loaded arm in the radial direction of the pipes for better stability of the wedge, and therefore, optimum data acquisition. For the same reason, optional probe holders that are installed on the outside of the scanner can also pivot. The HSMT-Fiex also allows one of its side frames to slide. This feature allows having the probes mounted on the outside of the scanner. This provides a configuration that is well-suited for hard-to- reach places such as pipe-to-component welds

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6.0 Flaw Acceptance Criteria The ASME Code Case 2235 presents detailed and analytical requirements for Flaw Acceptance Criteria's in three separate tables : Table 1 - 13 mm to less than 1" THICK WELD Table2-1" to 12"THICKWELD Table 3 - Larger than 12" THICK WELD 7.0 Results PAUT & TOFD on 95 mm Thick Pressure vessel Demonstration block results which is approved by Authorized Inspector (AI)

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8.0 Conclusions The Time Of Flight Diffraction (TOFD) & Phased Array Ultrasonic Techniques (PAUT) are rapid, versatile, reliable and an effective advanced UT based NOT method for inspection of welds especially for heavy walled pressure vessels (both pre-service and in-service) with better flaw detection and accurate evaluation of flaw location and flaw sizing. And also combination of PAUT & TOFD proves that a careful preparation of scan plan with appropriate coverage & angles of PAUT & TOFD can detect all flaws that are probable to occur during the welding, thus increasing the reliability of test despite limitation of not having access from both sides of weld to scan apart from this operators, scan plan, procedure, equipment, accessories such as fixtures, scanners, encoders etc. are needed to be established and validated on a mock up with all probable defects before allowing the same on actual welds. Then only on such complex geometry, RT can be replaced by UT reliably.

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PHASED ARRAYS FOR GENERAL WELD INSPECTIONS Michael MOLES OLYMPUS NDT, Waltham, MA, USA 02453 ABSTRACT Ultrasonic phased arrays have proven to be a very appropriate inspection technique for weld inspections, especially encoded arrays with linear scanning. The flexibility of phased arrays allows them to be tailored to almost any weld profile and predicted defects. Besides showing the normal advantages of phased arrays for welds (high speed, reduced costs, full data storage, increased productivity), the paper will illustrate sample weld inspection Scan Plans and coverage. In addition, some codes have been adapted to the use of phased arrays, so these inspection techniques are effectively controlled and approved. TOFD (Time-Of-Flight Diffraction) can be added for improved detection capability and better sizing. Back diffraction also offers significant benefits for accurate sizing. INTRODUCTION The concept of phased arrays has been around for decades, but only in the last sixteen years can industrial phased arrays (PA) be called â&#x20AC;&#x153;commercialâ&#x20AC;?. The principles of phased arrays are well documented (1, 2) elsewhere. Phased arrays have significant advantages over conventional inspection techniques: flexibility, high speed, lower costs (under many conditions), full data storage for auditing, and significantly increased productivity (for volume inspections). Phased arrays can be used in both manual and encoded fashion, which are two completely different approaches (3). This paper deals with encoded scanning, where the true advantages of phased arrays lie. Manual phased arrays are more similar to conventional ultrasonics. Figure 1 (left) shows a typical instrument. On the right is a screen shot showing multiple groups performing simultaneous scanning with encoders; this helps significantly in fulfilling the various codes. For construction welds, codes are of major importance.

Figure 1: Left, Photo of typical portable phased array instrument. Right, screen shot of multigroup scanning.

In recent years, various codes have been written specifically for phased arrays for weld inspections. These codes have specific requirements for coverage, and for appropriate angles. Typically, the inspection is prepared using a Scan Plan, which shows coverage – or lack of it. Also, the codes cover aspects such as scanning speed, beam coverage, calibration etc. In many cases, the addition of Time-Of-Flight Diffraction (TOFD) has major advantages, and tends to cover where phased arrays are weaker (midwall defects and accurate vertical sizing). LINEAR SCANNING One of the big changes in Automated Ultrasonic Testing (AUT) was the switch from raster scanning (which is very time-consuming) to linear scanning, as shown in Figure 2.

Figure 2: Left, raster scanning. Right, linear scanning along weld. This change required moving from conventional single-channel ultrasonics to either multi-probes, or more recently to phased arrays. The time savings were impressive, often an order of magnitude. CODE REQUIREMENTS The dominant code for weld inspection, both globally and for phased arrays, is ASME, specifically Section V (4). ASME has published five separate Code Cases (5) on phased arrays to cover both manual and encoded scanning, and is working on a PA Mandatory Appendix. These Code Cases specify many of the parameters and requirements for performing phased array inspections, specifically: • All beams must be calibrated, whether S-scan or E-scans • “Essential Variables” must be listed, as normal in ASME • Additional phased array parameters must be documented • A “Scan Plan” is required (see below) • Full data collection is required, as per ASME Code Case 2235 for AUT (6) • 6 dB beam overlap is required for coverage, which refers to both S-scans and Escans • Limited data drop-out is allowed.

There are other conditions, but these are the dominant ones. Other organizations, e.g. the American Petroleum Institute, also approve phased arrays, and follow a similar philosophy. While these rules are general and require some thought on the part of the Level III, they are functional in most cases. Some of the specific advantages of phased arrays will now be illustrated: flexibility, speed, productivity, data storage. FLEXIBILITY As phased arrays use electronic control of the beam, the angles, wave modes, scan patterns and coverage are all controlled by the set-up. Figure 3 shows a typical Scan Plan for a thin-walled weld. Note that a single beam is adequate for thinner walls, but not for thicker walls; this would be determined from the Scan Plan. Figure 4 shows an inspection of a thicker-wall T-weld using two S-scans.

-14.00mm

9.00mm Generated with Eclipse Scientific ESBeamTool2

Figure 3: 9mm Wall using standard 45-70 refracted shear wave S-scan.

Generated with Eclipse Scientific ESBeamTool2

Figure 4: 20mm beveled T-weld using standard 45-70o refracted shear wave S-scans with two standoffs

INSPECTION SPEED AND IMPROVED PRODUCTIVITY While cost data and productivity are normally proprietary information, such data that is available shows that much improved scanning speeds are obtainable. Table 1 compares scan times and productivity from manual UT to radiography to PA (7). Not surprisingly, the latest technology (PA) comes out well in front.

Table 1: Comparisons of small pipe weld inspections times and conditions for manual UT, RT and phased arrays. Similar results have been obtained elsewhere. The net effect, particularly in high wage countries, is that equipment costs are a relatively small fraction of the overall price, but scanning speed is so much higher that PA are definitely cost effective. These benefits occur most clearly when the inspection is on a well-defined geometry and is relatively high volume. FULL DATA STORAGE In some industries, e.g. Oil & Gas, auditing the results is a key issue. Encoded scanning permits full data storage, as defined by code. In addition, the data can be reprocessed afterwards, e.g. for more detailed analysis or for alternative evaluation thresholds. In normal weld inspections, PA collect multiple data channels simultaneously at high speed, so the operator cannot analyze all the data at once. Thus, the best choice is to select suitable channels for monitoring to ensure the scan is progressing OK â&#x20AC;&#x201C; and also to get

preliminary feedback for subsequent analysis. Typically, the TOFD channel works well for monitoring (see below). After scanning, the data can be reprocessed as “top, side, end” views or whatever the contractor or contract specifies. Figure 5 shows an example.

Figure 5: “Top, side, end” view of weld showing defects. SCAN PLANS FOR COVERAGE One of the more important aspects of encoded linear scanning is to ensure that correct coverage of the weld is obtained, including any scanning errors. Conveniently, the arrival of lower cost ray tracing software specifically for weld inspections (e.g. ESBeamTool (8) and Scan Plan (9)) has made the set-up operator’s life much easier. Figure 6 shows an example of a weld set-up that shows inadequate coverage (10). Compare Figure 6 with Figures 3 and 4 for coverage.

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Poorly addressed HAZ area

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Figure 6: Scan Plan from ESBeamTool showing poorly addressed HAZ In addition, bevel incidence angles should be as close to normal as possible. ASME does not specify what these angles should be, but the generally accepted maximum is + 10o – if possible. Figure 7 shows an example of a Scan Plan showing a bevel incidence angle which is perhaps a bit high.

Figure 7: Scan Plan showing high bevel incidence angle in cap area. TIME-OF-FLIGHT DIFFRACTION (TOFD) Diffraction is a general phenomenon in ultrasonics, as normal in wave physics (11). The tips of internal defects will diffract an ultrasound beam; this diffracted beam can then be detected and the arrival time accurately measured. The “standard” TOFD set-up is shown in Figure 8.

Figure 8: Standard TOFD set-up. TOFD normally uses a pitch-catch arrangement with the probes symmetrically spaced across the weld. The wedges are angled to generate wide-angle, longitudinal waves (or Lwaves), since these arrive first and don’t confuse the interpretation. Four types of signals are detected: the Lateral wave; the Backwall reflection; the Reflected wave, and any Tip Diffracted waves from defects. The lateral, backwall and tip-diffracted waves are visible in Figure 8.

TOFD images look like vertical through-sections of the weld. The lateral wave is essentially the OD; the backwall is essentially the ID; and any defects show as tip diffracted signals between these two. Figure 9 shows a typical example of a TOFD scan.

Figure 9: Typical TOFD image showing lateral wave (OD), backwall (ID) and four labelled defects. TOFD images always use gray scale presentations and full RF waveforms to capture the phase information. As such, TOFD does not require a lot of data collection, and is very fast. As shown in Figure 8, signals are identifiable by their phase. The OD and ID have a phase reversal, as do the top and bottom of defects. TOFD is a very powerful technique, and allows good midwall defect detection, accurate sizing of defects using the times of arrival of diffracted signals, defect detection even if defects are mis-oriented or located away from the weld centerline, and rapid linear scanning. In addition, set-up is independent of weld configuration. The limitations of TOFD are mainly the dead zones at the OD and ID, plus the interpretation. Overall, TOFD and phased arrays are extremely complementary, and can be run simultaneously. MECHANICS In general, PA, AUT and TOFD codes accept any scanner that fulfills their requirements. The two basic types are fully automated and semi-automated. Both use holders to keep the arrays at a fixed distance and orientation to the weld; both use encoders to ensure full data collection. Figure 10 shows a typical automated scanner on a pipe weld, and Figure 11 a similar semi-automated scanner, or handscanner.

Figure 10: WeldROVER automated scanner on lab pipe.

Figure 11: Encoded PA handscanner with OmniScan MX SUMMARY Phased arrays have developed well in the last several years, particularly for weld inspections. Codes have been, or are being, developed – particularly through ASME. Mechanics, set-ups and procedures are available. A number of other developments, e.g. ray tracing for Scan Plans, have come on the market. Essentially, the technology is “ready to go”. However, the biggest single limitation still applies – a shortage of trained operators. CONCLUSIONS 1. Phased arrays, particularly portable phased arrays, have come a long way in just a few years, especially for weld inspections. 2. Specifically, weld inspection codes have been developed, particularly by ASME. 3. Other developments, such as ray tracing and weld overlays have been developed to aid inspection and interpretation.

REFERENCES 1. Olympus NDT, “Introduction to Phased Array Ultrasonic Technology Applications – R/D Tech Guideline”, published by R/D Tech (now Olympus NDT), August 2004, www.rd-tech.com 2. Olympus NDT, “Advances in Phased Array Ultrasonic Technology Applications”, Olympus NDT Advanced Practical NDT Series, 2007. 3. J. M. Davis and M. Moles, “Phased Arrays vs. Phased Arrays - Beam Sweeping vs. Encoded Data Collection”, Materials Evaluation Back to Basics, June 2007, page 539. 4. ASME Boiler & Pressure Vessel Code, Section V Article 4. 5. ASME Boiler & Pressure Vessel Code, Section V Article 4. See Code Cases 2541, 2557, 2558, 2599 and 2600. Published by the American Society of Mechanical Engineers. 6. ASME Code Case 2235-9, “Ultrasonic Examination in Lieu of Radiography”, ASME Sections I, VIII and XII, October 11, 2006 7. Keith J. Chizen and Michael Moles, “Phased Array for Piping Inspections Using ASME B31.3”, 4th Middle East Conference on NDR, Bahrain, Dec 1-5, 2007. 8. Eclipse Scientific’s ESBeamTool3, See http://www.eclipsescientific.com/Software/ESBeamTool3/info.html 9. Sonovation’s Scan Plan, See http://www.sonovation.com/ 10. E. Ginzel and M. Moles, “S-scan Coverage with Phased Arrays”, Materials Evaluation, August 2008, P. 810 11. J.P. Charlesworth and J.A.G. Temple, 1989, “Ultrasonic Time of Flight Diffraction”, Research Studies Press.

1. Main Concepts of Phased Array Ultrasonic Technology

This chapter gives a brief history of industrial phased arrays, the principles pertaining to ultrasound, the concepts of time delays (or focal laws) for phased arrays, and Olympus NDTâ&#x20AC;&#x2122;s R/D TechÂŽ phased array instruments. The advantages and some technical issues related to the implementation of this new technology are included in this chapter. The symbols used in this book are defined in the Glossary of Introduction to Phased Array Ultrasonic Technology Applications.

1.1

Historical Development and Industrial Requirements The development and application of ultrasonic phased arrays, as a standalone technology reached a mature status at the beginning of the twenty-first century. Phased array ultrasonic technology moved from the medical field1 to the industrial sector at the beginning of the 1980s.2-3 By the mid-1980s, piezocomposite materials were developed and made available in order to manufacture complex-shaped phased array probes.4-11 By the beginning of the 1990s, phased array technology was incorporated as a new NDE (nondestructive evaluation) method in ultrasonic handbooks12-13 and training manuals for engineers.14 The majority of the applications from 1985 to 1992 were related to nuclear pressure vessels (nozzles), large forging shafts, and low-pressure turbine components. New advances in piezocomposite technology,15-16 micro-machining, microelectronics, and computing power (including simulation packages for probe design and beam-component interaction), all contributed to the revolutionary development of phased array technology by the end of the

Main Concepts of Phased Array Ultrasonic Technology

1990s. Functional software was also developed as computer capabilities increased. Phased array ultrasonic technology for nondestructive testing (NDT) applications was triggered by the following general and specific powergeneration inspection requirements:17-24 1.

Decreased setup and inspection time (that is, increased productivity)

Increased scanner reliability

Increased access for difficult-to-reach pressurized water reactor / boiling water reactor components (PWR/BWR)

Decreased radiation exposure

Quantitative, easy-to-interpret reporting requirements for fitness for purpose (also called â&#x20AC;&#x153;Engineering Critical Assessmentâ&#x20AC;?â&#x20AC;&#x201D;ECA)

Detection of randomly oriented cracks at different depths using the same probe in a fixed position

Improved signal-to-noise ratio (SNR) and sizing capability for dissimilar metal welds and centrifugal-cast stainless-steel welds

Detection and sizing of small stress-corrosion cracks (SCC) in turbine components with complex geometry

Increased accuracy in detection, sizing, location, and orientation of critical defects, regardless of their orientation. This requirement dictated multiple focused beams with the ability to change their focal depth and sweep angle.

Other industries (such as aerospace, defense, petrochemical, and manufacturing) required similar improvements, though specific requirements vary for each industry application.25-29 All these requirements center around several main characteristics of phased array ultrasonic technology:30-31

Speed. The phased array technology allows electronic scanning, which is typically an order of magnitude faster than equivalent conventional raster scanning.

Flexibility. A single phased array probe can cover a wide range of applications, unlike conventional ultrasonic probes.

Electronic setups. Setups are performed by simply loading a file and calibrating. Different parameter sets are easily accommodated by preprepared files.

Small probe dimensions. For some applications, limited access is a major issue, and one small phased array probe can provide the equivalent of multiple single-transducer probes.

Chapter 1

Complex inspections. Phased arrays can be programmed to inspect geometrically complex components, such as automated welds or nozzles, with relative ease. Phased arrays can also be easily programmed to perform special scans, such as tandem, multiangle TOFD, multimode, and zone discrimination.

Reliable defect detection. Phased arrays can detect defects with an increased signal-to-noise ratio, using focused beams. Probability of detection (POD) is increased due to angular beam deflection (S-scan).

Imaging. Phased arrays offer new and unique imaging, such as S-scans, which permit easier interpretation and analysis.

Phased array ultrasonic technology has been developing for more than a decade. Starting in the early 1990s, R/D Tech implemented the concepts of standardization and transfer of the technology. Phased array ultrasonic technology reached a commercially viable milestone by 1997 when the transportable phased array instrument, Tomoscan FOCUS™, could be operated in the field by a single person, and data could be transferred and remotely analyzed in real time. The portable, battery-operated, phased array OmniScan® instrument is another quantum leap in the ultrasonic technology. This instrument brings phased array capabilities to everyday inspections such as corrosion mapping, weld inspections, rapid crack sizing, imaging, and special applications.

1.2

Principles Ultrasonic waves are mechanical vibrations induced in an elastic medium (the test piece) by the piezocrystal probe excited by an electrical voltage. Typical frequencies of ultrasonic waves are in the range of 0.1 MHz to 50 MHz. Most industrial applications require frequencies between 0.5 MHz and 15 MHz. Conventional ultrasonic inspections use monocrystal probes with divergent beams. In some cases, dual-element probes or monocrystals with focused lenses are used to reduce the dead zone and to increase the defect resolution. In all cases, the ultrasonic field propagates along an acoustic axis with a single refracted angle. A single-angle scanning pattern has limited detection and sizing capability for misoriented defects. Most of the “good practice” standards add supplementary scans with an additional angle, generally 10–15 degrees apart, to increase the probability of detection. Inspection problems become more difficult if the component has a complex geometry and a large thickness, and/or the probe carrier has limited scanning access. In order to solve the Main Concepts of Phased Array Ultrasonic Technology

inspection requirements, a phased array multicrystal probe with focused beams activated by a dedicated piece of hardware might be required (see Figure 1-1).

Figure 1-1 Example of application of phased array ultrasonic technology on a complex geometry component. Left: monocrystal single-angle inspection requires multiangle scans and probe movement; right: linear array probe can sweep the focused beam through the appropriate region of the component without probe movement.

Assume a monoblock crystal is cut into many identical elements, each with a pitch much smaller than its length (e < W, see chapter 3). Each small crystal or element can be considered a line source of cylindrical waves. The wavefronts of the new acoustic block will interfere, generating an overall wavefront with constructive and destructive interference regions. The small wavefronts can be time-delayed and synchronized in phase and amplitude, in such a way as to create a beam. This wavefront is based on constructive interference, and produces an ultrasonic focused beam with steering capability. A block-diagram of delayed signals emitted and received from phased array equipment is presented in Figure 1-2.

Chapter 1

Probes

Emitting

Incident wave front

Pulses Trigger

Acquisition unit

Phased array unit

Flaw

Reflected wave front

Receiving

Echo signals

Phased array unit

Flaw

Delays at reception

Acquisition unit

Figure 1-2 Beam forming and time delay for pulsing and receiving multiple beams (same phase and amplitude).

The main components required for a basic scanning system with phased array instruments are presented in Figure 1-3.

Computer (with TomoView software)

UT PA instrument (Tomoscan III PA)

Motion Control Drive Unit (MCDU-02)

Test piece inspected by phased arrays

Phased array probe

Scanner/manipulator

Figure 1-3 Basic components of a phased array system and their interconnectivity.

Main Concepts of Phased Array Ultrasonic Technology

An example of photo-elastic visualization32 of a wavefront is presented in Figure 1-4. This visualization technique illustrates the constructivedestructive interference mentioned above.

Courtesy of Material Research Institute, Canada

Figure 1-4 Example of photo-elastic wave front visualization in a glass block for a linear array probe of 7.5 MHz, 12-element probe with a pitch of 2 mm. The 40Â° refracted longitudinal waves is followed by the shear wavefront at 24Â°.32

The main feature of phased array ultrasonic technology is the computercontrolled excitation (amplitude and delay) of individual elements in a multielement probe. The excitation of piezocomposite elements can generate beams with defined parameters such as angle, focal distance, and focal spot size through software. To generate a beam in phase and with constructive interference, the multiple wavefronts must have the same global time-of-flight arrival at the interference point, as illustrated in Figure 1-4. This effect can only be achieved if the various active probe elements are pulsed at slightly different and coordinated times. As shown in Figure 1-5, the echo from the desired focal point hits the various transducer elements with a computable time shift. The echo signals received at each transducer element are time-shifted before being summed together. The resulting sum is an A-scan that emphasizes the response from the desired focal point and attenuates various other echoes from other points in the material. â&#x20AC;˘

At the reception, the signals arrive with different time-of-flight values, then they are time-shifted for each element, according to the receiving focal law. All the signals from the individual elements are then summed

Chapter 1

together to form a single ultrasonic pulse that is sent to the acquisition instrument. The beam focusing principle for normal and angled incidences is illustrated in Figure 1-5. â&#x20AC;˘

During transmission, the acquisition instrument sends a trigger signal to the phased array instrument. The latter converts the signal into a high voltage pulse with a preprogrammed width and time delay defined in the focal laws. Each element receives only one pulse. The multielement signals create a beam with a specific angle and focused at a specific depth. The beam hits the defect and bounces back, as is normal for ultrasonic testing.

Delay [ns] Delay [ns] PA probe

PA probe

Resulting wave surface

Figure 1-5 Beam focusing principle for (a) normal and (b) angled incidences.

The delay value for each element depends on the aperture of the active phased array probe element, type of wave, refracted angle, and focal depth. Phased arrays do not change the physics of ultrasonics; they are merely a method of generating and receiving. There are three major computer-controlled beam scanning patterns (see also chapters 2â&#x20AC;&#x201C;4): â&#x20AC;˘

Electronic scanning (also called E-scans, and originally called linear scanning): the same focal law and delay is multiplexed across a group of active elements (see Figure 1-6); scanning is performed at a constant angle and along the phased array probe length by a group of active elements, called a virtual probe aperture (VPA). This is equivalent to a conventional ultrasonic transducer performing a raster scan for corrosion mapping (see Figure 1-7) or shear-wave inspection of a weld. If an angled wedge is used, the focal laws compensate for different time delays inside the wedge. Direct-contact linear array probes may also be used in electronic angle scanning. This setup is very useful for detecting sidewall lack of fusion or inner-surface breaking cracks (see Figure 1-8). Main Concepts of Phased Array Ultrasonic Technology

Figure 1-6 Left: electronic scanning principle for zero-degree scanning. In this case, the virtual probe aperture consists of four elements. Focal law 1 is active for elements 1â&#x20AC;&#x201C;4, while focal law 5 is active for elements 5â&#x20AC;&#x201C;8. Right: schematic for corrosion mapping with zero-degree electronic scanning; VPA = 5 elements, n = 64 (see Figure 1-7 for ultrasonic display).

Figure 1-7 Example of corrosion detection and mapping in 3-D part with electronic scanning at zero degrees using a 10 MHz linear array probe of 64 elements, p = 0.5 mm.

Chapter 1

Figure 1-8 Example of electronic scanning with longitudinal waves for crack detection in a forging at 15 degrees, 5 MHz probe, n = 32, p = 1.0 mm.

•

Sectorial scanning (also called S-scans, azimuthal scanning, or angular scanning): the beam is swept through an angular range for a specific focal depth, using the same elements. Other sweep ranges with different focal depths may be added; the angular sectors could have different sweep values (see Figure 1-9). The start-and-finish-angle range depends on probe design, associated wedge, and the type of wave; the range is dictated by the laws of physics.

Figure 1-9 Left: principle of sectorial scan. Right: an example of ultrasonic data display in volume-corrected sectorial scan (S-scan) detecting a group of stress-corrosion cracks (range: 33° to 58°). Main Concepts of Phased Array Ultrasonic Technology

â&#x20AC;˘

Dynamic depth focusing (also called DDF): scanning is performed with different focal depths (see Figure 1-10). In practice, a single transmitted focused pulse is used, and refocusing is performed on reception for all programmed depths. Details about DDF are given in chapter 4.

Courtesy of Ontario Power Generation Inc., Canada

Figure 1-10 Left: principle of depth focusing. Middle: a stress-corrosion crack (SCC) tip sizing with longitudinal waves of 12 MHz at normal incidence using depth-focusing focal laws. Right: macrographic comparison.

1.3

Delay Laws, or Focal Laws In order to obtain constructive interference in the desired region of the test piece, each individual element of the phased array virtual probe aperture must be computer-controlled for a firing sequence using a focal law. (A focal law is simply a file containing elements to be fired, amplitudes, time delays, etc.) The time delay on each element depends on inspection configuration, steering angle, wedge, probe type, just to mention some of the important factors. An example of time-delay values in nanoseconds (10-9 s = a millionth part from a second) for a 32-element linear array probe generating longitudinal waves is presented in Figure 1-11. In this image, the detection of side-drilled holes is performed with both negative (left) and positive angles (right). The delay value for each element changes with the angle, as shown at the bottom of this figure.

Chapter 1

Figure 1-11 Example of delay value and shape for a sweep range of 90° (–45° to +45°). The linear phased array probe has 32 elements and is programmed to generate longitudinal waves to detect five side-drilled holes. The probe has no wedge and is in direct contact with the test piece.

Direct-contact probe (no wedge) for normal beam. The focal law delay has a parabolic shape for depth focusing. The delay increases from the edges of the probe towards the center. The delay will be doubled when the focal distance is halved (see Figure 1-12). The element timing has a linear increase when the element pitch increases (see Figure 1-13). For a sectorial (azimuthal) scan without a wedge, the delay on identical elements depends on the element position in the active aperture and on the generated angle (see Figure 1-14). a 140

FD = 15 120

Time delay [ns]

100

FD = 15 FD = 30

FD = 30 60

FD = 60

0 0

Element number

Figure 1-12 Delay values (left) and depth scanning principles (right) for a 32-element linear array probe focusing at 15 mm, 30 mm, and 60 mm longitudinal waves. Main Concepts of Phased Array Ultrasonic Technology

500 450

400

p1 F

p2 > p1 F

Time delay [ns]

350 300 250

Experimental setup L-waves - 5,920 m/s Focal depth = 20 mm Linear array n = 16 elements Delay for element no. 1

200 150 100

50 0.5

p3 > p2

0.75

1.25

1.5

Element pitch [mm]

Figure 1-13 Delay dependence on pitch size for the same focal depth.

1400 LW-no wedge ____F1 = 15 mm _ _ _F2= 30 mm

1200

60º

1000

45º

F2= 2 F1

∆β1

∆β2

Delay [ns]

800

30º 600

400

15º 200

0 1

Element number

Figure 1-14 Left: an example of an element position and focal depth for a probe with no wedge (longitudinal waves between 15° and 60°). Right: an example of delay dependence on generated angle.

Probe on the wedge. If the phased array probe is on a wedge, the delay value also depends on wedge geometry and velocity, element position, and refracted angle (see Figure 1-15). The delay has a parabolic shape for the natural angle given by Snell’s law (45° in Figure 1-16). For angles smaller than the natural angle provided by Snell’s law, the element delay increases from the back towards the front of the probe. For angles greater than the natural angle, the delay is higher for the back 16

Chapter 1

elements, because the beam generated by the front elements follows a longer path in the wedge, and thus the front elements have to be excited first.

Figure 1-15 Example of delay value and its shape for detecting three side-drilled holes with shear waves. The probe has 16 elements and is placed on a 37° Plexiglas® wedge (natural angle 45° in steel).

800

60 degrees 700

30 degrees

F1 F2= 2 F1

Time delay [ns]

600 500

F15/60 F30/60 F15/45 F30/45 F15/30 F30/30

400 300 200

45 degrees ∆β

100 0 0

Element number

Figure 1-16 Example of delay dependence on refracted angle and element position for a phased array probe on a 37° Plexiglas® wedge (H1 = 5 mm).

Delay tolerances. In all the above cases, the delay value for each element must be accurately controlled. The minimum delay increment determines the maximum probe frequency that can be used according to the following ratio:

Main Concepts of Phased Array Ultrasonic Technology

n â&#x2C6;&#x2020;t delay = --fc

[in microseconds, Âľs]

(1.1)

where: n

= number of elements

= center frequency [in MHz]

The delay tolerances are between 0.5 ns and 2 ns, depending on hardware design. Other types of phased array probes (for example, matrix or conical) could require advanced simulation for delay law values and for beam feature evaluation (see chapter 3).

1.4

Basic Scanning and Imaging During a mechanical scan, data is collected based on the encoder position. The data is displayed in different views for interpretation. Typically, phased arrays use multiple stacked A-scans (also called angular B-scans) with different angles, time of flight and time delays on each small piezocomposite crystal (or element) of the phased array probe. The real-time information from the total number of A-scans, which are fired at a specific probe position, are displayed in a sectorial scan or S-scan, or in a electronic B-scan (see chapter 2 for more details). Both S-scans and electronic scans provide a global image and quick information about the component and possible discontinuities detected in the ultrasonic range at all angles and positions (see Figure 1-17).

Courtesy of Ontario Power Generation Inc., Canada

Figure 1-17 Detection of thermal fatigue cracks in counter-bore zone and plotting data into 3-D specimen. 18

Chapter 1

Data plotting into the 2-D layout of the test piece, called corrected S-scans, or true-depth S-scans makes the interpretation and analysis of ultrasonic results straightforward. S-scans offer the following benefits: â&#x20AC;˘

Image display during scanning

â&#x20AC;˘

True-depth representation

â&#x20AC;˘

2-D volumetric reconstruction

Advanced imaging can be achieved using a combination of linear and sectorial scanning with multiple-angle scans during probe movement. S-scan displays, in combination with other views (see chapter 2 for more details), lead to new types of defect imaging or recognition. Figure 1-18 illustrates the detection of artificial defects and the comparison between the defect dimensions (including shape) and B-scan data after merging multiple angles and positions.

Figure 1-18 Advanced imaging of artificial defects using merged data: defects and scanning pattern (top); merged B-scan display (bottom).

A combination of longitudinal wave and shear-wave scans can be very useful for detection and sizing with little probe movement (see Figure 1-19). In this setup, the active aperture can be moved to optimize the detection and sizing angles.

Main Concepts of Phased Array Ultrasonic Technology

Figure 1-19 Detection and sizing of misoriented defects using a combination of longitudinal wave (1) and shear-wave sectorial scans (2).

Cylindrical, elliptical, or spherical focused beams have a better signal-to-noise ratio (discrimination capability) and a narrower beam spread than divergent beams. Figure 1-20 illustrates the discrimination of cluster holes by a cylindrical focused beam. a

Figure 1-20 Discrimination (resolution) of cluster holes: (a) top view (C-scan); (b) side view (B-scan).

Real-time scanning can be combined with probe movement, and defect plotting into a 3-D drafting package (see Figure 1-21). This method offers:

•

High redundancy

•

Defect location

•

Accurate plotting

•

Defect imaging

Chapter 1

â&#x20AC;˘

High-quality reports for customers and regulators

â&#x20AC;˘

Good understanding of defect detection and sizing principles as well the multibeam visualization for technician training

Courtesy of Ontario Power Generation Inc., Canada

Figure 1-21 Example of advanced data plotting (top) in a complex part (middle) and a zoomed isometric cross section with sectorial scan (bottom).35 Main Concepts of Phased Array Ultrasonic Technology

1.5

Limitations and Further Development of Phased Array Ultrasonic Technology Phased array ultrasonic technology, beside the numerous advantages mentioned at the beginning of this chapter, has specific issues listed in Table 1-1, which might limit the large-scale implementation of the technology.33 Table 1-1 Limitations of phased array ultrasonic technology and Olympus NDT’s approaches to overcome them. Issue

Equipment too expensive

Specific details Hardware is 10 to 20 times more expensive than conventional UT.

Olympus NDT approach • Miniaturize the hardware design, include similar features as conventional ultrasonics

Expensive spare parts

• Standardize the production line

Too many software upgrades— costly

• Price will drop to 2–8 times vs. conventional UT. • Limit software upgrades • Issue a probe design guideline, a new book on PA probes and their applications

Require simulation, compromising • Standardize the probe the features manufacturing for welds, Probes too expensive corrosion mapping, forgings, with long lead delivery Price 12 to 20 times more expensive than conventional and pipelines probes • Probe price should decline to 3 to 6 times the price of conventional probes. • Set up training centers with A multidisciplinary technique, different degrees of with computer, mechanical, Requires very skilled ultrasonic, and drafting skills certification/knowledge, and operators with specialized courses Manpower a big issue for largeadvanced ultrasonic • Issue books in Advanced scale inspections knowledge Practical NDT Series related to Basic training in phased array is phased array applications missing. • Develop and include calibration wizards for instrument, probe, Multiple calibrations are required and overall system for probe and for the system; Calibration is time• Develop devices and specific consuming and very periodic checking of functionality setups for periodic checking of must be routine, but is taking a complex system integrity large amount of time. • Standardize the calibration procedures

Chapter 1

Table 1-1 Limitations of phased array ultrasonic technology and Olympus NDT’s approaches to overcome them. (Cont.) Issue

Data analysis and plotting is timeconsuming

Specific details

Redundancy of defect data makes the interpretation/analysis time consuming. Numerous signals due to multiple A-scans could require analysis and disposition. Data plotting in time-based acquisition is time-consuming.

Method is not standardized

Olympus NDT approach • Develop auto-analysis tool based on specific features (amplitude, position in the gate, imaging, echo-dynamic pattern) • Develop 2-D and 3-D direct acquisition and plotting capability34-35 (see Figure 1-21 and Figure 1-22) • Use ray tracing and incorporate the boundary conditions and mode-converted into analysis tools • Active participation in national and international standardization committees (ASME, ASNT, API, FAA, ISO, IIW, EN, AWS, EPRI, NRC)

• Simplify the procedure for Phased array techniques are calibration difficult to integrate into existing standards due to the complexity of • Create basic setups for existing this technology. codes Standards are not available. • Validate the system on open/blind trials based on Procedures are too specific. Performance Demonstration Initiatives36-37 • Create guidelines for equipment substitution • Prepare generic procedures

Compared to the time-of-flight-diffraction (TOFD) method, phased array technology is progressing rapidly because of the following features: •

Use of the pulse-echo technique, similar to conventional ultrasonics

•

Use of focused beams with an improved signal-to-noise ratio

•

Data plotting in 2-D and 3-D is directly linked with the scanning parameters and probe movement.

•

Sectorial scan ultrasonic views are easily understood by operators, regulators, and auditors.

•

Defect visualization in multiple views using the redundancy of information in S-scan, E-scans, and other displays offers a powerful imaging tool.

•

Combining different inspection configurations in a single setup can be used to assess difficult-to-inspect components required by regulators.

Main Concepts of Phased Array Ultrasonic Technology

Figure 1-22 shows an example of the future potential of phased arrays with 3-D imaging of defects.

Figure 1-22 Example of 3-D ultrasonic data visualization of a side-drilled hole on a sphere.34

Olympus NDT is committed to bringing a user-friendly technology to the market, providing real-time technical support, offering a variety of hands-on training via the Olympus NDT Training Academy, and releasing technical information through conferences, seminars, workshops, and advanced technical books. Olympus NDT’s new line of products (OmniScan® MX 8:16, 16:16, 16:128, 32:32, 32:32–128, TomoScan FOCUS LT™ 32:32, 32:32–128, 64:128, QuickScan™, Tomoscan III PA) is faster, better, and significantly cheaper. The price per unit is now affordable for a large number of small to mid-size companies.

Chapter 1

References to Chapter 1 1. 2. 3. 4.

8. 9. 10.

11.

12.

13. 14.

15.

16.

Somer, J. C. “Electronic Sector Scanning for Ultrasonic Diagnosis.” Ultrasonics, vol. 6 (1968): pp. 153. Gebhardt, W., F. Bonitz, and H. Woll. “Defect Reconstruction and Classification by Phased Arrays.” Materials Evaluation, vol. 40, no. 1 (1982): pp. 90–95. Von Ramm, O. T., and S. W. Smith. “Beam Steering with Linear Arrays.” Transactions on Biomedical Engineering, vol. 30, no. 8 (Aug. 1983): pp. 438–452. Erhards, A., H. Wüstenberg, G. Schenk, and W. Möhrle. “Calculation and Construction of Phased Array UT Probes.” Proceedings 3rd German-Japanese Joint Seminar on Research of Structural Strength and NDE Problems in Nuclear Engineering, Stuttgart, Germany, Aug. 1985. Hosseini, S., S. O. Harrold, and J. M. Reeves. “Resolutions Studies on an Electronically Focused Ultrasonic Array.” British Journal of Non-Destructive Testing, vol. 27, no. 4 (July 1985): pp. 234–238. Gururaja, T. T. “Piezoelectric composite materials for ultrasonic transducer applications.” Ph.D. thesis, The Pennsylvania State University, University Park, PA, USA, May 1984. Hayward, G., and J. Hossack. “Computer models for analysis and design of 1–3 composite transducers.” Ultrasonic International 89 Conference Proceedings, pp. 532– 535, 1989. Poon, W., B. W. Drinkwater, and P. D. Wilcox. “Modelling ultrasonic array performance in simple structures.” Insight, vol. 46, no. 2 (Feb. 2004): pp. 80–84. Smiths, W. A. “The role of piezocomposites in ultrasonic transducers.” 1989 IEEE Ultrasonics Symposium Proceedings, pp. 755–766, 1989. Hashimoto, K. Y., and M. Yamaguchi. “Elastic, piezoelectric and dielectric properties of composite materials.” 1986 IEEE Ultrasonic Symposium Proceedings, pp. 697–702, 1986. Oakley, C. G. “Analysis and development of piezoelectric composites for medical ultrasound transducer applications.” Ph.D. thesis, The Pennsylvania State University, University Park, PA, USA, May 1991. American Society for Nondestructive Testing. Nondestructive Testing Handbook. 2nd ed., vol. 7, Ultrasonic Testing, pp. 284–297. Columbus, OH: American Society for Nondestructive Testing, 1991. Krautkramer, J., and H. Krautkramer. Ultrasonic Testing of Materials. 4th rev. ed., pp. 194–195, 201, and 493. Berlin; New York: Springer-Verlag, c1990. DGZfP [German Society for Non-Destructive Testing]. Ultrasonic Inspection Training Manual Level III-Engineers. 1992. http://www.dgzfp.de/en/. Fleury, G., and C. Gondard. “Improvements of Ultrasonic Inspections through the Use of Piezo Composite Transducers.” 6th Eur. Conference on Non Destructive Testing, Nice, France, 1994. Ritter, J. “Ultrasonic Phased Array Probes for Non-Destructive Examinations Using Composite Crystal Technology.” DGZfP, 1996.

Main Concepts of Phased Array Ultrasonic Technology

17. Erhard, A., G. Schenk, W. Möhrle, and H.-J. Montag. “Ultrasonic Phased Array Technique for Austenitic Weld Inspection.” 15th WCNDT, paper idn 169, Rome, Italy, Oct. 2000. 18. Wüstenberg, H., A. Erhard, G. Schenk. “Scanning Modes at the Application of Ultrasonic Phased Array Inspection Systems.” 15th WCNDT, paper idn 193, Rome, Italy, Oct. 2000. 19. Engl, G., F. Mohr, and A. Erhard. “The Impact of Implementation of Phased Array Technology into the Industrial NDE Market.” 2nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, New Orleans, USA, May 2000. 20. MacDonald, D. E., J. L. Landrum, M. A. Dennis, and G. P. Selby. “Phased Array UT Performance on Dissimilar Metal Welds.” EPRI. Proceedings, 2nd Phased Array Inspection Seminar, Montreal, Canada, Aug. 2001. 21. Maes, G., and M. Delaide. “Improved UT Inspection Capability on Austenitic Materials Using Low-Frequency TRL Phased Array Transducers.” EPRI. Proceedings, 2nd Phased Array Inspection Seminar, Montreal, Canada, Aug. 2001. 22. Engl, G., J. Achtzehn, H. Rauschenbach, M. Opheys, and M. Metala. “Phased Array Approach for the Inspection of Turbine Components—an Example for the Penetration of the Industry Market.” EPRI. Proceedings, 2nd Phased Array Inspection Seminar, Montreal, Canada, Aug. 2001. 23. Ciorau, P., W. Daks, C. Kovacshazy, and D. Mair. “Advanced 3D tools used in reverse engineering and ray tracing simulation of phased array inspection of turbine components with complex geometry.” EPRI. Proceedings, 3rd Phased Array Ultrasound Seminar, Seattle, USA, June 2003. 24. Ciorau, P. “Contribution to Detection and Sizing Linear Defects by Phased Array Ultrasonic Techniques.” 4th International NDE Conference in Nuclear Ind., London, UK, Dec. 2004. 25. Moles, M., E. A. Ginzel, and N. Dubé. “PipeWIZARD-PA—Mechanized Inspection of Girth Welds Using Ultrasonic Phased Arrays.” International Conference on Advances in Welding Technology ’99, Galveston, USA, Oct. 1999. 26. Lamarre, A., and M. Moles. “Ultrasound Phased Array Inspection Technology for the Evaluation of Friction Stir Welds.” 15th WCNDT, paper idn 513, Rome, Italy, Oct. 2000. 27. Ithurralde, G., and O. Pétillon. “Application of ultrasonic phased-array to aeronautic production NDT.” 8th ECNDT, paper idn 282, Barcelona, Spain, 2002. 28. Pörtzgen, N., C. H. P. Wassink, F. H. Dijkstra, and T. Bouma. “Phased Array Technology for mainstream applications.” 8th ECNDT, paper idn 256, Barcelona, Spain, 2002. 29. Erhard, A., N. Bertus, H. J. Montag, G. Schenk, and H. Hintze. “Ultrasonic Phased Array System for Railroad Axle Examination.” 8th ECNDT, paper idn 75, Barcelona, Spain, 2002. 30. Granillo, J., and M. Moles. “Portable Phased Array Applications.” Materials Evaluation, vol. 63 (April 2005): pp. 394–404. 31. Lafontaine, G., and F. Cancre. “Potential of Ultrasonic Phased Arrays for Faster, Better and Cheaper Inspections.” NDT.net, vol. 5, no. 10 (Oct. 2000). http://www.ndt.net/article/v05n10/lafont2/lafont2.htm.

Chapter 1

32. Ginzel, E., and D. Stewart. “Photo-Elastic Visualization of Phased Array Ultrasonic Pulses in Solids.” 16th WCNDT, paper 127, Montreal, Canada, Aug 29– Sept. 2004. 33. Gros, X. E, N. B. Cameron, and M. King. “Current Applications and Future Trends in Phased Array Technology.” Insight, vol. 44, no. 11 (Nov. 2002): pp. 673– 678. 34. Reilly D., J. Berlanger, and G. Maes. “On the use of 3D ray-tracing and beam simulation for the design of advanced UT phased array inspection techniques.” Proceedings, 5th International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, San Diego, USA, May 2006. 35. Ciorau, P., W. Daks, and H. Smith. “A contribution of reverse engineering of linear defects and advanced phased array ultrasonic data plotting.” EPRI. Proceedings, 4th Phased Array Inspection Seminar, Miami, USA, Dec. 2005. 36. Maes, G., J. Berlanger, J. Landrum, and M. Dennis. “Appendix VIII Qualification of Manual Phased Array UT for Piping.” 4th International NDE Conference in Nuclear Ind., London, UK, Dec. 2004. 37. Landrum, J. L., M. Dennis, D. MacDonald, and G. Selby. “Qualification of a Single-Probe Phased Array Technique for Piping.” 4th International NDE Conference in Nuclear Ind., London, UK, Dec. 2004.

Main Concepts of Phased Array Ultrasonic Technology

PAUT,TOFD,AUT In Lieu of RT

Pars Leading Inspection Co. Presented By: Behrouz Piranfar

9/10/2013

Techniques

Time Of Flight Diffraction (TOFD)

Contents

     

How it works Typical TOFD Display Defect Analysis Defect Example Application Advantage

Principle of TOFD

Transmitter

Receiver Lateral wave Upper tip Lower tip

Back-wall reflection ď&#x192;&#x2DC; Time-Of-Flight Diffraction (TOFD) relies on the diffraction of ultrasonic energies from 'corners' and 'ends' of internal structures (primarily defects) in a component being tested using a set of two probes.

How it works

DEFECT

PROBE

Reflection

Back

How it works

DEFECT

PROBE

Diffraction

How it works

DEFECT

Diffraction

How it works

Practically

How it works

Lateral wave + Pos

Amplitud dB

Tiemper ms

- Neg

How it works

Signal Diffracted

+ Pos

Amplitud dB

Tiemper ms

- Neg

How it works

Reflection From Back wall

+ Pos

Amplitud dB

Tiemper ms

- Neg

How it works

Data Collection 6 5 4 3 2 1 Rx

How it works

Phase Reversal + Pos

Amplitude dB

- Neg

Time = Âľ seconds or Millimetres

How it works

Greyscale Image Presentation

Depth

Lenght

Typical TOFD Display

Defect Analysis with Cursors

ď&#x192;&#x2DC; Use of cursors on top and bottom of defect to size the defect

Example – Near–Surface Breaking Defect

Lateral wave blocked Sizing by measuring crack tip

Example – Mid-wall Defect  No break in lateral wave or back wall  Top and bottom signals visible (if defect deep enough)  Can measure lengths using hyperbolic cursors

Example – Lack of Root Penetration

 Sometimes see break in back wall signal  Defect can be sized using time-of-arrival  Similar to other root defects

Example – Lack of Sidewall Fusion

 Should see no perturbations in lateral wave or Back wall  In this case, top signal is “buried” in lateral (OD) wave  Can size easier if signals are clear.

Example - Porosity

ď&#x192;&#x2DC; Multiple small reflectors, each with hyperbolic tails. Usually can characterize, but sizing difficult.

Example â&#x20AC;&#x201C; Transverse Cracks

ď&#x192;&#x2DC; Transverse cracks are rare, and similar to porosity, No perturbation of lateral or back wall

Example – Internal Lack of Fusion

•

Strong signal but height measurement difficult

Applications  Critical plant items in construction and in-service  Pressure Systems – Vessels, pipelines, pipe-work  Storage facilities – Tanks, spheres  Tube Vessels - Boilers, Heat Exchangers, Condensers  High Temperature Inspection Up to 480˚C

 Service induced defects & structural damage  Corrosion/erosion profiling - especially weld root erosion  Thick wall components > 300mm  Clad/lining interface bond/cracking

TOFD Advantages 

Excellent POD for mid-wall defects



Good detection of miss oriented defects



Can characterize surface-breaking defects



Excellent sizing for defects in transverse



Tolerable sizing for defects in linear mode



Works very well in conjunction with pulse-echo



Rapid (and relatively low cost) inspections



Permanent Record of All Parameters



Offline Interpretation and Measurement



Excellent Repeatability.

Challenges



Dead zone of ~3mm at outer surface



Additional B-scans necessary for transverse positioning



Hard to interpret



Difficult to apply to thin materials (<6mm)



Combine with MUT for exact location of defect

Techniques

Phased Array Ultrasonic Test (PAUT)

Contents

          

How it works Scan view Sectorial scan Electronic scan Scan plane Software Indication example Application Advantage Code Equipments

How it works  A NEW ultrasound NDT technology borrowed from medical  An “Array” of transducers elements in which the timing of elements’ excitation can be individually controlled to produce certain desired effects, such as steering the beam axis or focusing the beam  Each element has its own connector, time delay circuit and A/D converter  Elements are acoustically insulated from each other

 Elements are pulsed in groups with precalculated time delays for each element; “Phasing”

How it works  Transmission (Tx)  Elements pulsed at controlled time intervals  Control of beam direction and focusing  The delays are known as Tx Focal Laws

Beam Steering

Beam Focusing

How it works

 Reception (Rx)  RF waveforms received by each element are delayed, then averaged  Delays used to align the signals = Rx Focal Laws

•Ultrasound reflects from defect –Elements receive ultrasound at different times due to the different beam paths –Signals then aligned by electronic circuitry

Scan view

Sectorial scan

Multiple Focal Laws

 Beam is swept through many angles  Wide coverage of the specimen Side Drilled Holes

Back wall

Electronic scanning Each PRF cycle  Aperture moves through the length of the array  No raster movement required  Full volumetric coverage achieved

scanning

 Physical scan movement in one axis only  Full axial weld coverage achieved

Scan Plane

ď&#x192;&#x2DC;Definition of specimen and weld geometry, coverage assessment using linear scan PAUT and representation of a typical PAUT and TOFD combination

Software A-Scan, E-Scan, and C-Scan, END View

Software Sectorial Scan, Top view , TOFD

Flaw Volumetric Position Overview  Flaw volumetric position is defined as the position of the flaw relative to the weld or component.  For weld inspection it is typically expressed as negative or positive in relation to the weld centerline or weld reference, and either embedded, connected to the ID, or connected to the OD. The flaw volumetric position is a key indicator for determining what SWLF flaw on weld overlay type of defect has been detected. (Slag, porosity, IP, LOF, ext.)  Knowledge of the weld bevel and weld process is extremely helpful. In a V weld, IP would occur in the Sk90 (-) Sk270 (+) bottom root area, obviously. In a X weld IP would occur in the weld center.  Regardless if volumetric position Weld is a requirement of the referencing Centerline code, knowing the volumetric position is necessary to make the repair. Where to excavate and how deep and long?

Flaw Volumetric Position - Overlay  Weld overlays are the primary indicator for determining volumetric flaw position.  Using the part and weld wizard almost any symmetrical or asymmetrical weld can be created and displayed on the S-scan.

 The weld overlays should be considered close approximations when used to determine flaw location. The overlay is dependent on the scanner or manual probe position being maintained or entered with a high level of precision for them to be useful. Slag

Inadequate penetration

OD connected crack

Root crack

Porosity

Inclusion

Lack of root fusion

Case Study  Present day NDT methodology utilizes radiography is the main method with a double wall double image technique to check the integrity of these weld joints.  Natural weld defects were included in 3 pipes of 44.5 mm of diameter and 5 mm thickness with a single V configuration such as: – (i) toe crack and lack of incomplete penetration in Pipe-1 – (ii) root crack and lack of side wall fusion in Pipe-2 – (iii) an individual porosity and cluster porosities were introduced in Pipe-3  The three pipe samples were subjected to radiography and the results were analyzed  The samples were also inspected utilizing the COBRA Phased Array system

Case Study

 The defects are

Toe Crack

– Toe crack – Incomplete penetration Incomplete penetration

Case Study

Root Crack

 These defects are – Root crack – Lack of side wall fusion

LOF

Case Study

 The defects are – isolated porosity – Cluster of porosities Cluster Porosity

Applications  Pressure vessels  Pipelines  Portable weld inspections  Raw material production: ingots, billets, bars…

 Aircraft: civil and defence: In-Service Inspection  Military Pre-Service Inspection & In-Service Inspection  Power Generation: nuclear & fossil fuel: In-Service Inspection  Petrochemical: pipeline construction welds  Applications can be on anything currently applying pulse-echo testing

Corrosion Mapping

 Compatible with Phased array  Detection of corrosion, erosion, pitting, etc.  2 in long array probe for fast acquisition

 A scans acquisition  Use of water box couplant efficiency

improves

Pressure Vessels  Low cost and easy to use  Can use conventional or PA  Uses TOFD and pulse-echo  Good approach for very thick walls

 Need allowance for operator error  Simplest mechanical solution  No safety hazard, no delays  Can use magnetic wheel scanner

Pipelines

 AUT gives much better inspection: better detection, better resolution  MUT is significantly worse, due to unfocused beams and inappropriate angles

 RT and MUT would reject many more welds

Austenitic Piping ď&#x192;&#x2DC; PA instrument, two 5MHz 16 element probes using a splitter/umbilical, and a mechanical scanner.

1.5mm hole on near side of the weld

High Temperature Inspection

 Inspection with specific probe and wedge can be carried out at high temperature in many situations.  Detection and sizing up to 400˚C

Phased array weld inspection

Sample calibration Block

Construction Welding Sample crack and S-scan image

Corner Crack  Inspection with 40- to 70-degree refracted angle  Real-time display of S-scan and A-scan

Bolts PA Probe Threads

15 Degree Beam 15 Degree Beam

Notch #1

Notch #1 0 Degree Beam 360 Groove

360 Groove

Mode Conversions Notch #2

Notch #2 End of Bolt 0 Degree Beam

End of Bolt

PA Sectorial Scan

Boiler

 High Volume – Typically large number of welds to inspect  Many different configurations (diameter, thickness, etc)

Advantages

One probe covers many angles Can produce compression and shear wave No radiation hazard, chemicals and films, equipment inside pipe

Great resolution High speed inspection Instantaneous recording and evaluation of results Provides immediate feedback to the welders Reproducibility

Codes Some quick comments  ASME is the most widely used code.  Specifically accepts phased arrays (as do most codes) as a technology, but the techniques and procedures need to be developed.  Normal procedure is to demonstrate these through a Performance Demonstration, e.g. Appendix 14 or CC 2235 in the case of ASME.

Codes  Three manual code cases: CC 2451for single angle scanning, CC 2557 for manual S-scans, manual E-scans (2558)  Two code cases for encoded linear scans: – linear E-scans (2599), and – linear S-scans (2600).

Codes ď&#x192;&#x2DC; A Standard Guide for setting up PA is available (E-2491-06) ď&#x192;&#x2DC; This SG requires full angular compensated gain (ACG) and TCG over the side-drilled hole calibration range for S-scans.

Equipments TD-Handy Scan

Veo-Sonatest

OmniScan® MX 2

Equipments OmniScan® MX 2 With hundreds of units being used throughout the world, the OmniScan MX is Olympus NDT’s most successful portable and modular phased array and eddy current array test instrument. The OmniScan family includes the innovative phased array and eddy current array test modules, as well as the conventional eddy current and ultrasound modules, all designed to meet the most demanding NDT requirements. The OmniScan MX offers a high acquisition rate and powerful software features—in a portable, modular instrument—to efficiently perform manual and automated inspections.

Equipments Veo-Sonatest The veoâ&#x20AC;&#x2122;s robust design, intuitive user interface and extensive online help brings the power of Phased Array to the field based technician. The powerful veo platform unlocks a new level of performance in a portable instrument. The Inspection Plan shows the operator in 2D and 3D where probes are positioned on the test part, simplifying the inspection setup and providing an inspection reference for reporting. Multiple scans from different probes may be displayed and evaluated at the same time. Multiple Sectorial scans, top, side and end view extractions plus C scans are all supported by the veo. TOFD and Phased array inspections can be carried out in tandem at full scanning speed and with up to 2GB data files large areas can be inspected more efficiently. Full resolution waveform data is stored directly to a removable USB data key for ease of back up and transfer to PC.

Equipments TD-Handy Scan

TD-Handy scanÂŽ Is a new hand-held multifunction advanced ultrasonic used system, the TD-Handy scanÂŽ is most successful portable phased array and TOFD test instrument. The TD-Handy scan allow the phased array and TOFD test simultaneously, and also possible to have strip chart scan which is not available by other portable equipments, all designed to meet the most demanding NDT requirements. The TDHandy scan offers a high acquisition rate and powerful software features in a portable to efficiently perform manual and automated inspections. Although the TD Handy-Scan is a small hand-held instrument weighing only 3.3 kilograms, it sports an impressive battery of features and capability.

Reporting

Techniques

Automated Ultrasonic Test (AUT)

Contents

           

What is AUT? History Calibration Block TOFD Phased Array Mapping Zone Discrimination Equipment AUT Advantage AUT In Iran Codes and standards Conclusion

What is AUT?

ď&#x192;&#x2DC;

The AUT system is used for weld inspection as a combination of two or three different techniques. It provides detailed information on the position, size, and orientation of defects. Using either a conventional multi-probe, or phased array setup, the system scans a weld in a single pass. The operator is then able to view the results in a graphical presentation.

What is AUT? 

The weld thickness is divided into a number of depth zones

 Inspection concept is related to the weld bevel configuration  Full weld inspection coverage is achieved by placing an ultrasonic probe set on both sides of the weld, each probe within the set examines a layer within the weld.

History

Initial AUT design Mid 1960 s

History

 AUT Go-NoGo presentation Mid 1970 s

 AUT paperchart recorder Mid 1980 s

 AUT with PC presentation begin 1980 s

History

 AUT paperchart recorder Mid 1980 s

 Computerized AUT Mid 1990 s

 Computerized AUT end 1990 s

Zone Discrimination

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6

 Weld zoned - inspect with focused waves from both sides. (Up/Down stream)  Fast, reliable weld inspection (ASME/ASTM/API compliant)  Mechanics simpler & more reliable  Conventional UT = 1 probe per zone  Phased Array = 1 probe covers all zones

Zone Discrimination

Tandem probe application

 angle variation  focussing  tandem

Zone 2

Zone Discrimination

Зоны F5 F4 F3 F2 F1

Scan Plane

Calibration Block ď&#x192;&#x2DC; A calibration plate, made of an original piece of the pipeline material to be inspected, is prepared with artificial defects such as flat bottom holes and or notches, which represent actual flaws. ď&#x192;&#x2DC; Artificial defects are present in each depth-zone.

Calibration Block

Capabilities

ď&#x192;&#x2DC; For application of the AUT, it is good practice to operate strictly according to a mutually agreed inspection procedure. To judge the results, the procedure always contains clear acceptance/rejection criteria. These criteria may be based on an Engineering Critical Assessment or Good Workmanship Standards.

ď&#x192;&#x2DC; Using 3 main methods (TOFD, Phased Array, Mapping) together to achieve better and more accurate results.

TOFD

A-scan

Indication

Lateral wave

Back-wall

Phased array

Probe angle

Flat bottom hole focus

Mapping ď&#x192;&#x2DC; The mapping feature enables the system to visualise the presence of the geometrical welding features such as the position of the weld cap and root penetration, which minimises the possibility of the system generating false calls. Furthermore this feature enables the system to cope with most existing UT procedures and acceptance criteria, because of its capability to detect and, to a certain extent, quantify volumetric defects.

Mapping

Advantages of mapping:

 Increase of inspection integrity  Reducing of false calls  Characterization of defects  Can be combined with pulse-echo technique

TOFD , Phased array

TOFD , Phased array ď&#x192;&#x2DC; Phased array inspection techniques are often complimented with TOFD. ď&#x192;&#x2DC; TOFD is particularly beneficial for increased length and depth sizing accuracy to compliment amplitude based pulse-echo inspections. Data displayed in Tomoview 2.9 for offline analysis. Volume merge C-scan and TOFD B-scan.

Zone Discrimination •Phased array, ToFD, Pulse echo •Easy UT set-up and configuration •Configure for code complience •Meets requirements of EN 1712, API 1104, DNV 2000 FS101, ASTM E1961 •Automated or manual data evaluation •Built in reporting

Zone Discrimination

Recording Threshold

Shaded area shows TOF

Colours indicate Above / Below Acceptance thresholds

Amplitude Data

Data from Up-stream Channels

Data from

Threshold

Down-stream channels

breaking defects.

Calibration Block

LOP

LOF

Porosity

TOFD

AUT Advantages Can be used On and Offshore No radiation hazard, No chemicals and films No equipment inside pipe Hot and cold operating temperatures >100 welds/day onshore and>150 welds/day offshore Digital and real-time results, final report on a DVD

High speed inspection, High POD Instantaneous recording and evaluation of results Provides immediate feedback to the welders

AUT Advantages

AUT Equipments

PipeWizard V4

TD-Handy Scan

AUT in Iran 2004 Siri offshore pipeline by Saipem, 83 Km SP 4&5 offshore pipeline by Saipem, 190 Km 2006 Salman (EPC 3) offshore pipeline by IOEC, ~30 Km SP 8 offshore pipeline by Sadra/DOT, 100 km 2007 SP 9&10 offshore pipeline by IOEC, ~190 Km 2008 Siri-Asaluyeh offshore pipeline by IOEC, 282 Km 2009 SP 15 offshore pipeline by IOEC, ~80 Km 2010-2011-2012 SP 12 offshore pipeline by IOEC, ~440 Km Reshadat in field , ~120 Km Forozan in field , ~120 Km SP 15,16 offshore pipeline by IOEC, ~130 Km SP 15 offshore pipeline by IOEC, ~260 Km

AUT in Iran 2013 SP 19 offshore pipeline by IOEC, ~260 Km SP 20,21 ~ In progress

 Total installation of pipelines using AUT in lieu of RT:  ~2200 Km  Range of diameters: 4” To 56”  Range or Thickness: 6mm to 38mm  Working hours/shift: Shifts/day: 2

 Record per shift: 107 welds (32” main line and 4” piggy back)

Codes and standards

 In 1998, the ASTM published the E-1961-98 code (reapproved in 2003), which covers key elements of AUT of girth welds – zone discrimination, rapid data interpretation, specialized calibration blocks, and configuration procedures. The E-1961 code is designed for ECA. Similarly, in 1999, the American Petroleum Institute (API) published the 20th edition of Standard 1104, which covers mechanized ultrasonic testing and radiography of girth welds.  Other codes:

DNV OS-F101, BS 4515-1 2009

 TOFD Acceptance codes: European norms: BS7706 and EN583_6 ASTM E-2373-04 ASME CC 2235-1

RT compare with AUT

Reporting

Thanks for your time!

Please do not hesitate to ask for further information

Unit 7, No 1, Allay 1, Fiyat St,

Ekbatan-Tehran Tel/Fax:

+98-21-44694583

E-mail:

Info@parsinspection.com

Internet:

www.parsinspection.com

PAUT,TOFD,AUT In Lieu of RT

Pars Leading Inspection Co. Presented By: Behrouz Piranfar

9/10/2013

Techniques

Time Of Flight Diffraction (TOFD)

Contents

     

How it works Typical TOFD Display Defect Analysis Defect Example Application Advantage

Principle of TOFD

Transmitter

Receiver Lateral wave Upper tip Lower tip

How it works

DEFECT

PROBE

Reflection

Back

How it works

DEFECT

PROBE

Diffraction

How it works

DEFECT

Diffraction

How it works

Practically

How it works

Lateral wave + Pos

Amplitud dB

Tiemper ms

- Neg

How it works

Signal Diffracted

+ Pos

Amplitud dB

Tiemper ms

- Neg

How it works

Reflection From Back wall

+ Pos

Amplitud dB

Tiemper ms

- Neg

How it works

Data Collection 6 5 4 3 2 1 Rx

How it works

Phase Reversal + Pos

Amplitude dB

- Neg

Time = Âľ seconds or Millimetres

How it works

Greyscale Image Presentation

Depth

Lenght

Typical TOFD Display

Defect Analysis with Cursors

ď&#x192;&#x2DC; Use of cursors on top and bottom of defect to size the defect

Example – Near–Surface Breaking Defect

Lateral wave blocked Sizing by measuring crack tip

Example – Mid-wall Defect  No break in lateral wave or back wall  Top and bottom signals visible (if defect deep enough)  Can measure lengths using hyperbolic cursors

Example – Lack of Root Penetration

 Sometimes see break in back wall signal  Defect can be sized using time-of-arrival  Similar to other root defects

Example – Lack of Sidewall Fusion

 Should see no perturbations in lateral wave or Back wall  In this case, top signal is “buried” in lateral (OD) wave  Can size easier if signals are clear.

Example - Porosity

ď&#x192;&#x2DC; Multiple small reflectors, each with hyperbolic tails. Usually can characterize, but sizing difficult.

Example â&#x20AC;&#x201C; Transverse Cracks

ď&#x192;&#x2DC; Transverse cracks are rare, and similar to porosity, No perturbation of lateral or back wall

Example – Internal Lack of Fusion

•

Strong signal but height measurement difficult

 Service induced defects & structural damage  Corrosion/erosion profiling - especially weld root erosion  Thick wall components > 300mm  Clad/lining interface bond/cracking

TOFD Advantages 

Excellent POD for mid-wall defects



Good detection of miss oriented defects



Can characterize surface-breaking defects



Excellent sizing for defects in transverse



Tolerable sizing for defects in linear mode



Works very well in conjunction with pulse-echo



Rapid (and relatively low cost) inspections



Permanent Record of All Parameters



Offline Interpretation and Measurement



Excellent Repeatability.

Challenges



Dead zone of ~3mm at outer surface



Additional B-scans necessary for transverse positioning



Hard to interpret



Difficult to apply to thin materials (<6mm)



Combine with MUT for exact location of defect

Techniques

Phased Array Ultrasonic Test (PAUT)

Contents

          

How it works Scan view Sectorial scan Electronic scan Scan plane Software Indication example Application Advantage Code Equipments

 Elements are pulsed in groups with precalculated time delays for each element; “Phasing”

How it works  Transmission (Tx)  Elements pulsed at controlled time intervals  Control of beam direction and focusing  The delays are known as Tx Focal Laws

Beam Steering

Beam Focusing

How it works

 Reception (Rx)  RF waveforms received by each element are delayed, then averaged  Delays used to align the signals = Rx Focal Laws

•Ultrasound reflects from defect –Elements receive ultrasound at different times due to the different beam paths –Signals then aligned by electronic circuitry

Scan view

Sectorial scan

Multiple Focal Laws

 Beam is swept through many angles  Wide coverage of the specimen Side Drilled Holes

Back wall

Electronic scanning Each PRF cycle  Aperture moves through the length of the array  No raster movement required  Full volumetric coverage achieved

scanning

 Physical scan movement in one axis only  Full axial weld coverage achieved

Scan Plane

ď&#x192;&#x2DC;Definition of specimen and weld geometry, coverage assessment using linear scan PAUT and representation of a typical PAUT and TOFD combination

Software A-Scan, E-Scan, and C-Scan, END View

Software Sectorial Scan, Top view , TOFD

Inadequate penetration

OD connected crack

Root crack

Porosity

Inclusion

Lack of root fusion

Case Study

 The defects are

Toe Crack

– Toe crack – Incomplete penetration Incomplete penetration

Case Study

Root Crack

 These defects are – Root crack – Lack of side wall fusion

LOF

Case Study

 The defects are – isolated porosity – Cluster of porosities Cluster Porosity

Applications  Pressure vessels  Pipelines  Portable weld inspections  Raw material production: ingots, billets, bars…

Corrosion Mapping

 Compatible with Phased array  Detection of corrosion, erosion, pitting, etc.  2 in long array probe for fast acquisition

 A scans acquisition  Use of water box couplant efficiency

improves

Pressure Vessels  Low cost and easy to use  Can use conventional or PA  Uses TOFD and pulse-echo  Good approach for very thick walls

 Need allowance for operator error  Simplest mechanical solution  No safety hazard, no delays  Can use magnetic wheel scanner

Pipelines

 AUT gives much better inspection: better detection, better resolution  MUT is significantly worse, due to unfocused beams and inappropriate angles

 RT and MUT would reject many more welds

Austenitic Piping ď&#x192;&#x2DC; PA instrument, two 5MHz 16 element probes using a splitter/umbilical, and a mechanical scanner.

1.5mm hole on near side of the weld

High Temperature Inspection

 Inspection with specific probe and wedge can be carried out at high temperature in many situations.  Detection and sizing up to 400˚C

Phased array weld inspection

Sample calibration Block

Construction Welding Sample crack and S-scan image

Corner Crack  Inspection with 40- to 70-degree refracted angle  Real-time display of S-scan and A-scan

Bolts PA Probe Threads

15 Degree Beam 15 Degree Beam

Notch #1

Notch #1 0 Degree Beam 360 Groove

360 Groove

Mode Conversions Notch #2

Notch #2 End of Bolt 0 Degree Beam

End of Bolt

PA Sectorial Scan

Boiler

 High Volume – Typically large number of welds to inspect  Many different configurations (diameter, thickness, etc)

Advantages

One probe covers many angles Can produce compression and shear wave No radiation hazard, chemicals and films, equipment inside pipe

Great resolution High speed inspection Instantaneous recording and evaluation of results Provides immediate feedback to the welders Reproducibility

Equipments TD-Handy Scan

Veo-Sonatest

OmniScan® MX 2

Equipments TD-Handy Scan

Reporting

Techniques

Automated Ultrasonic Test (AUT)

Contents

           

What is AUT? History Calibration Block TOFD Phased Array Mapping Zone Discrimination Equipment AUT Advantage AUT In Iran Codes and standards Conclusion

What is AUT?

ď&#x192;&#x2DC;

What is AUT? 

The weld thickness is divided into a number of depth zones

History

Initial AUT design Mid 1960 s

History

 AUT Go-NoGo presentation Mid 1970 s

 AUT paperchart recorder Mid 1980 s

 AUT with PC presentation begin 1980 s

History

 AUT paperchart recorder Mid 1980 s

 Computerized AUT Mid 1990 s

 Computerized AUT end 1990 s

Zone Discrimination

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6

Zone Discrimination

Tandem probe application

 angle variation  focussing  tandem

Zone 2

Zone Discrimination

Зоны F5 F4 F3 F2 F1

Scan Plane

Calibration Block

Capabilities

ď&#x192;&#x2DC; Using 3 main methods (TOFD, Phased Array, Mapping) together to achieve better and more accurate results.

TOFD

A-scan

Indication

Lateral wave

Back-wall

Phased array

Probe angle

Flat bottom hole focus

Mapping

Advantages of mapping:

 Increase of inspection integrity  Reducing of false calls  Characterization of defects  Can be combined with pulse-echo technique

TOFD , Phased array

Zone Discrimination

Recording Threshold

Shaded area shows TOF

Colours indicate Above / Below Acceptance thresholds

Amplitude Data

Data from Up-stream Channels

Data from

Threshold

Down-stream channels

breaking defects.

Calibration Block

LOP

LOF

Porosity

TOFD

High speed inspection, High POD Instantaneous recording and evaluation of results Provides immediate feedback to the welders

AUT Advantages

AUT Equipments

PipeWizard V4

TD-Handy Scan

AUT in Iran 2013 SP 19 offshore pipeline by IOEC, ~260 Km SP 20,21 ~ In progress

 Total installation of pipelines using AUT in lieu of RT:  ~2200 Km  Range of diameters: 4” To 56”  Range or Thickness: 6mm to 38mm  Working hours/shift: Shifts/day: 2

 Record per shift: 107 welds (32” main line and 4” piggy back)

Codes and standards

DNV OS-F101, BS 4515-1 2009

 TOFD Acceptance codes: European norms: BS7706 and EN583_6 ASTM E-2373-04 ASME CC 2235-1

RT compare with AUT

Reporting

Thanks for your time!

Please do not hesitate to ask for further information

Unit 7, No 1, Allay 1, Fiyat St,

Ekbatan-Tehran Tel/Fax:

+98-21-44694583

E-mail:

Info@parsinspection.com

Internet:

www.parsinspection.com

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Advanced Ultrasonic Inspection PAUT •

PAUT = Phased Array Ultrasonic Testing

•

Computerized application of ultrasonics in which high speed electronics, real time imaging. With todays advanced technology, special probes are utilized for inspection.

•

There is no physical difference between conventional UT and PAUT. Both use the same basics and theory

•

The main difference between conventional UT and PAUT is within the probe

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Advanced Ultrasonic Inspection PAUT

• •

A mosaic of transducer elements

• •

Elements' excitation can be individually controlled

Basically PAUT probe is a conventional probe cut into many elements

Certain desired effects can be produced by timing the elements excitation  steering the beam axis  focusing the beam.

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Advanced Ultrasonic Inspection PAUT

How does it work

• • •

Elements are acoustically insulated from each other Elements are pulsed in groups with pre calculated time delay for each element Focal law: defines the elements to be fired, time delays, and voltages for both the transmitter and receiver functions.

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Advanced Ultrasonic Inspection PAUT

Beam Forming

•

No time delay applied

•

PAUT probe becomes like a conventional UT probe

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Advanced Ultrasonic Inspection PAUT

Beam Steering

•

Provides capability to modify refracted angle

•

Allows for multiple angle inspection using a single probe

•

Applies a linear focal law (delays)

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Advanced Ultrasonic Inspection PAUT

Beam Steering

•

Provides capability to modify refracted angle

•

Allows for multiple angle inspection using a single probe

•

Applies a linear focal law (delays)

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Advanced Ultrasonic Inspection PAUT

Beam Focusing and Steering at the same time

• •

Provides capability to Focus at a certain depths and at a chosen range of different angles Applies a focal law (delays) as in below figure

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Advanced Ultrasonic Inspection PAUT

Electronic scanning

•

The ability to move the beam along one axis of an array without any mechanical movement

•

The movement is performed only by time multiplexing the active element group

•

The beam movement depends on the probe geometry and could be:  linear scanning  sectorial scanning  lateral scanning  combination

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Advanced Ultrasonic Inspection PAUT

Linear electronic scan

•

The beam will move along the length of the probe

•

Can be straight beam or a beam at a fixed angle

•

This type of scan is often used for corrosion mapping applications

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Advanced Ultrasonic Inspection (PAUT)

Sectorial scan

•

The ability to scan a complete sector or volume without any probe movement

•

Useful for inspection of complex geometries

•

This is the most typical scan which distinguishes phased array from other techniques

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Advanced Ultrasonic Inspection PAUT

Applications

• • • • •

New construction weld inspection In-service weld inspection including Stress Corrosion Cracking Complex Geometries – Nozzles, Flanges, Shafts, bolts C-Scan mapping AUT is also commonly used, accepted, and code compliant with phased array ultrasonics

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Advanced Ultrasonic Inspection PAUT

Weld inspection

• •

A scan plan to make sure the weld is covered completely is made first The scan plan will assist in setting up equipment and focal laws

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Advanced Ultrasonic Inspection PAUT

Weld inspection

•

Equipment calibration

   

Velocity Wedge delay for all angles Sensitivity for all angles Time Corrected Gain (TCG)

Weld scanning  Manually  Semi –automated, using an encoder and fixed distance to weld center line  Using a semi-automated or completely automated scanner

•

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Advanced Ultrasonic Inspection PAUT

Inspection Results

•

Signal interpretation  On Omni scan  Using Tomo view

Interpretation can be preformed in the field “real time” and also reviewed post inspection. Permanent data files can be saved for future resource. Commonly used for monitoring and also Auditing inspection results

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Advanced Ultrasonic Inspection PAUT Advantages & Disadvantages

Advantages

•

Gives information about lateral position of defect in weld (depth and height)

•

Gives a permanent record

•

Repeatability, good for monitoring

•

No radiation involved

•

Can be used for several applications

•

Can find defect at surface and in volume of weld (no dead zone)

•

Interpretation simplified

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Disadvantages

•

Higher cost equipment required

•

Requires experienced and trained technician for interpretation

•

Angle of incidence is not always optimal when using S-scan

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How Can We Help?

Contact Tim Shaw Chief Marketing Officer Email : info@dacon-inspection.com Mobile Phone : +66 (0) 89 245 9966 www.dacon-inspection.com

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NDT.net - The e-Journal of Nondestructive Testing (October 2008) For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=25

Phased Array Ultrasonic Technology (PAUT) Contribution to Detection and Sizing of Microbially Influenced Corrosion (MIC) of Service Water Systems and Shut Down Coolers Heat Exchangers in OPG CANDU Stations Peter Ciorau 1, Lou Pullia 1, Trek Hazelton 1, Wence Daks 2 1

OPG-IMS, Pickering, Canada, Email: peter.ciorau@opg.com lou.pullia@opg.com trek.hazelton@opg.com 2 CAD WIRE, Markham, Canada, Email: wence@cadwire.com ABSTRACT Three PAUT techniques [linear scan – longitudinal waves, sector scan –longitudinal waves and sector scan-transverse waves] were developed and validated to assess the MIC attack in service water systems (SWS) and shutdown coolers heat-exchangers (SDC-HX) of Darlington and Pickering CANDU stations. PAUT employs linear array probes with a frequency between 4-12 MHz, depending on surface conditions, component geometry and MIC size/category to be detected. Examples from lab validation and field trials are presented. Based on field trials results, the techniques were optimized and new cal blocks were manufactured. It was demonstrated for mid-length pipes and for SDC-HX, the PAUT is the best technique compared with D-meter conventional UT and with guided waves. The expected field accuracy is about 0.5 mm (0.020”) for large MIC attack. The ligament evaluation is technically achievable for colonies / pin holes located 2 mm under the outer surface. Improvements were identified and implemented for the next outages. KEYWORDS: microbially influenced corrosion (MIC), service water system piping, shutdown cooler heat exchanger, HAZ, corrosion colonies, PAUT electronic scan, pin hole, dome colony, PAUT azimuthal scan, ligament assessment.

BACKGROUND As service water systems within electrical utilities are supplied by lake water, there is a threat for MIC to occur within certain portions of the plant systems. These are generally isolated to service water systems where conditions of flow and temperature are conducive to MIC attacks. MIC generally occurs randomly with a tendency to attack the heat affected zone (HAZ) of welds (see Figure 1-left). The corrosion defects can take on a few different shapes but are principally conical in nature making it difficult to inspect with conventional ultrasonics. The MIC colonies could lead to forced outages, due to pin hole leaking (see Figure 1-right).

Figure 1: MIC attack on service water systems-elbows; left – radiography of random MIC; right – pin holes leaks detected in an elbow.

Heat exchangers of shut down coolers are attacked by MIC in HAZ of buffer plate weld (see Figure 2). The MIC attack produced costly forced outages.

Figure 2: Examples of MIC attack on HX-SDC lower weld of the buffer plate. In 2002-2003 OPG-IMCS developed conventional ultrasonic procedures for HX-SDC lower weld and SWS piping. These conventional procedures are time-consuming, have difficulty distinguishing inclusions and laminations from MIC attack, and could allow isolated small colonies and pin holes to be undetected. New techniques using PAUT were developed and commissioned for SWS piping and SDCHX. The techniques were field-commissioned during two outages: Pickering Unit 4 in 2006 and Darlington Unit 2-3 in 2007. This paper presents the PAUT advantage in detecting and sizing MIC attack.

PAUT TECHNIQUES

PAUT could employ three techniques in detecting MIC attacks: •

Electronic (linear) scan using longitudinal waves with large probe: is used for a quick assessment of significant domes with height > 1/3 of pipe wall. Can’t detect small colonies and pin holes. The wedge must be adapted to pipe curvature, and scan is performed axially.

•

Sectorial scan using longitudinal waves with high frequency (8-10 MHz) small probes; this technique is capable to detect small MIC colonies with dome height >2 mm. Could assess with mode-converted shear waves the pin holes up to 2 mm (0.080”) to the outer surface.

•

Sectorial scan using shear waves with frequency 4-10 MHz and small probes. This technique is very efficient for pin hole detection, but has errors in height evaluation, namely for shallow domes (h < 2 mm); however this technique can detect deep pin holes with ligaments of 1.2 mm (0.055”) before piercing the outer surface.

The principle of three techniques is presented in Figure 3.

Figure 3: PAUT techniques for MIC attack detection: left - linear scan L-waves; middle â&#x20AC;&#x201C; sectorial scan L-waves: right â&#x20AC;&#x201C; sectorial scan T-waves. The PAUT techniques were validated on retired-for-cause SDC-HX samples (see Figure 4) and on artificial-made MIC defects of different shapes (see Figure 5 to Figure 7).

Figure 4: Detection of two MIC colonies in SDC-HX by S-scan L-waves.

Figure 5: Linear scan on artificial defects (left) and on a MIC colony in HX sample (right).

Figure 6: Different defect types detected by S-scan L-waves.

Figure 7: Different defect types detected by S-scan T-waves.

FIELD APPLICATIONS

Examples of field applications from Pickering SDC- HX inspections are presented in Figure 8 to Figure 10.

Figure 8: Example of PAUT inspection of SDC- HX with L-waves- PNGS U4.

Figure 9: PAUT detection of a MIC attack with ligament of 0.306â&#x20AC;?.

Figure 10: MIC attack location in HAZ of lower weld on HX 4.

Examples of field inspection of DNGS service water lines are presented in Figure 11 to Figure 13.

Figure 11: Examples of field inspection of secondary service water lines at DNGS.

Figure 12: Examples of different MIC attack defects detected by PAUT at DNGS.

Figure 13: Examples of MIC location and data comparison with RT.

CONCLUDING REMARKS

PAUT techniques developed for MIC attack were validated during lab and field trials. PAUT is capable to detect and size different types of MIC attack, with ligaments up to 1.2 mm. The most productive technique is S-scan L-waves, with a direct reading of colony diameter and ligament. This PAUT

technique is also very visual, allowing easy interpretation of the data and has been well received from the inspection technicians. The ligament measurement was improved for near-surface pin holes by using high-resolution filters and delay wedges. Measurements were compared to D-meter and RT and they were found in to be in good agreement. Improvements were identified, including cavitations evaluation near the weld or in the weld root area. PAUT method is efficient for short-range piping, between the valves and on elbows and Tees. PAUT contributed to dose reduction and reliable MIC attack detection on HX-SDC. ACKNOWLEDGEMENTS The authors wish to thank OPG-IMCS Management for granting the publication of this paper in on-line NDT.net journal.

Sridhar Samiyaiah/ Charlie Chong