Ut testing section 9 annexes

Addendum-01 Equipment Calibrations My ASNT Level III UT Study Notes.

2014-June

Normal Beams Calibration Techniques

Attenuation due to Beam spread for:  Large Reflector  Small Reflector

Attenuation Due to Beam Spread: Large Reflector

Attenuation Due to Beam Spread: Small Reflector

SH1 D1

D2 SH2

Material Attenuation Determination:

Material Attenuation Determination: Actual BWE display

IF zero Material attenuation: The second BWE at twice the distance will be exactly 6dB less (50% less), half the 1st BWE height ( ½ FSH). However this is never the case!

Δ dB = total Material attenuation at twice distance travel.

Material attenuation =

ΔdB

D1

D2

Material Attenuation in 100mm = YdB-XdB-6dB Material attenuation in dB/mm = (YdB-XdB-6dB)/100 YdB-XdB-6dB X dB

Y dB

Construction of beam edges plot- Normal Transducer

Construction of Beam Edges:

20dB drop to find edges of beam

The other edge:

Construction of beam spread at 13mm:

Construction of beam spread at 25mm:

Construction of beam spread at 32mm:

Angle Beams Calibration Techniques

Perspex as Matching Layer/Wedge

Tunsten impregnated epoxy resin

θs1

2730m/s

θs2

3250m/s

Perspex as Matching Layer/Wedge 1. The Shear wave velocity of Perspex is 2730m/s, the shear wave velocity od steel is 3250m/s. The refracted angle of Perspex Ď´S1 is always smaller than Ď´S2 2. Pespex is very absortive and attenuated efficiently, thus reflected compressional wavw will be dampen.

First/ Second Critical Angles VL1= 2730m/s, VS2= 3250m/s, VL2= 5900m/s 1st / 2nd critical angle 27.56° 57.14°

Ist Critical angle= 27.56° °

2nd Critical angle= 57.14°

B 33.42°

First/ Second Critical Angles 27.56째

57.14째

째

33.42째

Finding the probe index

Finding the probe index

Checking the probe Angle:

Calibration for range:

Calibration for range:

Angle Beam- Beam edges Proving (Vertical Axis) using IOW Block Stand Off Measurement Techniques.

Stand-off 2 Stand-off 1 Stand off 2

Angle Beam- Beam edges Proving (Vertical Axis) using IOW Block Botoom edge.

Angle Beam- Beam edges Proving (Vertical Axis) using IOW Block Bottom Edge.

The IOW Block: The Institute of Welding Block

The Proofing: Plot out the Stand-Off1 & 2 readings on a transparent slide, superimposed the ploted transparent slide on IOW Block

Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block

Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block

Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block

Scanned at ½ , 1, 1 ½ Skips

Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block

Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block

½ Skip 1 Skip 1½ Skip

The DAC

The DAC

DAC Curve

DAC Curve

DAC Curve Plot 1. Obtained the signal from the refernce reflector and mark on the graticule/traspatrent sheet with gain setting at 80% FSH. 2. Set the gain control -6bB and marks the 50% mark.

3. Set the gain contril to the 4. Obtained the signal at the gain setting in item 1 and repeat the process at different sound paths.

5. Plot the curves at the gain setting and -6dB. 6. Determined the transfer correction.

7. Scanned the work pieces at the “Gain Setting + Transfer Correction�

FLAT Bottom Holes FBH

FLAT Bottom Holes FBH

Reading on: FLAT Bottom Holes FBH

https://www.cnde.iastate.edu/ultrasonics/grain-noise

FLAT Bottom Holes FBH A type of reflector commonly used in reference standards. The end (bottom) surface of the hole is the reflector.E quivalent:, the size of a flat-bottom hole which at the same range, gives an ultrasonic indication equal to the one from the discontinuity. This reflector is used in DGS curves, or many calibration blocks, or standards such as the GE specification.

Transfer Corection

Transfer Correction: Reference surface are smooth and scale free unlike the actual work pieces. These call for transfer correction to account for transfer loss resulting from actual scanning.

Transfer Correction: Reference surface are smooth and scale free unlike the actual work pieces. These call for transfer correction to account for transfer loss resulting from actual scanning.

Transfer Correction: Reference surface are smooth and scale free unlike the actual work pieces. These call for transfer correction to account for transfer loss resulting from actual scanning.

Transfer Correction:

Transfer Correction: Comparison of BWE for Compression Probe

Test Material curve

Gain Setting

Reference Block curve

Transfer correction at thickness

Measured point Beam path

Transfer Correction: Compression Probe Method, Plot a curve of gain setting for FSH at different south paths for actual and reference block, the different in gain control at thickness is the transfer correction.

Transfer Correction: Angle Probes Methos, used 2 eaqual angle probes, pitch and catch in the test material ans using the reference block. The differences in gain setting is the transfer correction,

DGS- Distance Gain Size

http://www.sonostarndt.com/EnProductShow.asp?ID=198

FLAT Bottom Holes FBH â–

DGS/AVG

DGS is a sizing technique that relates the amplitude of the echo from a reflector to that of a flat bottom hold at the same depth or distance. This is known as Equivalent Reflector Size or ERS. DGS is an acronym for Distance/Gain/Size and is also known as AVG from its German name, Abstand Verstarkung Grosse. Traditionally this technique involved manually comparing echo amplitudes with printed curves, however contemporary digital flaw detectors can draw the curves following a calibration routine and automatically calculate the ERS of a gated peak. The generated curves are derived from the calculated beam spreading pattern of a given transducer, based on its frequency and element diameter using a single calibration point.

Material attenuation and coupling variation in the calibration block and test specimen can be accounted for. http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/dgs-avg/

DGS is a primarily mathematical technique originally based on the ratio of a circular probe’s calculated beam profile and measurable material properties to circular disk reflectors. The technique has since been further applied to square element and even dual element probes, although for the latter, curve sets are empirically derived. It is always up to the user to determine how the resultant DGS calculations relate to actual flaws in real test pieces.

An example of a typical DGS curve set is seen below. The uppermost curve (Curve #1) represents the relative amplitude of the echo from a flat plate reflector in decibels, plotted at various distances from the transducer, and the curves below (Curve #2) represent the relative amplitude of echoes from progressively smaller disk reflectors over the same distance scale.

(Curve #1) represents the relative amplitude of the echo from a flat plate reflector in decibels, plotted at various distances from the transducer

(Curve #2) represent the relative amplitude of echoes from progressively smaller disk reflectors over the same distance scale.

As implemented in contemporary digital flaw detectors, DGS curves are typically plotted based on a reference calibration off a known target such as a backwall reflector or a flat bottom hole at a given depth. From that one calibration point, an entire curve set can be drawn based on probe and material characteristics. Rather than plotting the entire curve set, instruments will typically display one curve based on a selected reflector size (registration level) that can be adjusted by the user. In the example below, the upper curve represents the DGS plot for a 2 mm disk reflector at depths from 10 mm to 50 mm. The lower curve is a reference that has been plotted 6 dB lower.

In the screen at left, the red gate marks the reflection from a 2 mm diameter flat bottom hole at approximately 20 mm depth. Since this reflector equals the selected registration level, the peak matches the curve at that depth. In the screen at right, a different reflector at a depth of approximately 26 mm has been gated. Based on its height and depth in relation to the curve the instrument calculated an ERS of 1.5 mm.

(Curve #2) represent the relative amplitude of echoes from progressively smaller disk reflectors over the same distance scale.

More reading on DGS

DGS- Different sizes of FBH at different distance

DGS

# of near field

What is DGS TCG is a time-corrected DAC so that equal dimension reflectors give equal amplitude responses for all sound path distances. Used for PAUT Sectorial scans where it would be otherwise impossible to set every angle and sound path to the same sensitivity level using DAC's.

ASTM E-1316: DGS (distance gain size-German AVG)distance amplitude curves permitting prediction of reflector size compared to the response from a back surface reflection.

The probe manufacturer supplies data sheet diagams for each probe which shows the amplitude response curves from the backwall and a range of diameters of flat-bottom holes along the length of the soundfield.

Have a look at EN 583-2:2001 Sensitivity and range setting for excellent authoritative descriptions of DAC/TCG and DGS. You'll have to look at AWS D1.1. for instance for knowledge of their sensitivity setting requirements.

Knowledge of these techniques is desirable but will such knowledge really improve your inspection method? You use DAC because the Codes and standards you work to require you to assess indications to those DAC's. A report that a reflector was 3,5 mm equivalent FBH size to DGS would most probably be rejected.

DGS-If you have a signal feom a flaw at a certain depth, you can compare the signal of BWE from the FBH at that depth. The defect then could be sized as equivalent of the size of the FBH.

Size 0.24

Size 0.24

2.4depth

http://www.ndt.net/article/berke/berke_e.htm

Locating & Sizing Flaws

Locating reflectors with an angle-beam probe Fig. 53 Scanning a reflector using an angle beam probe The echo of a discontinuity on the instrument display does not now give us any direct information about its position in the material. The only available information for determination of the reflector position is the scale position and therefore the sound path s, this means the distance of the discontinuity from the index point (sound exit point) of the probe, Fig. 53.

The mathematics of the right-angled triangle helps us to evaluate the Surface Distance and the Depth of a reflector which are both important for the ultrasonic test, Fig. 54a. We therefore now have the possibility to instantly mark a detected flaw's position on the surface of the test object by measurement of the surface distance from the sound exit point and to give the depth. For practical reasons, the reduced surface distance is used because this is measured from the front edge of the probe. The difference between the surface distance and the reduced surface distance corresponds to the x-value of the probe, this is the distance of the sound exit point to the front edge of the probe, Fig. 54b.

With ultrasonic instruments having digital echo evaluation these calculations are naturally carried out by an integrated microprocessor and immediately displayed so that the operator does not need to make any more timeconsuming calculations, Fig. 55. This is of great help with weld testing because with the calculation of the flaw depth an additional factor must be taken into account, namely: whether the sound pulses were reflected from the opposing wall. If this is the case then an apparent depth of the reflector is produced by using the depth formula which is greater than the thickness T of the test object. The ultrasonic operator must acertain whether a reflection comes from the opposite wall and then proceed with calculating the reflector depth, Fig. 56b.

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/common-test-practices/

Practice Makes Perfect 81. The 100 mm radius in an IIW block is used to: (a) Calibrate sensitivity level (b) Check resolution (c) Calibrate angle beam distance (d) Check beam angle 80. The 50 mm diameter hole in an IIW block is used to: (a) Determine the beam index point (b) Check resolution (c) Calibrate angle beam distance (d) Check beam angle

Practice Makes Perfect 35. The 2 mm wide notch in the IIW block is used to: (a) Determine beam index point (b) Check resolution (c) Calibrate angle beam distance (d) Check beam angle

Pulse-Echo Instrumentation

The Circuitry:       

Voltage activation of the PE crystal Ultrasound formation Propagation Reflection Charge formation of crystal Processing Display

Pulse-Echo Instrumentation Transmitter

TRX

Receiver Amplifier

Detector

Scan Converter Display

TGC

TGC – Time Gain Compensation Circuit

Pulse-Echo Instrumentation Pulser Components 1. HV pulse generator 2. The clock generator 3. The transducer

Pulse-Echo Instrumentation Generated Wave

Applied Voltage

+

+

V

P TIME

TIME

-

-

Pulse-Echo Instrumentation The Pulser rate is known as the pulse repetition frequency (PRF).

Typical PRF 3,000 – 5,000.

PRF automatically adjusted as a function of imaging depth.

Pulse-Echo Instrumentation Switch that controls the output power of the HV generator is the attenuator.

Pulse-Echo Instrumentation

TRX

PULSER

ATTENUATOR

Pulse-Echo Instrumentation CLOCK GENERATOR Controls the actual number of pulses which activate the crystal.

Responsible for sending timing signal to the 1. Pulse generator 2. TGC circuitry 3. Memory

Pulse-Echo Instrumentation CLOCK GENERATOR

TGC UNIT

HV GENERATOR

MEMORY

TRS

TRX

CRT DISPLAY

Pulse-Echo Instrumentation Sensitivity refers to the weakest echo signal that the instrument is capable of detecting and displaying.

Factors that determine sensitivity are 1.

2.

3.

4.

Transducer frequency Overall and TGC receiver gain Reject control Variable focal zone on array real-time instruments.

Pulse-Echo Instrumentation Increasing the voltage causes 1. Greater amplitude – greater penetration 2. Longer pulses – degrades axial resolution 3. Increase exposure

Pulse-Echo Instrumentation Transducer has dual roles; transmitting and receiving signals.

The transducer is capable of handling a wide range of voltage amplitude.

The Receiver is capable of handling only smaller signals Therefore it is desirable to isolate the pulser circuit from the receiver circuit.

Pulse-Echo Instrumentation The Transmit Receive Switch TRS – positioned at the input of the receiver and is designed to pass only voltages signals originating at the transducer by the returning echoes.

Pulse-Echo Instrumentation The Receiver Unit consist of 1. Radiofrequency Amplifier 2. Time gain compensation TGC unit 3. Demodulation Circuit 4. Detector Circuit 5. Video Amplifier

MEMORY PULSER

TRX

TGC UNIT

TRS

RF RECEIVER CRT DISPLAY DEMODULATOR

DETECTOR

VIDEO AMPLIFIER

Pulse-Echo Instrumentation Radio-Frequency Amplifier • Amplify weak voltage signals.

• This is called GAIN

Pulse-Echo Instrumentation Electric signals generated by the transducer are weak and needs amplification.

The gain is the ratio of the output to input Voltage or Power.

Gain = Voltage Out Voltage In

Pulse-Echo Instrumentation The Imaging effect of adjusting gain are: 1. Increasing the gain - increased sensitivity, better penetration 2. Decreasing the gain – decreased sensitivity, less penetration 3. Too high a gain – overloads the display, loss or spatial resolution

Amplitude

Pulse-Echo Instrumentation

Saturation Level

Normal Gain

Distance

Pulse-Echo Instrumentation Excess Gain Amplitude

Saturation Level

Distance

Pulse-Echo Instrumentation Primary objective of grayscale pulse-echo imaging is to make all like reflectors appear the same in the Image regardless where they are located in the sound beam.

Pulse-Echo Instrumentation Time Gain Compensation TGC TGC - electronic process of adjusting the overall system gain as a function of the transmit time.

Pulse-Echo Instrumentation TGC Controls • Near Gain • Slope Delay • Slope • Knee • Far Gain • Body Wall

Pulse-Echo Instrumentation KNEE

Gain dB

NEAR GAIN

DELAY

SLOPE

Depth cm

MAX GAIN

Pulse-Echo Instrumentation KNEE

Gain dB

NEAR GAIN SLOPE

Depth cm Body wall

MAX GAIN

Pulse-Echo Instrumentation KNEE

Gain dB

SLOPE CUT-OFF

DELAY

Depth cm

Pulse-Echo Instrumentation The slide potentiometer allows adjustment of receiver gain for small discrete depth increments.

Pulse-Echo Instrumentation Slide Potentiometer

Gain dB

Depth (Time)

Pulse-Echo Instrumentation Frequency Tuning of the Receiver The frequency band width of the receiver refers to the range of ultrasound signal frequencies that the receiver can amplify with a maximum gain.

Pulse-Echo Instrumentation Types of Amplifiers • Wide-Band • Narrow-Band

Pulse-Echo Instrumentation Wide-band amplifier

Narrow-band amplifier

Gain

Gain

Frequency MHz

Frequency MHz

Pulse-Echo Instrumentation Receiver Unit

Receiver A

Receiver B Output To System

TRX Receiver C

Frequency Selector Switch

Receiver D

Pulse-Echo Instrumentation DYNAMIC RANGE The dynamic range is a measure of the range of echo signal amplitudes.

The dynamic range can be measured at any point.

The dynamic range decreases from transducer, to receiver to scan converter and finally to display.

Pulse-Echo Instrumentation Large range in signal amplitudes is due to: 1. Normal variation in the reflection amplitude.

2. Frequency dependent tissue attenuation.

Pulse-Echo Instrumentation RF amplifier can handle a wide range of signal amplitude at its input – but cannot accommodate the corresponding output using linear amplification.

Pulse-Echo Instrumentation Linear amplification - all voltages amplitudes, regardless of size at the point of input are amplified with the same gain factor.

Pulse-Echo Instrumentation LOGARITHMIC AMPLIFICATION In Logarithmic amplification weak echoes amplitudes are amplified more than strong echoes.

This can reduced the dynamic range by as much as 50%.

The process of reducing the signal DR by electronic means is called COMPRESSION

Pulse-Echo Instrumentation

A

Linear Amplification

Gain

B Logarithmic Amplification

Input signal

Pulse-Echo Instrumentation R-F amplifier can also set the electronic level in the machine.

S-N level – compares real echo signals the system can handle versus the non-echo signals presents (Noise).

The Higher the SN ratio – better the operation of the system.

Pulse-Echo Instrumentation Pre-amplification is a technique to reduce system noise.

Positioning of part of the amplifier circuitry in the transducer housing reduces system noise.

Pulse-Echo Instrumentation REJECTION Rejection is the receiver function that enables the operator to systematically increase or decrease the minimum echo signal amplitude which can be displayed.

Alternate names = Threshold, Suppression.

Pulse-Echo Instrumentation Saturation Level

Rejection Level Dynamic Range Noise Level Zero Signal Level

Pulse-Echo Instrumentation SIGNAL PROCESSING RF waveform – oscillating type of voltage signal (AC) First Step in processing the signal is Demodulation.

Demodulation is the process of converting the electric signal from one form to another.

Pulse-Echo Instrumentation DEMODULATION  Rectification  Detection

Pulse-Echo Instrumentation RECTIFICATION • Rectification results in the elimination of the negative portion of the RF signals •

Half Wave Rectification

•

Full wave Rectification

Pulse-Echo Instrumentation Half-Wave Rectification

Pulse-Echo Instrumentation Full-Wave Rectification

Pulse-Echo Instrumentation DETECTION The main effect of detecting the rectified RF signal is to round out or smooth the signal as to have a single broad peak.

The rectified RF signal following detection is referred to as a Video Signal.

Pulse-Echo Instrumentation Smoothing

Pulse-Echo Instrumentation The video signal is then further amplified by the VIDEO AMPLIFIER. The output from the video amplifier is forwarded to 1. CRT or 2. Scan converter

Pulse-Echo Instrumentation DIGITAL SCAN CONVERTER The device that stores the echo signal is called a Scan converter.

Pulse-Echo Instrumentation All Scan Converters are designed to 1. Store echoes in appropriate location 2. Encode echoes in shade of gray 3. Read out echoes in a horizontal raster format

Pulse-Echo Instrumentation 4. Digital Memory is divided into small squares = Pixel.

5. The Pixels form the Image Matrix 6. Total # of storage location = rows x columns 7. x and y location = ADDRESS

Matrix

Rows x, coordinates

Matrix

Columns, y coordinates

Matrix Pixel

10x 10y

X, Y ADDRESS 8x 7y

5x 5y

3x 3y

1x 1y

Pulse-Echo Instrumentation In the Scan converter the echoes are processed on a firstcome first-in basis.

X X X

X

X X

X X X

X X X

X X X

X

X X

X X X

X X X

50

50

50

50

50

50

50

50 50

50 50

50

Raster Process

50

50

50

50

50

50

50

50 50

50 50

50

Pulse-Echo Instrumentation DIGITAL SCAN CONVERTER • Convert echo voltage signal into a numerical value.

•

Each numerical value corresponds to a shade of gray.

Pulse-Echo Instrumentation The number of shades of gray is determined by the BIT CAPACITY. # of shades of gray = 2

Pulse-Echo Instrumentation Echoes dB

Pulse-Echo Instrumentation Bit

Shades of Gray

1

2

2

4

3

8

4

16

5

32

6

64

7

128

8

256

Pulse-Echo Instrumentation Gray Scale Resolution = dynamic range (dB) # of gray shades

Pulse-Echo Instrumentation Operator can select different A/D conversion scheme (Preprocessing).

Each preprocessing curve is called an algorithm and assigns a specific percentage amount of shades of gray to regions of the echo amplitude.

Pulse-Echo Instrumentation % Available Shade of gray

100% 1 2 50% 3

4

0% Echo Strength

Pulse-Echo Instrumentation POST PROCESSING Assignment of specific display brightness to numerical echo amplitudes read out of the digital memory.

Pulse-Echo Instrumentation 9

7

8

8

8

8

8

8

8

9

8

7

8

8

8

8

7

8

8

9

8

8

8

8

SMOOTHING

Pulse-Echo Instrumentation The DSC is not necessary for image display, but is needed for the following post-processing functions.

• Video Invert • Display Invert • Display Subdivision • Zoom Magnification

Pulse-Echo Instrumentation Zoom Magnification • Read Zoom • Write Zoom

Pulse-Echo Instrumentation Resolution at the DSC 1. Find Matrix size 2. Determine FOV ( width/length) 3. Calculate pixels/cm 4. Find linear distance/pixel = resolution

Pulse-Echo Instrumentation Data PreProcessing

ADC

Echo Signal

Data Collection & Formatting

M A R

Data PostProcessing

Data Reformatting

Positional Data

Display

Pulse-Echo Instrumentation 1. ROM 2. PROM 3. RAM

65. In Figure 3, transducer A is being used to establish: A. B. C. D.

Verification of wedge angle Sensitivity calibration Resolution An index point

66. In Figure 3, transducer C is being used to check: A. B. C. D.

Distance calibration Resolution Sensitivity calibration Verification of wedge angle

67. In Figure 3, transducer D is being used to check: A. B. C. D.

Sensitivity calibration Distance calibration Resolution Verification of wedge angle

68. When the incident angle is chosen to be between the first and second critical angles, the ultrasonic wave generated within the part will be: A. B. C. D.

Longitudinal Shear Surface Lamb

69. In Figure 4, transducer B is being used to check: A. B. C. D.

The verification of wedge angle Resolution Sensitivity calibration Distance calibration

Q: In a UT test system where signal amplitudes are displayed on a CRT, an advantage of a frequency-independent attenuator over a continuously variable gain control is that: A. the pulse shape distortion is less B. the signal amplitude measured using the attenuator is independent of frequency C. the dynamic range of the system is decreased D. the effect of amplification threshold is avoided Q: An amplifier in which received echo pulses must exceed a certain threshold voltage before they can be indicated might be used to: A. suppress amplifier noise, unimportant scatter echoes, or small flaw echoes which are of no consequence B. provide a screen display with nearly ideal vertical linearity characteristics C. compensate for the unavoidable effects of material attenuation loss D. provide distance amplitude correction automatically

Q: The output voltage from a saturated amplifier is: A) 180 degrees out of phase from the input voltage B) lower than the input voltage C) nonlinear with respect to the input voltage D) below saturation Q: The transmitted pulse at the output of the pulser usually has a voltage of 100 to 1000V, whereas the voltages of the echo at the input of the amplifier are on the order of: A) 10 Volts B) 50 Volts C) .001 to 1 Volts D) 1 to 5 Volts

Q: The intended purpose of the adjustable calibrated attenuator of a UT instrument is to: A) control transducer dampening B) increase the dynamic range of the instrument C) broaden the frequency range D) attenuate the voltage applied to the transducer

Addendum-02 Equations & Calculations

My ASNT Level III UT Study Notes 2014-June.

Trigonometry

http://www.mathwarehouse.com/trigonometry/sine-cosine-tangent.php

Contents: 1. Material Acoustic Properties 2. Ultrasonic Formula 3. Properties of Acoustic Wave 4. Speed of Sound 5. Attenuation 6. What id dB 7. Acoustic Impedance 8. Snell’s Law 9. S/N Ratio 10. Near / Far Field 11. Focusing & Focal Length 12. Offsetting for Circular Specimen 13. Quality “Q” Factors 14. Inverse Law & Inverse Square Law

http://www.ndt-ed.org/GeneralResources/Calculator/calculator.htm

1.0

Material Acoustic Properties

Material

Logitudinal wave

Shear wave

mm/μs

mm/μs

Z Acoustic Impedence

Acrylic resin (Perspex)

2.74

1.44

3.23

Steel - SS 300 Series

5.613

3.048

44.6

Steel - SS 400 Series

5.385

2.997

41.3

Steel 1020

5.893

3.251

45.4

Steel 4340

5.842

3.251

45.6

http://www.ndtcalc.com/utvelocity.html

2.0

Ultrasonic Formula

http://www.ndt-ed.org/GeneralResources/Calculator/calculator.htm

Ultrasonic Formula

Ultrasonic Formula

Îą = Transducer radius

3.0

Properties of Acoustic Plane Wave

Wavelength, Frequency and Velocity Among the properties of waves propagating in isotropic solid materials are wavelength, frequency, and velocity. The wavelength is directly proportional to the velocity of the wave and inversely proportional to the frequency of the wave. This relationship is shown by the following equation.

4.0

The Speed of Sound

Hooke's Law, when used along with Newton's Second Law, can explain a few things about the speed of sound. The speed of sound within a material is a function of the properties of the material and is independent of the amplitude of the sound wave. Newton's Second Law says that the force applied to a particle will be balanced by the particle's mass and the acceleration of the the particle. Mathematically, Newton's Second Law is written as F = ma. Hooke's Law then says that this force will be balanced by a force in the opposite direction that is dependent on the amount of displacement and the spring constant (F = -kx). Therefore, since the applied force and the restoring force are equal, ma = -kx can be written. The negative sign indicates that the force is in the opposite direction.

F= ma = -kx

What properties of material affect its speed of sound?

Of course, sound does travel at different speeds in different materials. This is because the (1) mass of the atomic particles and the (2) spring constants are different for different materials. The mass of the particles is related to the density of the material, and the spring constant is related to the elastic constants of a material. The general relationship between the speed of sound in a solid and its density and elastic constants is given by the following equation:

V is the speed of sound Eleatic constant → spring constants

Density → mass of the atomic particles

Where V is the speed of sound, C is the elastic constant, and p is the material density. This equation may take a number of different forms depending on the type of wave (longitudinal or shear) and which of the elastic constants that are used. The typical elastic constants of a materials include:  Young's Modulus, E: a proportionality constant between uniaxial stress and strain.  Poisson's Ratio, n: the ratio of radial strain to axial strain  Bulk modulus, K: a measure of the incompressibility of a body subjected to hydrostatic pressure.  Shear Modulus, G: also called rigidity, a measure of a substance's resistance to shear.  Lame's Constants, l and m: material constants that are derived from Young's Modulus and Poisson's Ratio.

E/N/G

5.0

Attenuation

The amplitude change of a decaying plane wave can be expressed as:

In this expression Ao is the unattenuated amplitude of the propagating wave at some location. The amplitude A is the reduced amplitude after the wave has traveled a distance z from that initial location. The quantity Îą is the attenuation coefficient of the wave traveling in the z-direction. The Îą dimensions of are nepers/length, where a neper is a dimensionless quantity. The term e is the exponential (or Napier's constant) which is equal to approximately 2.71828.

http://www.ndt.net/article/v04n06/gin_ut2/gin_ut2.htm

Spreading/ Scattering/ adsorption (reflection is a form of scaterring) Adsoprtion

Scaterring

Spreading

Scaterrring

Attenuation can be determined by evaluating the multiple backwall reflections seen in a typical A-scan display like the one shown in the image at the bottom.

The number of decibels between two adjacent signals is measured and this value is divided by the time interval between them. This calculation produces a attenuation coefficient in decibels per unit time Ut. This value can be converted to nepers/length by the following equation.

Where v is the velocity of sound in meters per second and Ut is in decibels per second.

Amplitude at distance Z

Where v is the velocity of sound in meters per second and Ut is in decibels per second (attenuation coefficient). Îą is the attenuation coefficient of the wave traveling in the z-direction. The Îą dimensions of are nepers/length (nepers constant).

Attenuation is generally proportional to the square of sound frequency.

Quoted values of attenuation are often given for a single frequency, or an attenuation value averaged over many frequencies may be given. Also, the actual value of the attenuation coefficient for a given material is highly dependent on the way in which the material was manufactured. Thus, quoted values of attenuation only give a rough indication of the attenuation and should not be automatically trusted. Generally, a reliable value of attenuation can only be obtained by determining the attenuation experimentally for the particular material being used.

Attenuation � Frequency2 (f )2

Which Ut?

U0t , A0o U1t , A1o , α1 1

1

7.0

Acoustic Impedance

Sound travels through materials under the influence of sound pressure.

Because molecules or atoms of a solid are bound elastically to one another, the excess pressure results in a wave propagating through the solid.

The acoustic impedance (Z) of a material is defined as the product of its density (p) and acoustic velocity (V).

Z = pV Acoustic impedance is important in: 1. the determination of acoustic transmission and reflection at the boundary of two materials having different acoustic impedances.

2. the design of ultrasonic transducers.

3. assessing absorption of sound in a medium.

The following applet can be used to calculate the acoustic impedance for any material, so long as its density (p) and acoustic velocity (V) are known. The applet also shows how a change in the impedance affects the amount of acoustic energy that is reflected and transmitted. The values of the reflected and transmitted energy are the fractional amounts of the total energy incident on the interface. Note that the fractional amount of transmitted sound energy plus the fractional amount of reflected sound energy equals one. The calculation used to arrive at these values will be discussed on the next page.

http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Physics/applet_2_6/applet_2_6.htm

Reflection/Transmission Energy as a function of Z

Reflection and Transmission Coefficients (Pressure)  This difference in Z is commonly referred to as the impedance mismatch.  The value produced is known as the reflection coefficient. Multiplying the reflection coefficient by 100 yields the amount of energy reflected as a percentage of the original energy.  the transmission coefficient is calculated by simply subtracting the reflection coefficient from one.

Ipedence mismatch

Reflection coefficient

Using the above applet, note that the energy reflected at a water-stainless steel interface is 0.88 or 88%. The amount of energy transmitted into the second material is 0.12 or 12%. The amount of reflection and transmission energy in dB terms are -1.1 dB and -18.2 dB respectively. The negative sign indicates that individually, the amount of reflected and transmitted energy is smaller than the incident energy.

If reflection and transmission at interfaces is followed through the component, only a small percentage of the original energy makes it back to the transducer, even when loss by attenuation is ignored. For example, consider an immersion inspection of a steel block. The sound energy leaves the transducer, travels through the water, encounters the front surface of the steel, encounters the back surface of the steel and reflects back through the front surface on its way back to the transducer. At the water steel interface (front surface), 12% of the energy is transmitted. At the back surface, 88% of the 12% that made it through the front surface is reflected. This is 10.6% of the intensity of the initial incident wave. As the wave exits the part back through the front surface, only 12% of 10.6 or 1.3% of the original energy is transmitted back to the transducer.

Practice Makes Perfect Following are the data:

Q1: What is the percentage of initial incident sound wave that will reflected from the water/Aluminum interface when the sound first enter Aluminum?

R= (Z1-Z2)2 / (Z1+Z2)2 = (0.149-1.72)2/(0.149+1.72)2 R= 0.707, Answer= 70.7%

Q2: What is the percentage of sound energy that will finally reenter the water after reflected from the backwall of Aluminum? (Do not consider material attenuation and other factors) Answer: 6%

0.706 – initial Back wall

0.2934

0.207x 0.2934=0.0609 Second Backwall echo 0.2934x 0.706 = 0.207

8.0

Snell’s Law

Snell's Law holds true for shear waves as well as longitudinal waves and can be written as follows

= Where: VL1 is the longitudinal wave velocity in material 1.

VL2 is the longitudinal wave velocity in material 2.

VS1 is the shear wave velocity in material 1.

VS2 is the shear wave velocity in material 2.

Snell’s Law

http://education-portal.com/academy/lesson/refraction-dispersion-definition-snells-law-index-of-refraction.html#lesson

Practice Makes Perfect 5. For an ultrasonic beam with normal incidence, the reflection coefficient is given by: (a) [(Z1+Z2)2]/[(Z1-Z2)2] (b) (Z1+Z2)/(Z1-Z2) (c) [(4) (Z1)(Z2)]/[(Z1+Z2)2] (d) [(Z1-Z2)2]/[Z1+Z2)2] 6. For an ultrasonic beam with normal incidence the transmission coefficient is given by: (a) [(Z1+Z2)2]/[(Z1-Z2)2] (b) (Z1+Z2)/(Z1-Z2) (c) [(4) (Z1)(Z2)]/[(Z1+Z2)2] (d) [(Z1-Z2)2]/[Z1+Z2)2]

Practice Made Perfect 7. Snell's law is given by which of the following: (a) (Sin A)/(Sin B) = VB/VA (b) (Sin A)/(Sin B) = VA/VB (c) (Sin A)/ VB = V(Sin B)/VA (d) (Sin A)[VA] = (Sin B)[ VB] 8. Snell's law is used to calculate: (a) Angle of beam divergence (b) Angle of diffraction (c) Angle of refraction (d) None of the above

Practice Makes Perfect 9. Calculate the refracted shear wave angle in steel [VS = 0.323cm/microsec] for an incident longitudinal wave of 37.9 degrees in Plexiglas [VL = 0.267cm/ microsec] (a) 26 degrees (b) 45 degrees (c) 48 degrees (d) 64 degrees 10. Calculate the refracted shear wave angle in steel [VS = 0.323cm/microsec] for an incident longitudinal wave of 45.7 degrees in Plexiglas [VL = 0.267cm/ microsec] (a) 64 degrees (b) 45.7 degrees (c) 60 degrees (d) 70 degrees

Practice Makes Perfect 11. Calculate the refracted shear wave angle in aluminium [VS = 0.31cm/ microsec] for an incident longitudinal wave of 43.5 degrees in Plexiglas [VL = 0.267cm/microsec] (a) 53 degrees (b) 61 degrees (c) 42 degrees (d) 68 degrees 12. Calculate the refracted shear wave angle in aluminium [VS = 0.31cm/microsec] for an incident longitudinal wave of 53 degrees in Plexiglas [VL = 0.267cm/microsec] (a) 53 degrees (b) 61 degrees (c) 42 degrees (d) 68 degrees

9.0

S/N Ratio

The following formula relates some of the variables affecting the signal-tonoise ratio (S/N) of a defect:

FOM: Factor of merits at center frequency

The following formula relates some of the variables affecting the signal-tonoise ratio (S/N) of a defect:

Sound Volume: Area x pulse length Δt

Material properties Flaw geometry at center frequency: Figure of merit FOM and amplitudes responds

10.

Near/ Far Fields

http://miac.unibas.ch/PMI/05-UltrasoundImaging.html

where Îą is the radius of the transducer and Îť the wavelength.

For beam edges at null condition K=1.22

Modified Near Zone

T Perspex

Modified Zf

Example: Calculate the modified Near Zone for; • 5 MHz shear wave transducer • 10mm crystal • 10 mm perspex wedge Perspex L-wave: 2730 m/s Steel S-wave: 3250 m/s Steel L-wave: 5900 m/s Modified NZ= (0.012 x f) / (4v) – 0.01(2730/3250) =0.0300m = 30mm

Apparent Near Zone distance

11.0

Focusing & Focal Length

http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/beam-characteristics/

The focal length F is determined by following equation;

Where: F = Focal Length in water R = Curvature of the focusing len n = Ration of L-velocity of epoxy to L-velocity of water

12.0

Offset of Normal probe above circular object V1

θ1

θ1

R

θ2 V2

Calculate the offset for following conditions: Aluminum rod being examined is 6" diameter, what is the off set needed for (a) 45 refracted shear wave (b) Longitudinal wave to be generated?

(L-wave velocity for AL=6.3x105cm/s, T-wave velocity for AL=3.1x105 cm/s, Wave velocity in water=1.5X105 cm/s) Question (a)

Question (b)

13.0

“Q” Factor

3dB down

14.0

Inverse Law and Inverse Square Law

For a small reflector where the size of reflector is smaller than the beam width, the echoes intensity from the same reflector varies inversely to the square of the distance.

5cm

75% FSH

7.5cm

33% FSH

Inverse Square Law

http://www.cyberphysics.co.uk/general_pages/inverse_square/inverse_square.htm

Inverse Law: For large reflector, reflector greater than the beam width, e.g. backwall echoes from the same reflector at different depth; the reflected signal amplitude varies inversely with the distance.

10cm

7.5cm

DGS Distance Gain Sizing

Y-axis shows the Gain

size of reflector is given as a ratio between the size of the disc and the size of the crystal.

X-axis shows the Distance from the probe in # of Near Field

DGS Distance Gain Sizing

Y-axis shows the Gain

size of reflector is given as a ratio between the size of the disc and the size of the crystal.

X-axis shows the Distance from the probe in # of Near Field

– Distance Gain Size is a method of setting sensitivity or assessing the signal from an unknown reflector based on the theoretical response of a flatbottomed hole reflector perpendicular to the beam axis. (DGS does not size the flaw, but relate it with a equivalent reflector) The DGS system was introduced by Krautkramer in 1958 and is referred to in German as AVG. A schematic of a general DGS diagram is shown in the Figure. The Y-axis shows the Gain and X-axis shows the Distance from the probe. In a general DGS diagram the distance is shown in units of Near Field and the scale is logarithmic to cover a wide range.

The blue curves plotted show how the amplitudes obtained from different sizes of disc shaped reflector (equivalent to a FBH) decrease as the distance between the probe and the reflector increases.

In the general diagram the size of reflector is given as a ratio between the size of the disc and the size of the crystal. The red curve shows the response of a backwall reflection. The ratio of the backwall to the crystal is infinity (∞).

Specific DGS curves for individual probes can be produced and so both the distance axis and the reflector sizes can be in mm.

If the sensitivity for an inspection is specified to be a disc reflector of a given size, the sensitivity can be set by putting the reflection from the backwall of a calibration block or component to the stated %FSH. The gain to be added can be then obtained by the difference on the Y-axis between the backwall curve at the backwall range and the curve of the disc reflector of the given size at the test range. If the ranges of the backwall and the disc reflector are different, then attenuation shall be accounted for separately. Alternatively, the curves can be used to find the size of the disc shaped reflector which would give the same size echo as a response seen in the flaw detector screen.

20-4dB=16dB (deduced) Δ Flaw =30-16=14dB

Data: Probe frequency: 5MHz Diameter: 10mm compression probe Plate thickness: 100mm steel Defect depth: 60mm deep Gain for flaw to FSH: 30dB BWE at 100mm: 20dB

20dB (measured)

Example: If you has a signal at a certain depth, you can compare the signal of the flaw to what the back wall echo (BWE) from the same depth and estimate the FBH that would give such a signal at the same depth. The defect can then be size according to a FBH equivalent.

Data: Probe frequency: 5MHz Diameter: 10mm compression probe Plate thickness: 100mm steel Defect depth: 60mm deep Gain for flaw to FSH: 30dB BWE at 100mm: 20dB ------------------------------------------------------------------------Near field: 21mm, flaw location= 3xNear Field From the chart BWE at 60mm will be 20-4dB=16dB Flaw signal Gain is 30dB-16dB= 14dB Used the flaw signal Gain and locate the equivalent reflector size is between 0.4 to 0.48 of the probe diameter, say 0.44 x10mm = 4.4mm equivalent reflector size.

http://www.olympus-ims.com/en/atlas/dgs/

More on DGS/AVG by Olympus http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/dgs-avg/

DGS is a sizing technique that relates the amplitude of the echo from a reflector to that of a flat bottom hole at the same depth or distance. This is known as Equivalent Reflector Size or ERS. DGS is an acronym for DistanceGain-Size and is also known as AVG from its German name, Abstand Verstarkung Grosse. Traditionally this technique involved manually comparing echo amplitudes with printed curves, however contemporary digital flaw detectors can draw the curves following a calibration routine and automatically calculate the ERS of a gated peak. The generated curves are derived from the calculated beam spreading pattern of a given transducer, based on its frequency and element diameter using a single calibration point.

Material attenuation and coupling variation in the calibration block and test specimen can be accounted for.

DGS is a primarily mathematical technique originally based on the ratio of a circular probe’s calculated beam profile and measurable material properties to circular disk reflectors. The technique has since been further applied to square element and even dual element probes, although for the latter, curve sets are empirically derived. It is always up to the user to determine how the resultant DGS calculations relate to actual flaws in real test pieces.

An example of a typical DGS curve set is seen below. The uppermost curve represents the relative amplitude of the echo from a flat plate reflector in decibels, plotted at various distances from the transducer, and the curves below represent the relative amplitude of echoes from progressively smaller disk reflectors over the same distance scale.

As implemented in contemporary digital flaw detectors, DGS curves are typically plotted based on a reference calibration off a known target such as a backwall reflector or a flat bottom hole at a given depth. From that one calibration point, an entire curve set can be drawn based on probe and material characteristics. Rather than plotting the entire curve set, instruments will typically display one curve based on a selected reflector size (registration level) that can be adjusted by the user.

In the example below, the upper curve represents the DGS plot for a 2 mm disk reflector at depths from 10 mm to 50 mm. The lower curve is a reference that has been plotted 6 dB lower. In the screen at left (figure 1), the red gate marks the reflection from a 2 mm diameter flat bottom hole at approximately 20 mm depth. Since this reflector equals the selected registration level, the peak matches the curve at that depth. In the screen at right (Figure 2), a different reflector at a depth of approximately 26 mm has been gated. Based on its height and depth in relation to the curve the instrument calculated an ERS of 1.5 mm.

Figure1:

Figure2:

DGS Distance Gain Sizing

Y-axis shows the Gain

size of reflector is given as a ratio between the size of the disc and the size of the crystal.

X-axis shows the Distance from the probe in # of Near Field

– Distance Gain Size is a method of setting sensitivity or assessing the signal from an unknown reflector based on the theoretical response of a flatbottomed hole reflector perpendicular to the beam axis. (DGS does not size the flaw, but relate it with a equivalent reflector) The DGS system was introduced by Krautkramer in 1958 and is referred to in German as AVG. A schematic of a general DGS diagram is shown in the Figure. The Y-axis shows the Gain and X-axis shows the Distance from the probe. In a general DGS diagram the distance is shown in units of Near Field and the scale is logarithmic to cover a wide range.

The blue curves plotted show how the amplitudes obtained from different sizes of disc shaped reflector (equivalent to a FBH) decrease as the distance between the probe and the reflector increases.

In the general diagram the size of reflector is given as a ratio between the size of the disc and the size of the crystal. The red curve shows the response of a backwall reflection. The ratio of the backwall to the crystal is infinity (∞).

Specific DGS curves for individual probes can be produced and so both the distance axis and the reflector sizes can be in mm.

If the sensitivity for an inspection is specified to be a disc reflector of a given size, the sensitivity can be set by putting the reflection from the backwall of a calibration block or component to the stated %FSH. The gain to be added can be then obtained by the difference on the Y-axis between the backwall curve at the backwall range and the curve of the disc reflector of the given size at the test range. If the ranges of the backwall and the disc reflector are different, then attenuation shall be accounted for separately. Alternatively, the curves can be used to find the size of the disc shaped reflector which would give the same size echo as a response seen in the flaw detector screen.

15.0

Pulse Repetitive Frequency/Rate and Maximum Testable Thickness

Clock interval = 1/PRR Maximum testable length = ½ x Velocity x Clock interval Note: The Clock interval has neglected the time occupied by each pulse.

16.0

Immersion Testing of Circular Rod

Q4-12 Answer: First calculate the principle offset d; ϴ = Sin-1(1483/3250 xSin45)=18.8 ° d=R.Sin18.8= 0.323 (Assume R=1).

Wobbling ±10%; d’=0.355 ~ 0.290 d’=0.355, ϴ = Sin-1(0.355)=20.8 ° giving inspection Φ = Sin-1(3250/1483xSin20.8)=51, 13.3% above 45 ° d’=0.290, ϴ = Sin-1(0.290)=16.9 ° giving inspection Φ = Sin-1(3250/1483xSin16.9)=39.6, 12% below 45 °

Maximum ϴ

ϴ max = Sin-1 (ID/OD)

Addendum-03 Questions & Answers Collection of My Pitfalls

Uncertain Questions 21. Which type of calibration block is used to determine the resolution of angle beam transducers per requirements of AWS and AASHTO a. b. c. d.

An IIW block A DSC block A rompus block An RC block

24. Resonance or standing waves are a result of: a. b. c. d.

mode conversion interference from reflected waves beam divergence (spread) attenuation of the sound waves

Make mistakes now, not during exam!

RC- Resolution Calibration Block

30. On an A-scan display the dead zone refers to: a. the distance contained within the near field (incorrect) b. the area outside the beam spread c. the distance covered by the front surface pulse width and recovery time d. the area between the near field and the far field 40. The second critical angle is the angle of the incident beam at which: a. b. c. d.

the angle of the refracted compression wave is 900 the angle of the reflected compression wave is 90° total reflection occurs surface waves are produced

--------------------------------------------------------------------------------

17. Surface waves are used to detect discontinuities in the test materials: a. b. c. d.

At half the depth.

Above the lower surface.

On the surface where the probe is in contact.

None of the above.

26. Which of the following probes is most commonly used for testing welded metals for laminations before angle beam inspection. a. b. c. d.

Surface wave probe.

Twin crystal 0° probe.

Single crystal probe.

An angle probe.

29. Artificial flaws can be produced by using: Side drilled holes Flat bottom holes EDM notches (http://www.phtool.com/pages/edm.asp) All of the above

31. As the acoustic impedance ratio between two materials approaches 1 the amount of sound reflected at an interface: a. b. c. d.

increases. decreases. is not affected. varies depending upon the velocity of the materials.

34. Significant errors in ultrasonic thickness measurements can occur if; a. Test frequency is varying at a constant rate. b. The velocity of propagation deviates substantially from an assumed constant value for a given material. c. Water is employed as a couplant between the transducer and the part being measured. d. None of the above should cause errors.

45. When examining thin materials for planar discontinuities oriented parallel to the part surface, what testing method is most often used: a. b. c. d.

Angle beam Through-transmission Straight beam - single crystal Straight beam - dual crystal

7. The ultrasonic test method in which finger damping in most effective in locating a discontinuity is: a. b. c. d.

shear wave longitudinal wave surface wave compressional wave

15. Which type of test block is used to check horizontal linearity and the dB accuracy per requirements of AWS and AASHTO? a. b. c. d.

Distance/Sensitivity block A DSC block A rompus block A shear wave calibration block

Mistake Made -------------------------------------------------------------------------------Question: Which probe will be used for critical examination in a forged component with a curved surface.: Your answer: 1 megahertz, 10mm dia.

Correct answer: 10 megahertz, 25mm dia.

Question: A general term applied to all cracks, inclusions, blow holes etc, which cause a reflection of sonic energy is: Your answer: a refractor Correct answer: a discontinuity Question: On an A-scan display the dead zone refers to: Your answer: the distance contained within the near field Correct answer: the distance covered by the front surface pulse width and recovery time

Mistake Made -------------------------------------------------------------------------------Question: Dead zone size depends on: Your answer: construction of the probe.

Correct answer: All of the above.

Question: The second critical angle is the angle of the incident beam at which: Your answer: total reflection occurs Correct answer: surface waves are produced ---------------------------------------------------------------------------------

Mistake Made -------------------------------------------------------------------------------Question: When a longitudinal wave encounters an interface between two material with different accoustic impedances, what occurs when the Your answer: Reflection and refraction Correct answer: Reflection Question: In an ultrasonic instrument, the number of pulses produced by an instrument in a given period of time in known as the:Your answer: pulse length of the instrument Correct answer: pulse repetition rate Question: Which probe will be used for critical examination in a forged component with a curved surface.:Your answer: 10 megahertz, 10mm dia.Correct answer: 10 megahertz, 25mm dia.

Question: Which type of screen presentation displays a profile or crosssectional view of the test specimen? Your answer: A-scan Correct answer: B-scan Question: When a longitudinal wave encounters an interface between two material with different accoustic impedances, what occurs when the Your answer: Refraction Correct answer: Reflection

Questions & Answers

Table 1.2

Chapter 1: Physical Principles Q1-10 The acoustic energy reflected at a plexiglass-quartz interface is equal to?

Answer: R= (Z1-Z2)2 / (Z1+Z2)2 = (3.2-15.2)2 / (3.2+15.2)2= 42.53% Q1-11 The acoustic energy transmitted through a plexiglass-water interface is equal to?

Answer: R= (Z1-Z2)2 / (Z1+Z2)2 = (3.2-1.5)2 / (3.2+1.5)2 = 13%, T= 1-R = 87% Q1-12 The first critical angle at a water-plexiglass interface will be?

Answer: ϴ = Sin-1 (1483/2730) = 32.9°

Q1-13 The second critical angle at water-plexiglass interface will be?

Answer: ϴ = Sin-1 (1483/1430) = Error!

Q1-14 The incident angle need in immersion testing to develop a 70 shear wave in plexiglass is equal to?

Answer: ϴ = Sin-1 (1483/1430 x sin70) = 77°

Q1-20 Two plate yield different back-wall reflections in pulse-echo testing (18dB) with their only apparent difference being in the second material void content. The plate are both 3” thick. What is the effective change in acoustic attenuation between the first and second plate?

Answer: Sound path – 2 x thickness = 6” Attenuation = 18dB/6” = 3dB/in.

Comment: The answer could be confused if the pulse-echo testing, 2-ways path length was not considered, arriving with the incorrect answer of 6dB/in

For evaluating material properties always remember to divide the result with the actual sweep distance if necessary! It was not a one-way–trip!

Q1-15 At a water-Aluminum interface, at an incident angle of 20°, the reflected and transmitted wave are?

Answer: 60% transmitted and 40% reflected.

Q1-22 The beam spread half angle I the far field of a I” diameter transducer sending 5MHz longitudinal wave into Plexiglas block is?

Answer: ϴ = Sin-1 (K λ/D) Assumed K=1.2 for null beam edge, ϴ = Sin-1 (K λ/D) =Sin-1(1.2V/DF)= Sin-1[1.2x2730x103/ (25.4x5x106)] =1.478° Q1-23 The near field of a round 1/2 “ diameter contact L-wave transducer being used on a steel test part operating at 3MHz is?

Answer: Z= D2/4λ = 12.72 3x106 x / (4x5900x103) = 20.5mm

Chapter 2: Equipment Q2-5 A 5MHz 0.5” diameter flat search unit in water has a near field length of approximately?

Answer: Z= D2/4λ = (12.72 x 5x106) / (4x 1480X103) = 136mm = 5.36” Q2-7 A 10MHz,0.5” diameter transducer placed on steel and acrylic in succession, the beam spread in these 2 material is? ϴ = sin-1(K λ/D). ϴFe = sin-1(1.2x5920x103/10x106x12.7) = 3.2°, ϴAcrylic = sin-1(1.2x2730x103/10x106x12.7) = 1.48°

Q2-12 An angle beam produce a 45° shear wave in steel, what is the incident angle? (Vs for steel=0.125in/ms, VL for plastid=0.105in/ms) Answer: Snell’s Law; ϴincident = Sin-1[(0.105/0.125) xSin45] = 36.43° Q2-13 Aluminum rod 6” diameter being examined in immersion technique, what is the required offset to generate a 45° refracted shear wave?

Answer: First find the incident angle using Snell’s Law ϴincident = Sin-1[(1.5/3.1) xSin45] = 20° Offset = rSin20 = 3Sin20 = 1.026”

Q2-14 What is the offset required, if 45 refracted longitudinal wave to be generated?

Answer: First find the incident angle using Snell’s Law ϴ incident = Sin-1[(1.5/6.3) xSin45] = 9.69° Offset = r.Sin9.69 ° = 3.Sin9.69 ° = 0.505” Q2-16 In a longitudinal wave immersion test of Titanium plate, an echoes pulse from an internal defect is observed 6.56μs following front echo. How deep is the defect below the front surface?

Answer: Sound path travel= 6100000 x 6.56 x 10-6 = 40mm The actual depth = sound path / 2 = 20mm

Q2-17 A change in echo amplitude from 20% of FSH to 40% of FSH is a change of how many dB? Answer: ΔdB= 20log(20/40) = 6dB drop or -6dB. Q2-20 What is the lens radius of curvature is needed in order to have a 20mm diameter 5MHz transducer focus in water at a distance of 40mm drom the lens face?

Answer: R=F(n-1/n), n= V Lens/V water , n= 2.67/1.49= 1.792.

R=40(0.792/1.792) = 17.7mm

Q2-18 In Fig.29 what is the rate of attenuation in dB/in of 5MHz transducer in Far Field, the horizontal scale is 0.5” per division and the vertical scale is linear.

Answer: ΔI = 20log(1.25/2) D=<2” , Attenuation = 2.04dB/in or ΔI = 20log(1.25/2) D=1.85” , Attenuation = 2.21dB/in or ΔI = 20log(1.075/2.2) D=3” , Attenuation = 2.07dB/in

Q2-19 What is the rate of attenuation for 2.25MHz transducer?

Answer: Δ I = 20log(0.9/2.2) D=2.5” , Attenuation = 3.11dB/in

Q2-21 Two signals were compared to each other. The second was found to be 14dB less than the first. This change could be represented by a change of?

Answer: Î&#x201D;I = 20Log(I/Io), -14dB= 20Log(I/Io), (I/Io)= 0.2 2 answers could be confused: 70% FSH to 14% FSH, a drop of 80% 20% FSH to 100% FSH, an increase of 80%

Q2-11 A change in 16dB on the attenuator correspond to an amplitude ration of: Answer: Î&#x201D;I = 20Log(I/Io), 16dB= 20Log(I/Io), (I/Io)= 6.3

Charter 3: Common Practices Q3-6 In Fig. 3.7 the respond from 3.23mm FBH at a depth of 25mm is above that detected from 1mm FBH by?

Answer: Î&#x201D;dB= 20Log(2.1/0.6) = 10.88

Q3-7 The half angle beam spread of the reflected wave front from #8 FBH in an aluminum “A” block being immersion tested using 25MHz transducer is?

Answer: Focal size = 8/64 x 25.4 =3.175mm diameter.

The beam spread is in aluminum block, the wave velocity VL=6300 m/s The half angle beam spread ϴ= Sin-1(Kλ/D) ϴ = Sin-1[(1.2x6300x103)/(3.175x 25 x 106)] = 5.47° Comment: Be careful with the unit used, my mistake is: ϴ = Sin-1[(1.2x6300x103)/(3.175x 10-3 x 25 x 106)]

Always Check the units correctly!!!! Only Donkey made such mistake!

Monkey made mistake too!

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Q3-8 Answer: The next SDH used will be 5/4T, first SDH after backwall echo.

The node is 5/(4x2) = 5/8 node

Q3-11 When using a focued, straight beam search unit for lamination scanning in an immersion test of steel plate, a change in water path of 0.2” will result in the focal point moving in the steel a distance of?

Answer: The change in water path=0.2” correspond to 0.2 x 1483/5900 = 0.05” Q3-12 A search unit with a foal length in water of 4” is used. A steel plate 8” thick velocity 0.230”/ms is place at a water depth of 2” from the search unit, At what depth is the focal point in steel?

Answer: Focal depth in steel = 2 x Vwater/ Vsteel = 2x1480/5900 = 0.5”

Q3-13 During examination, an indication of 25% FSH is detected and maximized. Foe better analysis the gain is increase by 12bB and the indication increase to 88% FSH. What value should be reached and what is the apparent problem?

Answer: 12dB= 20Log(I/25), I/25= 3.98, I=100%

Q3-23 A air filled #3 FBH 0.5” into the bottom of 4.5” aluminum block, will return to the 0.75” diameter sending immersion transducer ans echo signal equal to ? Of the initial pulse. Assume no attenuation to beam divergence or other causes.

Answer: The size of reflector = 3/64” = 0.046875”.

For a small reflector used inverse square law; Echo1/Echo2 = Area 2 / Area 1 100/x= 0.0468752 / 0.752 , x = 0.39%

Q3-15 In contact testing, the back surface signal from a 2” plate was set at full screen height. Passing over a coarse grained area, the back surface signal dropped to 10% FSH. What is the change in attenuation in this area?

Answer: ΔI=20Log(10/100), the drop in dB= 20dB. The sweep distance = 4” The attenuation is 20/4 = 5dB/in.

Comment: Remember that the attenuation is cause by the sound path traversing thru the sweep distance.

Q4-12 Answer: First calculate the principle offset d; ϴ = Sin-1(1483/3250 xSin45)=18.8 ° d=R.Sin18.8= 0.323 (Assume R=1).

Wobbling ±10%; d’=0.355 ~ 0.290 d’=0.355, ϴ = Sin-1(0.355)=20.8 ° giving inspection Φ = Sin-1(3250/1483xSin20.8)=51, 13.3% above 45 ° d’=0.290, ϴ = Sin-1(0.290)=16.9 ° giving inspection Φ = Sin-1(3250/1483xSin16.9)=39.6, 12% below 45 °

Q4-13 Answer: PRR = number of pulse per second N/s, Length generated by pulse per second = PRR x D For effective inspection Vp â&#x2030;¤ PRR x D Q4-14 Answer: Effective inspection Length generated by the PRR x Width = 600in/s For a defect to be detected 3 time consecutively, the travel speed Vp= 600/3 = 200in/s

Q4-15 Answer: Offset = T.tan70 x Number of ½ skip.

Offset = 3x 1.5 tan70 Comment: 1 skip= 2 legs Q4-16 Answer: ?

Q4-16

Q4-17 Answer: Total length of axial= 8x12x0.0254m L=2.438m, Sweep distance for a complete return loop =2 x L= 4.876m For PRR = 2000 Distance travel by each pulse Lp= 5920/2000 m Lp=2.96m Since Lp is less than the 4.876, the next pulse was found to be generated before the previous echo has returned to the receiver, thus reduce the PRR is required.

Set PRR=1000, yield Lp=5.92m > L=4.876m Will resolve the problem.

Q4-17 Illustrations

Complete loop=4.876m

Length of axial 8â&#x20AC;&#x2122; or 2.438m

The previous pulse return position when 2nd (next) pulse start to send

Incoming & returning wave meet

2nd pulse generating

0.958m

0.958m 0.522m

â&#x201A;ľ

Q4-18 Answer:

8. When testing a 30 mm diameter, 500 mm long shaft from the flat end of the shaft using longitudinal waves from a 20 mm diameter 2 MHz probe, numerous signals are seen on the screen after 500 mm. These are: a) ghost images b) side wall echoes c) internal thread indications d) none of the above

Break!

mms://a588.l3944020587.c39440.g.lm.akamaistream. net/D/588/39440/v0001/reflector:20587?BBCUID=e5203c9d59fef1a79c12d8c601e839f58db16f7d5 d6448f55674c540f1856834&amp;SSO2-UID=

Q5-20 Answer: None of above

Q5-22 Answer: Class C

Q5-22 Table B-1

5. At a solid to free boundary, an obliquely incident longitudinal wave from the solid can result in, at most: a) a reflected longitudinal wave only b) a reflected longitudinal and reflected shear wave c) a refracted longitudinal long wave d) a reflected longitudinal and reflected shear and refracted longitudinal wave 6. Geometric-optic treatment (?) of ultrasonic waves fails to account for: a) reflection b) refraction c) diffraction d) normal incidence 34.The most useful range of incident longitudinal wave angles for ultrasonic testing is: (a) Normal incidence to the first critical angle (b) First critical angle to the second critical angle (?) (c) Second critical angle to the third critical angle (d) Above the third critical angle

38. The angle of a refracted shear wave generated as a sound wave passes at an angle through an acoustic interface is dependant on: a) The acoustic impedances of the materials of each side of the interface b) The frequency of the incident sound wave c) The wavelength of the incident sound wave d) The hardness of the materials on each side of the interface 22. The three most common modes of sound vibration are: (a) Longitudinal, compressional, and transverse waves (b) Longitudinal, transverse and rayleigh waves (c) Transverse, longitudinal and shear waves (d) Transverse, shear waves and rayleigh waves

13. An oscilloscope display in which the screen base line is adjusted to represent the one way distance in a test piece is called a: (a) A scan display (b) B scan display (c) C scan display (d) D scan display 12. Which of the following test frequencies would generally provide the best penetration in a 12 inch thick specimen of coarse-grained steel? (a) 1.0 MHz (b) 2.25 MHz (c) 5.0 MHz (d) 10 MHz (Incorrect â&#x20AC;&#x201C; silly mistake)

48. A more highly damped transducer crystal results in: (a) Better resolution (b) Better sensitivity (mistake) (c) Lower sensitivity (d) Poorer resolution 6. The portion of a test piece which is represented by the CRT screen area from zero to the rightmost edge of the initial pulse is called: (a) The dead zone (mistake) (b) The near field (c) The near zone (d) The far zone

17. Transducer focal lengths are normally specified as: (a) Distance in steel (b) Distance in aluminium (c) Distance in air (d) Distance in water (mistake) 21. An advantage of using a ceramic transducer in search units is that: (a) It is one of the most efficient generators of ultrasonic energy (b) It is one of the most efficient receivers of ultrasonic energy (c) It has a very low mechanical impedance (d) It can withstand temperatures as high as 700oC

47. When a vertical indication has reached the maximum signal height which can be displayed or viewed on the CRT of an ultrasonic instrument, the indication is said to have reached its: (a) Distance-amplitude height (mistake) (b) Absorption level (c) Vertical level (d) Limit of resolution

53. An ultrasonic instrument control which is used to adjust the sharpness of the CRT screen display is called: (a) Astigmatism or focus (b) Pulse repetition rate (c) Pulse energy (d) Gain

63. The purpose of the couplant is to: (a) Match impedances between the transducer and test piece (b) Absorb stray reflectors (c) Clean the test piece so a more efficient test may be continued (d) Lock the ultrasonic scanner into place prior to testing Note: by exclude the air between the 2 interfaces.

72. When conducting an immersion test, the water path distance must be controlled so that: a) Spurious signals are not created by surface waves on the test piece b) The (water path distance)/(diameter) ratio does not result in asymmetric standing waves c) The test piece discontinuity indications appear between the first front and first back surface echoes d) The second front surface echo does not appear on the CRT screen between the first front and first back surface echoes (?)

Immersion Testing Method

Standards Answer: C

Standards Answer: B

Standards Answer: A

Standards Answer: A (or C?)

Standards Answer: A

Standards Answer: C

Standards Answer: B

Standards Answer: C

Standards Answer: C

Standards Answer: A?

Arrows shown standard correct answers: Level I Q&A

Arrows shown standard correct answers: Level I Q&A

Study Blueeeeeeeeâ&#x20AC;¦ 28th July 2014 17:34

Arrows shown standard correct answers:

mms://a588.l3944020587.c39440.g.lm.akamaistre am.net/D/588/39440/v0001/reflector:20587?BBCUID=e5203c9d59fef1a79c12d8c601e839f58db16f7 d5d6448f55674c540f1856834&amp;SSO2-UID=

Arrows shown standard correct answers: Level II Q&A

http://www.mtv123.com/mp3/45297/326534.shtml

Arrows shown standard correct answers:

Arrows shown standard correct answers:

R↑∝ F↑

Arrows shown standard correct answers:

Arrows shown standard correct answers:

Arrows shown standard correct answers:

3-Screen Height Linearity The ultrasonic testing instrument shall provide linear vertical presentation within Âą5% (According to ASME Sec.V, Article 5 T-532) of the full screen height for 20% to 80% of the calibrated screen height.

The procedure for evaluating screen height linearity is provided in appendix 1 of article 5, ASME code Sec.V and shall be performed at the beginning of each period of extended use (or every 3 months, which ever is less). http://www.inspection-for-industry.com/ultrasonic-testing.html

Take a break

mms://a588.l3944020587.c39440.g.lm.akamaistream.net/D/588/394 40/v0001/reflector:20587?BBCUID=e5203c9d59fef1a79c12d8c601e839f58db16f7d5d6448f55674c5 40f1856834&amp;SSO2-UID=

Calculation: Incident angle= 7° Refracted longitudinal wave = 29.11° Refracted shear wave = 15.49°

Arrows shown standard correct answers:

Arrows shown standard correct answers: Q2. During ultrasonic inspection of a weld, having a thickness of 28 mm angle beam search units are to be used. The recommended angle of search unit Is: a. 70ยบ b. 60ยบ c. 45ยบ d. any one

Addendum-04 Questions & Answers on Calculations

My ASNT Level III UT Study Notes 2014-June.

Expert at Works

Content: Exercise 1 Exercise 2

Expert at Works too!

Content: Exercise 1 Exercise 2

Expert at Works â&#x20AC;&#x201C; The real achiever!

Questions & Answers

Practices Make Perfect

Practices Make Perfect

Click to Q&A

http://www.ndtcalc.com/index.php?page=quiz&method=ut&qs=50

More Reading Q&A Questions &on Answers

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2.0: Ultrasound Formula

http://www.ndt-ed.org/GeneralResources/Calculator/calculator.htm

Ultrasonic Formula

Ultrasonic Formula

Inverse Law and Inverse Square Law For a small reflector where the size of reflector is smaller than the beam width, the echoes intensity from the same reflector varies inversely to the square of the distance.

5cm

75% FSH

7.5cm

33% FSH

Inverse Square Law

http://www.cyberphysics.co.uk/general_pages/inverse_square/inverse_square.htm

Inverse Law: For large reflector, reflector greater than the beam width, e.g. backwall echoes from the same reflector at different depth; the reflected signal amplitude varies inversely with the distance.

10cm

7.5cm

Echo Amplitude- Reflector Size “D” & Depth “d” Relations: (small reflector- Inverse square law)

Amplitude α D2 Amplitude α 1/d2 Amplitude = kD2/d2 , k =constant Amplitude1/ Amplitude2 = D12 d22 / d12 D22

d

Amplitude D

Echo Amplitude- Reflector Size “D” & Depth “d” Relations: (large reflector- inverse law)

Amplitude α 1/d Amplitude = k/d , k =constant, Amplitude1/ Amplitude2 = d2 / d1

d

Amplitude D

Scanning Speed: Scanner speed = (PRR / Number of hits) × Effective diameter of probe Speed of test part = (PRR / Number of hits) × Effective diameter of probe Where: Effective dia. of probe = Dia. of probe – 2 [ (Dia. of probe) × (Percent of overlap between scan / 100) ] PRR = Pulse Repetition Rate Linear speed of disc or pipe in mm/ s = (2πr x RPM / 60) where r = radius of disc or pipe in mm RPM = Number of Rotation of pipe Per Minute = Revolution Per Minute