Electromagnetic testing q&a 004 part 2 of 2

Electromagnetic Testing Questions & Answers -004 Part 2

ACFM,EC&MFL,RF Testing-Book(E) 2009 My ASNT Level III Pre-Exam Preparatory My Self Study Notes 5th August 2015

Charlie Chong/ Fion Zhang

Power Plant Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

Greek Alphabet

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

http://greekhouseoffonts.com/

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

Fion Zhang at Shanghai 5th August 2015

http://meilishouxihu.blog.163.com/

Charlie Chong/ Fion Zhang

IVONA TTS Capable.

Charlie Chong/ Fion Zhang

http://www.ivona.com/en/

My Mangoes

Charlie Chong/ Fion Zhang

Conductivity

Magnetic (Permeability & Dimensions)

A. Heat treatment give the metal

A. Length of the test sample

B. Cold working performed on the metal

B. Thickness of the test sample

C. Aging process used on the metal

C. Cross sectional area of the test sample

D. Hardness E. Crack & discontinuities

Charlie Chong/ Fion Zhang

FLT-Flux Leakage Testing

Charlie Chong/ Fion Zhang

FLT Level I Q&A

Charlie Chong/ Fion Zhang

Answers to Flux Leakage Testing Level I 1.c 2.c 3.a 4.c 5.b 6.d 7.b 8.a 9.d 10.a 11.b 12.a 13.b 14.d 15.d 16.d 17.a 18.a 19.a 20.d 21.b 22.b 23.c 24.c 25.c 26.d 27.c 28.c 29.b 30.c 31.b 32.a 33.b 34.a 35.a 36.c 37.c 38.d 39.a 40.b 41.a 42.b

Charlie Chong/ Fion Zhang

1. When using a detector coil, what is the primary condition required in order to obtain a signal from flux leakage? a. have many turns in the detector coil b. provide an electrical connection between the detector coil and the test part c. movement between the detector coil and the test object d. shielding the cable which connects the detector coil and the recorder A.157,388/G.317 Keywords: Detector coil!

For MFL-DC, either the test piece or the detector coil needs to be in motion to generate signal.

Charlie Chong/ Fion Zhang

2. Which of the following currents is appropriate for magnetization of the test object when doing flux leakage testing using detector coils? a. alternating current b. half wave current c. direct current d. spinning current D.7/G.267 Since early 1978, the high-energy alternating field stray flux method has gained in popularity for testing round ferromagnetic bars from 1 to 4.5 in. In diameter. With the Rotoflux AC magnetic flux leakage (AC-MFL) technique, a rotating head (Figure 3.14) containing the magnetizing yoke and sensitive pickup coils rotates as the bar stock is inspected at traverse speeds of 180 to 360 feet per minute (fpm). Figure 3.15 shows the cross section of a ferromagnetic bar being exposed to an alternating field between the pole pieces. Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M Section 3.2

Charlie Chong/ Fion Zhang

3.2 MAGNETIC FLUX LEAKAGE THEORY When ferromagnetic materials are magnetized, magnetic lines of force (or flux) flow through the material and complete a magnetic path between the pole pieces. These magnetic lines of flux increase from zero at the center of the test piece and increase in density and strength toward the outer surface.

When the magnetic lines of flux are contained within the test piece, it is difficult if not impossible to detect them in the air space surrounding the object.

However, if a crack or other defect disrupts the surface of the magnetized piece, the permeability is drastically changed and leakage flux will emanate from the discontinuity. By measuring the intensity of this leakage flux, we can determine to some extent the severity of the defect. Figure 3.9 shows magnetic flux patterns for a horseshoe magnet and flat bar magnet. Note the heavy buildup of magnetic particles is a three dimensional pattern at the poles.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Figure 3.9 Magnetograph of two permanent magnets in close proximity.

Magnetic lines of flux take the path of least resistance and bridge horseshoe magnet first.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

All of the fine magnetic particles near the magnets are drawn to the pole pieces and sharp edges of the magnets where leakage flux is strongest. At a greater distance, the circular nature of the magnetic lines of force can be more easily seen. The pattern for the horseshoe magnet shows weaker poles near the back curved portion of the magnet. The weaker poles were probably created as a result of the magnetizing technique used to initially magnetize the ferromagnetic material. The ideal permanent magnet should be easy to magnetize and hard to demagnetize. The ideal ferromagnetic test piece, inspected with flux leakage equipment, should be easy to magnetize and demagnetize. In practice, these ideal relationships are hard to achieve.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Based on what we have learned about magnetic flux leakage, Figure 3.10 illustrates that a notch or defect distorts the magnetic lines of flux causing leakage flux to exit the surface of the ferromagnetic material. If the material is not too thick (<0.3 in.), some flux may also exit the far surface. Figure 3.11 illustrates that with DC magnetic flux leakage (DC- FL) outer and inner cracks of equal magnitude produce similar, but opposite flux patterns and signals of differing width and amplitude when they are scanned from the outer surface of the test piece. Automatic flux leakage inspection systems use magnetic field sensors to detect and measure flux leakage signals. For longitudinal flaw detection on round bars and tubes, a rotational yoke DC- FL system is used.

The magnetic poles of the yoke are 180째 apart with a series of magnetic sensors 90째 from the poles as shown in Figure 3.12.The rotational yoke is fed with a direct current that produces a low- frequency AC field as the yoke rotates around the tube. By using a series of rotational heads, tubes with diameters of 0.4 to 25.0 in. can be tested.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Figure 3.10 Effect of radial crack or notch on longitudinal flux pattern.

Courtesy of Institut Dr. Foerster.

Figure 3.11 Effect on similar inner and outer defects on flux pattern and measurement. Courtesy of Institut Dr. Foerster.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Charlie Chong/ Fion Zhang

Figure 3.12 Rotating direct current magnetic yoke for establishing circular magnetic flux pattern to detect longitudinal defectsâ&#x20AC;&#x201D;Rotomat method. Courtesy of Institut Dr. Foerster.

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Flux leakage sensors have small diameters, some as small as 0.02â&#x20AC;?, in order to have adequate sensitivity for detecting short-length or small diameter defects. Because of their small size, the scanning head may have 16 or more sensors in order to achieve satisfactory throughput speeds. Probes are springloaded against the tube surface to provide fixed lift-off; they are lowered after the leading end of the tube is detected and raised just before the lagging tube end is reached. Signals from the probes on the inner and outer surfaces of the tube are transmitted through springs to the electronics unit where they are filtered and analyzed by a continuous spectrum analyzer. Inside and outside flaws are automatically marked by different-colored dyes that indicate the size and type of flaws detected. Transverse flaws are detected by passing the tube through a ring yoke that produces longitudinal magnetization. In this case, the tube surface is surrounded by and scanned with a ring of small probes. Signal processing and flaw marking is the same as previously described.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

When slower inspection speeds can be tolerated, a stationary yoke and spinning tube DC-MFL arrangement, shown in Figure 3.13, can be used. In this case, the inspection head is moved down the length of the tube to achieve a 100% surface inspection. It is relatively easy to combine other NDT techniques, such as ultrasonic testing, with this physical arrangement.

Since early 1978, the high-energy alternating field stray flux method has gained in popularity for testing round ferromagnetic bars from 1 to 4.5 in. In diameter. With the Rotoflux AC magnetic flux leakage (AC-MFL) technique, a rotating head (Figure 3.14) containing the magnetizing yoke and sensitive pickup coils rotates as the bar stock is inspected at traverse speeds of 180 to 360 feet per minute (fpm). Figure 3.15 shows the cross section of a ferromagnetic bar being exposed to an alternating field between the pole pieces.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

The frequency of the alternating field is about 1 to 30kHz, so that penetration of the magnetic flux is only a few tenths of a millimeter or few hundredths of an inch. With very-high-intensity alternating fields, requiring exciting yokes using kilowatts of power, the area of the rod near the surface and near the sides of the crack is magnetically saturated. Increases in intensity increase the depth of saturation. The permeability of the saturated areas approaches the permeability of air (one) while the inner areas of the bar, identified by the â&#x20AC;&#x153;xâ&#x20AC;&#x2122;sâ&#x20AC;?, have no magnetic flux and remain unchanged.

From a magnetic point of view, both the crack width and depth has been increased by the amount of saturation. In effect, this magnifies the effect of the defect and results in a very high signal-to-noise ratio that is easily detected by the pickup coil even on relatively rough bar surfaces.The probability of detecting a 0.01-in.-deep defect is 95% with both the Rotoflux and magnetic particle methods, but the magnetic particle test cannot be adapted for automatic, high-speed, in-line testing.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Figure 3.13 Direct current electromagnet scans length of rotating tube.

Circular flux pattern detects longitudinal defects. Courtesy of Institut Dr. Foerster.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Figure 3.14 Rotating magnet arrangement for detection of AC magnetic flux leakage current. Courtesy of Institut Dr. Foerster.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Figure 3.15 Measurement of AC magnetic flux leakage. Courtesy of Foerster Instruments, Inc.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

3. Flux leakage occurs in a ferromagnetic material when a discontinuity near the surface causes a disturbance of the magnetic field in the part: a. regardless of what created the magnetic field b. only if there is an active magnetizing force c. only if there is a residual magnetic field d. only if the magnetic field is a vector field D.7 4. Flux leakage inspection may be used on: a. ferromagnetic and non ferromagnetic materials b. nonferromagnetic materials only c. ferromagnetic materials only d. all conductive materials D.7

Charlie Chong/ Fion Zhang

5. Transverse magnetization in bar or pipe testing is used for the detection of: a. transverse discontinuities b. discontinuities that have a longitudinal component c. both transverse and longitudinal discontinuities d. only holes A.230 6. With flux leakage detection coil systems, the difference between similar OD and ID discontinuities is: a. signal amplitude b. impedance c. noise d. signal width and amplitude G.305/H.75

Charlie Chong/ Fion Zhang

7. An energized (magnetizing) coil around the part produces: a. a circular field b. a longitudinal field c. an intermittent field d. a field direction dependent on the type of current applied 0.44

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

8. Using Figure 16, what is the normal (vertical) component of the leakage flux at the middle of the wide discontinuity gap of a surface discontinuity? a. zero b. maximum c. equal to the horizontal component d. divergent e. convergent A.235

Bx

Charlie Chong/ Fion Zhang

9. Flux leakage techniques can normally be used to test for: a. surface discontinuities only b. subsurface discontinuities only c. discontinuities at any location d. surface and near-surface discontinuities D.39 6. With flux leakage detection coil systems, the difference between similar OD and ID discontinuities is: a. signal amplitude b. impedance c. noise d. signal width and amplitude G.305/H.75

Charlie Chong/ Fion Zhang

3.14 MAGNETIC FLUX LEAKAGE TESTING The magnetic flux leakage method is dry, fast, online, and recommended by the American Petroleum Institute for tubes with small to medium wall thickness. Magnetic flux leakage testing is of great importance for process reliability and quality control assurance in the production of oil field and boiler tubes.

Magnetic flux leakage tests help assure the safety of nuclear and conventional power plants, offshore platforms, the oil and gas industries, and chemical and petrochemical plants. DC field magnetization is used over the entire cross section of pipes transversely using Rotomat速 and longitudinally using Transomat速 (Figure 3.35), thereby providing simultaneous testing for internal and external flaws. With appropriate with state-of-the-art filtering and signal gating, separate indications are provided for internal and external flaws.

When testing with external sensors, internal flaws have lower peak height and longer wavelength.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

Level II Q&A 16. In flux leakage testing, the greatest tube wall thickness for which maximum sensitivity can be maintained is: a. 0.08 mm (0.003 in.) b. 0.8 mm (0.03 in.) c. 8 mm (0.318 in.) d. 76 mm (3 in.)

D.111

Charlie Chong/ Fion Zhang

10. A relative motion between the test piece and a ____ is needed in order to detect leakage flux. a. detector coil b. hall effect element c. magneto probe d. piezoelectric crystal A.157,388

Charlie Chong/ Fion Zhang

11. More magnetic lines of force are deflected out of a magnetized ferrornagnetic material when the: a. length of the crack is parallel to the magnetic lines of force b. length of the crack is perpendicular to the magnetic lines of force c. length of the crack is diagonal to the magnetic lines of force d. edges of the crack are polarized A.48/E.4 12. Magnetic properties of a ferromagnetic material are depicted by the: a. hysteresis loop b. minor loop c. recoil curve d. magnetization curve e. permeability curve D.45

Charlie Chong/ Fion Zhang

13. The line shown in Figure 17 is the: a. residual field line b. virgin curve c. remagnetization line d. flux leakage line D.45

Figure 17

Charlie Chong/ Fion Zhang

14. A hall effect probe measures: a. permeability b. conductivity c. tangential field strength d. flux density perpendicular to the probe surface e. reluctance D.50 15. The ratio between the flux density and the magnetic field strength (B/H ratio) is the: a. field strength b. reluctance c. permittivity d. permeability e. relative saturation D.47

Charlie Chong/ Fion Zhang

16. If the part in Figure 18 has a circular magnetic field, which of the discontinuities would give the best indication with a rotating flux detection system? a. A b. B c. C d. D A.240

Charlie Chong/ Fion Zhang

17. If the part in Figure 18 has a longitudinal magnetic field, which of the discontinuities would give the best indication with a detector coil orientated across the part? a. A b. B c. C d. D E.14 18. The best angle for the magnetic field to intersect a discontinuity in a test specimen is: a. 90째 b. 60째 c. 45째 d. 30째 A.230/G.289

Charlie Chong/ Fion Zhang

19. In the flux leakage examination of tubular products using rotating sensor coils, which of the following discontinuities can be detected? a. longitudinally oriented b. transversely oriented c. slivers d. laminations G.254 20. In flux leakage testing using search coils, the amplitude of the signal received from a discontinuity may be affected by: a. the depth of the discontinuity b. the orientation of the discontinuity c. the distance between the flux leakage sensor and the tube d. all of the above e. only a and c A.157 /G.323

Charlie Chong/ Fion Zhang

21. Which of the following describes the type of magnetic field created in a pipe by using an encircling magnetizing coil? a. circular b. longitudinal c. vector d. retentive reversal A.231 22. After the pipe leaves an encircling coil, it has which of the following magnetic fields? a. active longitudinal b. Residual longitudinal c. active residual d. transverse A.231

Charlie Chong/ Fion Zhang

23. The width and amplitude (height) of the signals induced in the search coils are affected by which of the following? a. the amount of voltage induced into the test part by the magnetizing coil b. the electrical resistance of the test part material c. the rate of change in the flux leakage as seen by the detector coil d. the amount of current induced into the test part by the magnetizing coil A.388 Comments: Amplitude ∝∆Ф ?

Charlie Chong/ Fion Zhang

24. Generally, when comparing a detector coil signal from a crack and a corrosion pit, which of the following characteristics would indicate that the signal is caused by a crack? a. wide base, high amplitude b. narrow base, low amplitude c. narrow base, high amplitude d. wide base, low amplitude A.388

Charlie Chong/ Fion Zhang

25. Generally, when comparing a hall effect detector signal from a crack and a corrosion pit of the same depth: a. the crack will produce a higher amplitude b. the pit will produce a higher amplitude c. they will produce signals of approximately the same amplitude d. cracks can not be detected by hall effect detectors A.154

Charlie Chong/ Fion Zhang

26. A detector coil that is shorted: a. will reduce any signals by about 25% b. will reduce any signals by about 50% c. will reduce any signals by about 75% d. will cause the signals to be eliminated from the shorted coil D.49 27. Which of the following has the most effect on the amplitude of a rotating detector coil signal? a. drive roller speed b. pipe speed c. rotating head speed d. polarity switch setting A.240

Charlie Chong/ Fion Zhang

28. In a flux leakage test, assuming that all of the following are in the same relative position, which would be the hardest to detect? a. a surface crack b. a near-surface crack c. a scratch d. a seam A.388 29. Magnetic flux lines that are parallel to a discontinuity produce: a. strong indications b. weak indications c. no indications d. fuzzy indications 8.16

Charlie Chong/ Fion Zhang

30. Magnetic lines of force: a. travel in straight lines b. are randomly oriented c. form a closed loop d. overlay in highly ferromagnetic materials B.12 31. A metal that is difficult to magnetize is said to have: a. high permeability b. low permeability c. high reluctance d. low retentivity B.45

Charlie Chong/ Fion Zhang

32. The magnetism that remains in a piece of magnetizable material after the magnetizing force has been removed is called the: a. residual magnetism b. tramp magnetism c. damped magnetism d. permanent magnetism B.25 33. Flux leakage inspection is not a reliable method of detecting: a. laps b. deep internal cavities c. cracks d. seams 8.233

Charlie Chong/ Fion Zhang

34. Ferromagnetic material is: a. strongly attracted by a magnet 路 b. not highly saturated by magnetic fields c. a material with a 0 permeability measurement d. not capable of being magnetized D.138 35. An electric current through a copper wire: a. creates a magnetic field around the wire b. creates magnetic poles in the wire c. magnetizes the wire d. does not create a magnetic field 8.18

Charlie Chong/ Fion Zhang

36. If a current is passed through an electrical conductor, what will surround the conductor? a. an eddy current field b. a current c. a magnetic field d. a residual field B.18 37. The strength of the magnetic field induced in a part is often referred to as: a. current density b. voltage c. flux density d. retentivity B.15

Charlie Chong/ Fion Zhang

38. Indications such as those at local vent holes or welds are: a. fake indications b. relevant indications c. magnetic writing indications d. nonrelevant indications B.234 39. Which of the following statements is a disadvantage of flux leakage testing? a. it can be used only on ferrous materials b. it can be applied only to detect surface discontinuities c. it can be applied only to detect subsurface discontinuities d. it can only detect discontinuities parallel to the magnetic field B.2

Charlie Chong/ Fion Zhang

40. The direction of a magnetic line of force is ____ degrees from the direction of current flow. a. 45 b. 90 c. 180 d. 220 B.19 41. Stopping the detector coil directly over a discontinuity will cause the signal to: a. stop b. increase c. go the opposite direction d. stay the same A.388

Charlie Chong/ Fion Zhang

42. If a periodic standardization check is unacceptable, what action should the operator take? a. repeat the check without adjustment b. restandardize and reexamine all pipe run since the last acceptable check c. restandardize and reexamine all pipe with signals over fifty percent of reference run since the last acceptable check d. restandardize and reexamine all pipe run that day e. restandardize and continue the inspection with the next joint F.E-570.5

Charlie Chong/ Fion Zhang

Recalling the mistakes

Charlie Chong/ Fion Zhang

Flux Leakage Testing Level II Q&A

O TW

Charlie Chong/ Fion Zhang

Answers to Flux Leakage Testing Level II

Charlie Chong/ Fion Zhang

1. In flux leakage inspection of wire ropes using an encircling coil as a sensor, the response of the coil depends on what parameters of the wire break? a. the cross-sectional area of broken wire b. the location of broken wire within the cross section c. the gap between the ends of fhe broken wire d. all of fhe above A.430 2. The highest sensitivity of a hall generator is obtained when fhe direction of the magnetic field in relation to the largest surface of the hall probe is: a. parallel b. at an angle of 45" c. perpendicular d. none of the above A.153

Charlie Chong/ Fion Zhang

3. The best discontinuities detection sensitivity is obtained when the magnetizing flux is: a. parallel to the discontinuity's longest dimension b. perpendicular to the discontinuity's shortest dimension c. perpendicular to the discontinuity's longest dimension d. none of the above A.230/G.289 4. In flux leakage inspection for discontinuities using an active field, the part being inspected should be magnetized: a. beyond saturation b. to saturation or near saturation c. well below saturation d. near the point of maximum permeability A.49

Charlie Chong/ Fion Zhang

5. An advantage that flux leakage testing has in comparison with eddy current testing is that flux leakage testing is: a. less sensitive to interferences caused by surface roughness b. useful on products at temperatures above the curie point c. useful on austenitic steels d. easier to use on ferromagnetic materials A.47

Charlie Chong/ Fion Zhang

6. Using Figure 19, flux leakage strengfh decreases with distance d from the discontinuity surface and is approximately proportional to: a. d b. 1/d c. 1/d2 d. 1/d3 e. 1/d4 H.95

Charlie Chong/ Fion Zhang

7. Using Figure 20, which notch would produce the highest amplitude signal when using a parallel coil or a pair of hall elements connected in opposition? a. A b. B c. C d. D G.327 Amplitude â&#x2C6;? Depth/Width ?

Charlie Chong/ Fion Zhang

7. Using Figure FL-6, the relation between the depth (D) of defects and signal amplitude (A) of leakage flux is approximately (K = constant of proportionality): a. A =k 1/D b. A =kD c. A =kD2 d. A =kD3 e. A =kD4 L.54 Amplitude â&#x2C6;? Depth, Amplitude â&#x2C6;? 1/W, Amplitude = kD/W Figure FL-6

W

Charlie Chong/ Fion Zhang

17. The field strength over a crack is directly proportional to the relative permeability of the steel and the ratio: a. crack depth/crack wtdth b. crack width/crack depth c. crack length/crack depth d. crack length/crack wtdth X.194 B â&#x2C6;? D/W ?

D W

Charlie Chong/ Fion Zhang

8. What particular type of discontinuity would not typically be indicated by flux leakage techniques? a. laps b. pitting with cracking c. surface contamination d. longitudinal seams A.239 9. The strength of the magnetic field in the interior of a coil is determined by: a. the number of turns in the coil only b. the strength of applied current only c. the number of turns in the coil and the strength of the applied current d. the direction of applied current in the coil A.231

Charlie Chong/ Fion Zhang

10. If the sensor bounces along the surface of above-ground storage tanks, it may: a. make it difficult to estimate fault severity b. generate noise in the signal c. decrease the speed of the inspection d. distort the magnetizing system A.388 11. In flux leakage testing, the advautage(s) of electromagnetic magnetization over permanent magnets is/are: a. Non adjustable magnetic field intensity, lighter, more rugged construction b. adjustable magnetic field intensity, heavier, more rugged construction c. adjustable magnetic field intensity d. nonadjustable magnetic field intensity and lighter A.388

Charlie Chong/ Fion Zhang

12. The current used for magnetization when doing magnetic flux leakage inspection must be a: a. steady non fluctuating current (DC) b. current that reverses direction at a consistent rate c. current that fluctuates on and off at a consistent rate d. current that varies based on the thickness of the material A.387 13. As a general rule, hard (high strength) ferromagnetic materials have: a. high coercive force and are easily demagnetized b. high coercive force and are not easily demagnetized c. low coercive force and are easily demagnetized d. low coercive force and are not easily demagnetized e. none of the abOve E.41

Charlie Chong/ Fion Zhang

14. The point P shown on the hysteresis loop in Figure 21 is called the: a. coercive force b. initial permeability c. residual field (Remanence) d. leakage flux e. demagnetization point E.40

Charlie Chong/ Fion Zhang

15. The bracketed area shown by R on the hysteresis loop in Figure 21 is called the: a. coercive force b. initial permeability c. residual field d. leakage flux e. demagnetization point E.40 16. In flux leakage testing, the greatest tube wall thickness for which maximum sensitivity can be maintained is: a. 0.08 mm (0.003 in.) b. 0.8 mm (0.03 in.) c. 8 mm (0.318 in.) d. 76 mm (3 in.)

0.111

Charlie Chong/ Fion Zhang

Keypoints: MFL       

Only applicable to ferromagnetic material DC-MFL predominantly Near magnetic saturation of test piece is necessary Permanent magnet or DC electro-magnetization Effective detection limit is 0.3” (8mm) Circumferential (transverse) field Longitudinal (axial) field

Charlie Chong/ Fion Zhang

17. The following may be used to detect flux leakage: a. inductive sensor coils b. magnetic tape c. hall element(s) d. all of the above D.49-53 18. In the examination of tubular products, a circumferential (transverse) magnetic field can be established by: a. properly positioning north and south poles of a yoke with respect to the tube b. using a central conductor positioned in the tube c. passing current through the tube d. all of the above e. a and b only A.230-232

Charlie Chong/ Fion Zhang

19. In the examination of above-ground storage tanks where the flux sensor is on the top surface: a. only top surface discontinuities are detected b. only bottom surface discontinuities are detected c. both top and bottom surface discontinuities can be detected but generally cannot be distinguished from each other d. both top and bottom surface discontinuities can be detected and can generally be distinguished from each other A.389

Charlie Chong/ Fion Zhang

Level II Flux Leakage Testing 23. In the examination of tubular products where the flux sensor measures the leakage field at the outside surface of the tube: a. OD discontinuities are detected b. both OD and ID discontinuities may be detected c. both OD and ID discontinuities can be detected but generally cannot be distinguished from each other d. both OD and ID discontinuities can be detected and can generally be distinguished from each other DD.625

Charlie Chong/ Fion Zhang

20. Reference standards used in the flux leakage examination of tubular products should be carefully prepared since the flux leakage signal response from the notch will be affected by: a. notch width b. notch length c. notch depth d. all of the above A.277 21. Which of the following is not a discontinuity common to rolled products? a. seams b. cracks c. cold shuts d. laminations E.110

Charlie Chong/ Fion Zhang

22. Forging laps occur in what relation to the axial direction of a part? a. they are always found on the thermal centerline b. they are found on the surface of a part at a 90째 angle to the long axis c. they may occur anywhere in the part and always run in the direction of working d. they may occur anywhere on the surface and may bear no relation to the axial direction of the part E.115 23. The general term used to refer to a break in the metallic continuity of the part being tested is: a. discontinuity b. crack c. seam d. lap E.109

Charlie Chong/ Fion Zhang

24. Materials which are weakly repelled magnetically are called: a. diamagnetic b. nonmagnetic c. paramagnetic d. ferromagnetic E.6 25. A break in the magnetic uniformity of a part that is called a magnetic discontinuity is related to a sudden change in: a. resistivity b. inductance c. permeability d. capacitance D.101

Charlie Chong/ Fion Zhang

26. A hysteresis curve describes the relation between: a. magnetizing force and flux density b. magnetizing force and applied current c. strength of magnetism and alignment of domains within material d. magnetic flux density and the current generated E.39 27. Inclusions are an example of which kind of discontinuity? a. inherent b. primary processing c. secondary processing d. service 8.76

Charlie Chong/ Fion Zhang

28. Fatigue cracking is an example of which kind of discontinuity? a. inherent b. primary processing c. secondary processing d. service B.80 29. Hot tears are associated with: a. casting b. forging c. welding d. rolling 8.78

Charlie Chong/ Fion Zhang

30. When inspecting wire rope, a magnetic flux loop is used to monitor: a. broken external wires b. broken internal wires c. changes in inspection speed d. reductions in cross-sectional area B.80 31. The characteristics of the varying magnetic field about an AC energized coil are determined by: a. the number of turns in the coil b. the strength of applied current c. the size and shape of the solenoid d. all of the above C.307

Charlie Chong/ Fion Zhang

32. Flash line tears are associated with: a. casting b. forging c. welding d. rolling B.78

Charlie Chong/ Fion Zhang

H. Burning.

Overheating of forgings, to the point of incipient melting, results in a condition which renders the forging unusable in most cases, and is referred to as burning. However, the real source of the damage is not oxidation, but the material becoming partially liquefied due to the heat at the grain boundaries. Burning is a serious defect but is not generally shown by magnetic particle testing.

I. Flash Line Tears.

Cracks or tears along the flash line (see Glossary) of forgings are usually caused by improper trimming of the flash. If shallow they may "clean up" during machining. Otherwise they are considered defects. Such cracks or tears can easily be found by magnetic particles. (See Figure 3-61.)

Charlie Chong/ Fion Zhang

http://chemical-biological.tpub.com/TM-1-1500-335-23/css/TM-1-1500-335-23_299.htm

Flash The excess metal that flows out between the upper and lower dies which is required to accomplish a desired forging shape.

Flash Line The line where the flash occurs. http://www.engr.sjsu.edu/minicurric/images/lecture_powerpoints/ForgingTerminology.pdf

Figure 3-61. Magnetic Particle Indication of Flash Line Tear in a Partially Machined Automotive Spindle Forging.

Charlie Chong/ Fion Zhang

http://chemical-biological.tpub.com/TM-1-1500-335-23/css/TM-1-1500-335-23_300.htm

Forging of Crank Shaft

Charlie Chong/ Fion Zhang

Recalling the mistakes

Charlie Chong/ Fion Zhang

Flux Leakage Testing Level III Q&A

e e r Th

Charlie Chong/ Fion Zhang

1. Which of the following flux sensitive devices is not time dependent? a. long straight wire passing through a magnetic field b. search coil c. search coil derivative d. hall element B.143

Charlie Chong/ Fion Zhang

2. In Figure 22, the signal produced in a search coil with its plane parallel to the part surface by slot A will be ______ that at slot B. a. greater in amplitude than b. the same amplitude as c. a lower amplitude than d. wider than A.235 Figure 22

Charlie Chong/ Fion Zhang

4. In Figure FL-10, the flux leakage at slot A will be____ than that at slot B. a. greater b. Smaller A â&#x2C6;? D/W c. broader d. less readily detected z.so FL-10

Charlie Chong/ Fion Zhang

17. The field strength over a crack is directly proportional to the relative permeability of the steel and the ratio: a. crack depth/crack wtdth b. crack width/crack depth c. crack length/crack depth d. crack length/crack wtdth X.194 B â&#x2C6;? D/W ?

D W

Charlie Chong/ Fion Zhang

3. Which devices are used to detect flux leakage? a. coils, hall probes and transistors b. piezoelectric crystals, hall probes and magnetic diodes c. piezoelectric crystals, transistors and magnetic diodes d. coils, hall probes and magnetic diodes G.311

Charlie Chong/ Fion Zhang

4. In the flux leakage testing of wire rope, a system using an annular coil with integrator is frequently used (see Figure 23). What is the main reason for using such a system? a. to compensate for the influence of testing speed variations b. to find the radial location of wire breaks c. to detect small cracks inside the rope d. to detect cross-sectional area changes A.438

Charlie Chong/ Fion Zhang

5. In a properly operating flux leakage test system, pipe discontinuities occurring at increased depths from the surface will generate signals with: a. increased phase differences b. higher frequency characteristics c. lower frequency characteristics d. increased signal to noise ratios A.235 Udpa, S.S., tech. ed., P.O. Moore, ed. Nondestructive Testing Handbook, third edition: Vol. 5, Electromagnetic Testing. Columbus, OH: The American Society for Nondestructive Testing, Inc. (2004).

Charlie Chong/ Fion Zhang

ď Ž 3.10 EDDY CURRENT TECHNIQUES When outside encircling coils are used for testing, the phase of the outer surface discontinuities will lead the phase of identical inner surface discontinuities. For best results with encircling coils, inspection coil length, the desired resolution, and test frequency are used to determine the maximum velocity of inspected tubing.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

6. Lift-off reduces the amplitude of the flux leakage signal. The other significant effect it has on the signal is a: a. change in phase b. change in frequency c. change in signal to noise ratio d. all of the above G.320

Charlie Chong/ Fion Zhang

ď Ž 3.6 SIGNAL-TO-NOISE RATIO With flux leakage testing, signal-to-noise ratio is affected by surface noise (the sensor bouncing along the surface) and probe lift-off variations. Lift-off decreases the amplitude of the flux signal and changes its frequency.

Spring loaded probes can help minimize these effects.Too high a rotational test speed or too high a rotating probe head speed can also cause a loss of test indication by eddy current shielding ď Ž 3.9 COUPLING As lift-off or probe clearance increases from the test surface, coupling efficiency and eddy current probe output decreases. Lift-off changes both the amplitude and phase of the eddy current signal. Impedance changes produced by small lift-off variations are greatest when the coil is in contact with the test material. For this reason, spring-loaded probes and selfcomparison coil or differential coil arrangements are frequently used.

With eddy current testing, lift-off is a complex variable that can be detected and compensated for through frequency selection to achieve a desirable operating point on the complex impedance plane.

Charlie Chong/ Fion Zhang

Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M

7. As shown in Figure 24, a discontinuity having an inclined angle to the surface has a flux leakage that is: a. lower than a similar normal discontinuity b. equal to a similar normal discontinuity c. higher than a similar normal discontinuity d. all of the above B.140

Charlie Chong/ Fion Zhang

8. Eddy current shielding, the name given to the unidirectional eddy current flow in products inspected by flux leakage testing, is caused by: a. the interaction between the test magnetic field and a residual field in the product b. fluctuations in the DC magnetizing current c. rapidly occurring flux changes in the product created by the rotation of the magnetic field d. rapidly occurring impedance changes in the pick-up coils G.280 9. Too high a rotational test speed or too high active pole rotating head speed can cause the loss of an indication from an ID discontinuity: What can this be attributed to? a. excessive generated surface noise b. limitations of the flux sensor elements c. eddy current shielding d. reverse magnetization effect G.280

Charlie Chong/ Fion Zhang

For questions 10 and 11, use the following formula: Linear speed (per minute)= RPM x detectorlength x number of detectors / percent coverage Note: detector length and linear speed must be the same units (in., ft, m).

10. A flux leakage test pipe inspection system with two inspection heads, each having 152 mm (6 in.) long scan paths and rotating at 180 rpm on a 178 mm (7 in.) diameter tube, can have a maximum throughput speed of per minute for 100% inspection coverage. a. 201 rn (660ft) b. 55 m (180ft) 152 x 2 x 180 = 54720mm c. 49 m (162ft) d. 27 m (90ft) I.564,571/J.22A

Charlie Chong/ Fion Zhang

11. A flux leakage pipe inspection system with two inspection heads, each having 152 mm (6 in.) long inspection areas and rotating at 180 rpm on a 178 mm (7 in.) diameter pipe, would require a throughput speed of per minute to provide a 110% inspection coverage. a. 60 m (198ft) b. 49 m (162ft) c. 45 m (146ft) d. 25 m (81ft) e. 22 m (73ft) I.564,571/J.22A 2 x 152 x 180 /1.1 = 49745mm (2 x 6 x 180/1.1)/12 = 163ft

Charlie Chong/ Fion Zhang

12. What has the most influence on the magnetic properties of steel? a. chemistry, microstructure and grain size b. cross-sectional area, microstructure and heat treatment c. cross-sectional area, grain size and chemistry d. heat treatment and length B.56 Comments: Cross sectional area will have not effect on the permeability! Although it might affect apparent permeability of the test piece during testing and this is term noise.

Charlie Chong/ Fion Zhang

13. A current carrying conductor is surrounded by a tube (see Figure 25).

There will be a magnetic flux line, while the current is on, in which of the following materials? a. steel b. copper c. aluminum d. all of the above B.127

Charlie Chong/ Fion Zhang

14. What is the SI unit for magnetic flux density? a. weber b. gauss c. tesla d. none of the above A.24 15. What is the SI unit for magnetic field strength? a. weber (magnetic flux) b. tesla (magnetic density) c. ampere d. ampere per meter (magnetic field intensity) A.24

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

16. When inspecting wire rope, the annular coil approach measures: a. the magnetic flux in the rope locally b. the normal component of flux leakage c. the tangential component of flux leakage d. the voltage induced in the rope locally A.439

Charlie Chong/ Fion Zhang

17. A tube is magnetized by passing a uniform current through the tube.

There are inside and outside discontinuities in the tube (see Figure 26). The two discontinuities have the same dimension and geometry. The signal: a. will be stronger from the outside discontinuity b. will be stronger from the inside discontinuity c. will be the same for both discontinuities d. will be stronger from either discontinuity based on the geometry of the discontinuity, wall thickness and permeability of the tube D.101

Charlie Chong/ Fion Zhang

18. A ferromagnetic part can be demagnetized by: a. raising its temperature above the curie point b. withdrawing the part from an AC coil c. alternately reversing and reducing the applied field d. all of the above E.79 19. In the flux leakage inspection of aboveground storage tanks, the factor(s) that must be considered when interpreting an indication is/are: a. signal amplitude only b. signal width only c. visual and ultrasonic evaluation d. signal amplitude and width A.389

Charlie Chong/ Fion Zhang

20. Permeability of a material can be numerically written as: a. R/B b. B/H c. Hc/Hb d. ampere turns/number of turns D.47 21. Magnetic field intensities for electronic flux leakage testing generally ____ magnetic particle testing. a. are higher than for b. are the same as for c. are lower than for d. have no relationship to B.142

Charlie Chong/ Fion Zhang

22. Which of the following is not a factor in determining flux leakage? a. discontinuity location with respect to the measurement surface b. relative permeability of the materials c. levels of magnetic field intensity d. density of the material A.238 23. The sensitivity of a pickup coil is improved by: a. lengthening the coil b. widening the coil c. using a ferrite core d. using a diamagnetic core A.236

Charlie Chong/ Fion Zhang

24. The only component of the flux leakage detected by a search coil is: a. parallel to the axis of the coil (or perpendicular to the plane of the coil) b. perpendicular to the axis of the coil (or parallel to the plane of the coil) c. the 45째 vector field d. the internal field normal to the axis of the coil A.235 25. The reduction in cross-sectional area caused by a discontinuity causes: a. an increase in the internal flux density of the part b. a decrease in the internal flux density of the part c. no change in the internal flux density of the part d. a reversal of direction in the magnetic field at the reduction in crosssectional area A.48

Charlie Chong/ Fion Zhang

26. When using search coils, to reduce or eliminate the signal from a long nonrelevant indication such as the weld trim of electric welded pipe: a. lengthen the coil b. widen the coil c. use a ferrite core d. link two coils wound in opposite directions in series G.323

Charlie Chong/ Fion Zhang

Recalling the mistakes

Charlie Chong/ Fion Zhang

Reading 1: Magnetic NDT of Steel Wire Ropes Kazimierz Zawada Zawada NDT, Tatarkiewicza 8, 41-819 Zabrze, Poland

Charlie Chong/ Fion Zhang

http://ndt.net/article/v04n08/zawada/zawada.htm

Abstract Magnetic NDT of wire ropes has been in regular use in a number of countries for inspection of hoisting ropes in deep mines and inspection of ropeways.

Recently used method is based on magnetization of the rope with permanent magnets and detection of the changes of magnetic field around the rope and total magnetic flux. â&#x2013; Discontinuity in the rope, such as broken wire or corrosion pit creates radial magnetic flux leakage and sensor detects it as the rope passes trough the sensing head. â&#x2013; Other sensor measures total axial magnetic flux in the rope. It provides information about loss of steel due to missing wire, continuous corrosion or abrasion.

Using magnetic method a rope expert have a possibility to estimate the rope condition. In conjunction with visual examination this method may be applied to determine the moment when the rope should be discarded. Various equipment for different application ranges is available.

Charlie Chong/ Fion Zhang

Permanent magnet method

Charlie Chong/ Fion Zhang

Although magnetic NDT of wire ropes has been in regular use in a number of countries for 30 or more years, it is still not commonly known NDT method.

This method is well known and recognised in application areas such as inspection of hoisting ropes in deep mines and inspection of ropeways.

Equipment recently used for non-destructive testing of steel wire ropes generally uses the same method, "permanent magnet method". The method is based on magnetisation of the rope with permanent magnets and detection of rope anomalies indirectly by magnetic sensors. This method is somewhere called "DC" magnetic method because of previously used Direct Current excitation coils, opposite to previously used Alternating Current coils (outdated AC method).

Since very first introduction in Poland (at AGH university), for latest over 20 years almost all manufacturers supply sensing heads where permanent magnets longitudinally magnetise a length of rope as it passes trough the head. A constant magnetic flux that magnetises the rope must be strong enough to create condition near magnetic saturation of the rope length.

Charlie Chong/ Fion Zhang

Various types of sensors have been applied by some manufacturers of instruments across the world. Sensors provide different signals depending on the design of the magnetic concentrators and type, number and location of sensing devices.

Inductive coils and/or Hall generators are popularly used as sensing devices.

However generally, due to its application concept, sensors can be divided into two types: LF sensors, i.e. Local Fault or Local Flow sensors; LMA sensors, i.e. Loss of Metallic cross-sectional Area

Charlie Chong/ Fion Zhang

LF sensors LF type discontinuity in the rope, such as broken wire or corrosion pit creates radial magnetic flux leakage and LF sensor detects it as the rope passes trough the sensor. LF sensor is placed coaxially around the rope, centrally between magnetic poles of the magnetising circuit. Its signal is rather qualitative then quantitative. However this signal provides information about presence of local fault and also more or less information about its magnitude.

LMA sensor LMA sensor measures total axial magnetic flux in the rope as an absolute magnitude or variations in a steady magnitude of the magnetic field. This signal is proportional to the volume of steel or the change in steel crosssectional area. It provides information about loss of steel due to missing wire, continuous corrosion or abrasion. LMA sensors are located in various places, almost within magnetising circuit or nearby it. When absolute value is displayed it is somewhere called TCMA, i.e. "total change of metallic area".

If an NDT instrument is designed to detect primarily either LF or LMA, but not both, it is called "single function" instrument. "Dual function" instrument detects both, separately.

Charlie Chong/ Fion Zhang

Limitations of magnetic method This method is limited to the testing of ferromagnetic steel ropes. Although usefulness of magnetic NDT of wire ropes is inestimable, this method should be supplemented with other examinations, especially with visual method.

Rope should be tested periodically since its installation date. Magnetic test gives basic information about rope condition. Instrument indicates defected places on the rope length. Using magnetic method a rope expert have a possibility to estimate the rope condition. However he should employs also other methods to evaluate the condition of a rope when must say whether the rope should be discarded.

The user must take into consideration which way the instrument indicates loss of the rope area (LMA). Usually the indications should be corrected by calculations, referred to rope construction type and observed deterioration.

Charlie Chong/ Fion Zhang

LF signals generated by internal broken wires and internal wear are sometimes disturbed by signals generated by external non-uniform wear.

Internal broken wires accumulated close to each other generate complex signal which amplitude depends on its distribution and number. Sometimes, these relations are greatly complex and precise identification is difficult to do.

If a rope is tested periodically since its installation date using magnetic method the inspector is able to observe successively increasing number of broken wires and other defects. This way results of non-destructive test are easiest to interpretation then performed first time when the number of broken wires is great and broken wires are accumulated.

Charlie Chong/ Fion Zhang

Equipment Two categories of equipment to test ropes have been supplied: ď Ž simplified auxiliary testers for detecting and indicating localised flaws or loss of metallic cross-sectional area with a light flash or an acoustic signal;

FIG1: MD-20 Wire Rope Tester

Charlie Chong/ Fion Zhang

ď Ž high-end instrumentation with strip chart and/or computer recording which is capable of estimating loss of metallic cross-sectional area and localised losses, and features the real aid to determine true deterioration of the rope.

FIG 3. MD120 chart recorder

Charlie Chong/ Fion Zhang

Fig2. GP-series sensing head

Charlie Chong/ Fion Zhang

The second category of instrumentation is intended to perform detailed tests.

In conjunction with visual examination they may be applied to determine the moment when the rope should be discarded. Generally this instrumentation consists of two units: a sensing head; and a signal processing/recording instrument. Sometimes the signal processing part and a standard chart recorder are supplied as separate units. Now some suppliers offer portable computers and software for use instead of chart recording. Detectability of rope defects depends mainly on the sensing head employed but readability of its signals and ease of operation depend mainly on recording/processing instrument.

The sensing head brings the running sector of wire rope to the condition close to magnetic saturation and senses magnetic fields. All reputable manufacturers employ at least double-channel sensing system: one to detect localised losses (LF), and the other one to detect the distributed loss of metallic cross-sectional area (LMA or TCMA). Only some types of Polishmade and German heads are equipped with additional channels to estimate the depth inside the rope of a localised loss position.

Charlie Chong/ Fion Zhang

Detecting capabilities of sensing heads vary between manufacturers and rope constructions. They depend on strong magnetisation capability, shape of magnetic concentrators in the sensor and operating principle of the sensor. In order to measure running rope length (and speed of relative movement), some manufacturers supply heads equipped with special transducer for indicating rope/head movement as an electric signal. Some manufacturers use it to synchronise the strip chart feed with the rope/head travel. This signal is also useful to compensate the speed influence on the inductive coil signal.

FIG2: GP-series sensing head Processing electronics depends on the sensor types and equipment features. For example the Hall generator sensor requires supply control and compensation of DC component of its signal, and the inductive sensor signal needs rope speed compensation to achieve good performance of the instrumentation. Some instruments have additional circuits that make them more convenient in use, e.g. rope length/speed measuring circuits.

Charlie Chong/ Fion Zhang

A strip chart recorder seems to be indispensable in each fully functional wire rope NDT instrument, as a third part of an instrumentation set, or integrated with the electronic processing part of the equipment. Mostly, manufacturers of these NDT instruments use standard, stand-alone or OEM unit recorders.

Almost, it is a two-channel digital thermal array printer or sometime analogue pen recorder. A recorder appropriate for this sort of application must be equipped with drive control to achieve good correlation between the recording and the wire rope at any non-controlled rope speed, within test speed range.

The recording should be performed at real time mode, instantly. Meraster MD120 Defectograph is an example of extremely task dedicated recording instrument.

In addition, specialised computer software is supplied as an extension of the equipment capabilities. However some manufacturers supply software and notebooks instead of chart recording instruments. This way seems to be easier today but mainly for suppliers. Actually, most of NDT users prefer instant ease readable strip chart recording then signal runs displayed on notebook screen.

Charlie Chong/ Fion Zhang

Meraster MD120 Wire Rope Defectograph Based on many years of previous experience, the first model of this instrument was introduced in 1994. Since this date MD120 series has been supplied to rope experts in Poland and around the world and it has been recognised as a valuable state-of-art instrument Apart from the standard features of reliable instrumentation, mentioned above, the unique features of the MD120 Defectograph are: capability of determining the rope defect depth location inside the rope; running integral method for easy read out of high density of defects; zoom replay of recording; solid state memory (computer compatibility); automatic printing of annotations; automatic set up after entering the specific rope code ("settings + rope code" memory).

Charlie Chong/ Fion Zhang

The Defectograph equipped with a suitable sensing head with a threechannel sensor, records test signals in four measurement channels. Two channels of inductive sensors (inner and outer coils) are intended for detecting "localised losses". Relation between recorded values in both these channels indicates depth of the defect position inside the rope. Channel of Hall-effect sensor signal is provided for detecting of "distributed loss of metallic cross-sectional area"; Fourth channel, integral of the main inductive sensor (inner coil) signal is intended for indicating the totalled "localised losses" along a rope sector.

Charlie Chong/ Fion Zhang

Fig 4: Example of a Wire rope test chart This last channel needs some explanation to understand its unique role. There are two advantages of this recording, particularly for mining hoist ropes, where broken wires are concentrated. First, more readable indication of a real damage resulting from broken wires, located close to each other, than in "localised losses" channel. Second, set-up of integration range in instrument according to rope discard criteria "number of broken wires in any x diameter length" allows indicating total losses in appropriate rope sectors lengths.

Charlie Chong/ Fion Zhang

The instrument operates continuously, in the "running integration" mode, where integration is being performed on a length in the next rope sector. The instrument is recording current values of the integral (total of losses) of previous rope sector, last "x" metres length. If the length of integration range is set appropriate to discard criteria, it gives direct readable indications of rope sectors in which the number of broken wires probably exceeds value of the discard criteria.

During the rope NDT procedure performed in-situ, audio-alarm and "Zoom Replay" capabilities are useful. The Defectograph generates the audio-signal when the pulse value in the "localised losses" channel has exceeded pre-set alarm level. When a significant rope defect has been observed during recording, the user can stop the rope (or head) movement and recording of signalss, and then may replay a previous recording in the zoom mode. Defect position may be read out precisely and found in the rope. Visual examination of the rope sector in question should then be made, additionally.

Charlie Chong/ Fion Zhang

Solid state memory is an option. This is a credit card size SRAM IC Memory Card conforming to the PCMCIA (PC Card) standard. PCMCIA cards are compatible with almost notebook computers. Also PCMCIA slots can be added to most of personal computer systems. In certain rope NDT conditions, for instance subject to magnetism, this method of data transfer has many advantages. With this option, the Defectograph may store additionally an allrope test record in the memory card. Capacity of the recording depends on the card version, e.g. 1 MB card can storage test of a rope of 600 m in length and 4 MB - 2400 m. Then data may be sent easily and quickly to a computer via the PCMCIA slot. This way, the user can archive many test records for further comparative analysis and can employ software to help him in his work on rope test results. Also data from Memory Card may be replayed on a strip chart with an MD120 Defectograph, including old test records from computer storage memory.

Charlie Chong/ Fion Zhang

The recorder prints automatically the number of annotations on strip chart, e.g. rope length in metres, a rope code set by the operator; recorder settings, direction of movement, date and time. Before a rope test, the user can enter into the instrument a specific identification code, which will be printed on the chart, and test settings like channel sensitivities will be stored with this identification code in non-volatile memory in the instrument. If the same codes are entered in future, the same settings may be applied automatically.

Charlie Chong/ Fion Zhang

The recorder may operate in one of two main modes: chart feed synchronous to rope movement; or chart feed at constant selectable speed. Recording is done by means of a thermal array line printing on thermal paper. All of the instrument settings and measured values are displayed on a liquid crystal display. Any instrument setting may be changed with one only knob-pushbutton.

The instrument is designed for field service. Built in aluminium covered case with handle, the MD120 Defectograph is easy to carry. MD120 operates from a built-in rechargeable battery or various external power sources, AC or DC. Automatically microprocessor controlled recharging while external power is connected is provided.

Field service and user-friendly oriented functionality of the MD120 in conjunction with its capability of computer aided post-testing analysis make this instrument useful as well as every-day tool for rope expert and as a source of data for researchers and developers of methods. Easy access to the test records with computer software tools seems to be a real aid to make faster progress in the development of rope evaluation methods.

Charlie Chong/ Fion Zhang

End of Reading I

Charlie Chong/ Fion Zhang

Reading 2: E1571-01 Standard Practice for Electromagnetic Examination of Ferromagnetic Steel Wire Rope

Charlie Chong/ Fion Zhang

Designation: E1571-01

1. Scope 1.1 This practice covers the application and standardization of instruments that use the electromagnetic, the magnetic flux, and the magnetic flux leakage examination method to detect flaws and changes in metallic crossectional areas in ferromagnetic wire rope products.

1.1.1 This practice includes rope diameters up to 2.5 in. (63.5 mm). Larger diameters may be included, subject to agreement by the users of this practice.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Keywords: to detect (1) flaws and (2) changes in metallic cross- sectional areas in ferromagnetic wire rope products.

Charlie Chong/ Fion Zhang

2. Referenced Documents 2.1 ASTM Standards: E 543 Practice for Agencies Performing Nondestructive Testing2 E 1316 Terminology for Nondestructive Examinations

Charlie Chong/ Fion Zhang

3. Terminology 3.1 Definitionsâ&#x20AC;&#x201D;See Terminology E 1316 for general terminology applicable to this practice.

3.2 Definitions of Terms Specific to This Standard: 3.2.1 dual- Indunction instrumentâ&#x20AC;&#x201D;a wire rope NDT instrument designed to detect and display changes of metallic cross-sectional area on one channel and local flaws on another channel of a dual-channel strip chart recorder or another appropriate device.

3.2.2 local flaw (LF)â&#x20AC;&#x201D;a discontinuity in a rope, such as a broken or damaged wire, a corrosion pit on a wire, a groove worn into a wire, or any other physical condition that degrades the integrity of the rope in a localized manner.

Charlie Chong/ Fion Zhang

3.2.3 loss of metallic cross-sectional area (LMA)â&#x20AC;&#x201D;a relative measure of the amount of material (mass) missing from a location along the wire rope and is measured by comparing a point with a reference point on the rope that represents maximum metallic cross-sectional area, as measured with an instrument.

3.2.4 single-function instrumentâ&#x20AC;&#x201D;a wire rope NDT instrument designed to detect and display either changes in metallic cross-sectional area or local flaws, but not both, on a strip chart recorder or another appropriate device.

Charlie Chong/ Fion Zhang

4. Summary of Practice 4.1 The principle of operation of a wire rope nondestructive examination instrument is as follows: 4.1.1 AC Electromagnetic Instrument - An electromagnetic wire rope examination instrument works on the transformer principle with primary and secondary coils wound around the rope (Fig. 1). The rope acts as the transformer core. The primary (exciter) coil is energized with a low frequency alternating current (ac), typically in the 10 to 30 Hz range. The secondary (search) coil measures the magnetic characteristics of the rope. Any significant change in the magnetic characteristics in the core (wire rope) will be reflected as voltage changes (amplitude and phase) in the secondary coil.

Electromagnetic instruments operate at relatively low magnetic field strengths; therefore, it is necessary to completely demagnetize the rope before the start of an examination. This type of instrument is designed to detect changes in metallic crosssectional area. (LMA only?)

Keywords: AC Electromagnetic Instrument

Charlie Chong/ Fion Zhang

FIG. 1 Schematic Representation of an Electromagnetic Instrument SensorHead

Charlie Chong/ Fion Zhang

4.1.2 Direct Current and Permanent Magnet (Magnetic Flux) Instrumentsâ&#x20AC;&#x201D; irect current (dc) and permanent magnet instruments (Figs. 2 and 3) supply a constant flux that magnetizes a length of rope as it passes through the sensor head (magnetizing circuit). The total axial magnetic flux in the rope can be measured either by Hall effect sensors, an encircling (sense) coil, or by any other appropriate device that can measure absolute magnetic fields or variations in a steady magnetic field. The signal from the sensors is electronically processed, and the output voltage is proportional to the volume of steel or the change in metallic cross-sectional area, within the region of influence of the magnetizing circuit. This type of instrument measures changes in metallic cross-sectional area. (LMA only as either â&#x2C6;&#x2020;A or A)

Charlie Chong/ Fion Zhang

FIG. 2 Schematic Representation of a Permanent Magnet Equipped Sensoread Using a Sense Coil to Measure the Loss of Metallic Cross-Sectional Area

Charlie Chong/ Fion Zhang

FIG. 3 Schematic Representation of a Permanent Magnet Equipped Sensoread Using Hall Devices to Measure the Loss of Metallic Cross-Sectional Area

Charlie Chong/ Fion Zhang

4.1.3 Magnetic Flux Leakage Instrument—A direct current or permanent magnet instrument (Fig. 4) is used to supply a constant flux that magnetizes a length of rope as it passes through the sensor head (magnetizing circuit). The magnetic flux leakage created by a discontinuity in the rope, such as a broken wire, can be detected with a differential sensor, such as a Hall effect sensor, sensor coils, or by any appropriate device. The signal from the sensor is electronically processed and recorded.

This type of instrument measures LFs. While the information is not quantitative as to the exact nature and magnitude of the causal 前因后果的 flaws, valuable conclusions can be drawn as to the presence of broken wires, internal corrosion, and fretting of wires in the rope.”

Charlie Chong/ Fion Zhang

FIG. 4 Illustration of the Leakage Flux Produced by a Broken Wire

Charlie Chong/ Fion Zhang

FIG. 4 Illustration of the Leakage Flux Produced by a Broken Wire

Charlie Chong/ Fion Zhang

4.2 The examination is conducted using one or more techniques discussed in 4.1. Loss of metallic cross-sectional area (LMA) can be determined by using an instrument operating according to the principle discussed in 4.1.1 and 4.1.2. Broken wires and internal (or external) corrosion (LF) can be detected by using a magnetic flux leakage instrument as described in 4.1.3.

The examination procedure must conform to Section 9. One instrument may incorporate both magnetic flux and magnetic flux leakage principles.

Keywords: (1) magnetic flux and (2) magnetic flux leakage principles.

Charlie Chong/ Fion Zhang

5. Significance and Use 5.1 This practice outlines a procedure to standardize an instrument and to use the instrument to examine ferromagnetic wire rope products in which the electromagnetic, magnetic flux, magnetic flux leakage, or any combination of these methods is used. If properly applied, the electromagnetic and the magnetic flux methods are capable of detecting the presence, location, and magnitude of metal loss from wear and corrosion, and the magnetic flux leakage method is capable of detecting the presence and location of flaws such as broken wires and corrosion pits.

5.2 The instrumentâ&#x20AC;&#x2122;s response to the ropeâ&#x20AC;&#x2122;s fabrication, installation, and inervice-induced flaws can be significantly different from the instrumentâ&#x20AC;&#x2122;s response to artificial flaws such as wire gaps or added wires. For this reason, it is preferable to detect and mark (using set-up standards that represent) real in-service-induced flaws whose characteristics will adversely affect the serviceability of the wire rope.

Charlie Chong/ Fion Zhang

6. Basis of Application 6.1 The following items require agreement by the users of this practice and should be included in the rope examination contract: 6.1.1 Acceptance criteria.

6.1.2 Determination of LMA, or the display of LFs, or both.

6.1.3 Extent of rope examination (that is, full length that may require several setups or partial length with one setup).

6.1.4 Standardization method to be used: wire rope reference standard, rod reference standards, or a combination thereof.

6.1.5 Maximum time interval between equipment standardizations.

Charlie Chong/ Fion Zhang

6.2 Wire Rope Reference Standard (Fig. 5): 6.2.1 Type, dimension, location, and number of artificial anomalies to be placed on a wire rope reference standard.

6.2.2 Methods of verifying dimensions of artificial anomalies placed on a wire rope reference standard and allowable tolerances.

6.2.3 Diameter and construction of wire rope(s) used for a wire rope reference standard.

Charlie Chong/ Fion Zhang

FIG. 5 Example of a Wire Rope Reference Standard

Charlie Chong/ Fion Zhang

6.3 Rod Reference Standards (Fig. 6): 6.3.1 Rod reference standard use, whether in the laboratory or in the field, or both.

6.3.2 Quantity, lengths, and diameters of rod reference standards.

Charlie Chong/ Fion Zhang

FIG. 6 Example of a Rod Reference Standard

Charlie Chong/ Fion Zhang

7. Limitations 7.1 General Limitations: 7.1.1 This practice is limited to the examination of ferromagnetic steel ropes.

7.1.2 It is difficult, if not impossible, to detect flaws at or near rope terminations and ferromagnetic steel connections.

7.1.3 Deterioration of a purely metallurgical nature (brittleness, fatigue, etc.) may not be easily distinguishable.

7.1.4 A given size sensor head accommodates a limited range of rope diameters, the combination (between rope outside diameter and sensor head inside diameter) of which provides an acceptable minimum air gap to assure a reliable examination.

Charlie Chong/ Fion Zhang

7.2 Limitations Inherent in the Use of Electromagnetic and Magnetic Flux Methods: 7.2.1 Instruments designed to measure changes in metallic cross-sectional area are capable of showing changes relative to that point on the rope where the instrument was standardized.

7.2.2 The sensitivity of these methods may decrease with the depth of the flaw from the surface of the rope and with decreasing gaps between the ends of the broken wires.

Charlie Chong/ Fion Zhang

7.3 Limitations Inherent in the Use of the Magnetic Flux Leakage Method: 7.3.1 It may be impossible to discern relatively small diameter broken wires, broken wires with small gaps, or individual broken wires within closely-spaced multiple breaks. It may be impossible to discern broken wires from wires with corrosion pits.

7.3.2 Because deterioration of a purely metallurgical nature may not be easily distinguishable, more frequent examinations may be necessary after broken wires are detected to determine when the rope should be retired, based on percent rate of increase of broken wires.

Charlie Chong/ Fion Zhang

8. Apparatus 8.1 The equipment used shall be specifically designed to examine ferromagnetic wire rope products.

8.1.1 The energizing unit within the sensor head shall consist of permanent or electromagnets, or ac or dc solenoid coils configured to allow application to the rope at the location of service.

8.1.2 The energizing unit, excluding the ac solenoid coil, shall be capable of magnetically saturating the range (size and construction) of ropes for which it was designed.

8.1.3 The sensor head, containing the energizing and detecting units, and other components, should be designed to accommodate different rope diameters. The rope should be approximately centered in the sensor head.

Charlie Chong/ Fion Zhang

8.1.4 The instrument should have connectors, or other means, for transmitting output signals to strip chart recorders, data recorders, or a multifunction computer interface. The instrument may also contain meters, bar indicators, or other display devices, necessary for instrument setup, standardization, and examination.

8.1.5 The instrument should have an examination distance and rope speed output indicating the current examination distance traveled and rope speed or, whenever applicable, have a proportional drive chart control that synchronizes the chart speed with the rope speed.

8.2 Auxiliary Equipment The examination results shall be recorded on a permanent basis by either 8.2.1 a strip chart recorder 8.2.2 and/or by an other type of data recorder 8.2.3 and/or by a multifunctional computer interface.

Charlie Chong/ Fion Zhang

9. Examination Procedure 9.1 The electronic system shall have a pre-examination standardization procedure.

9.2 The wire rope shall be examined for LFs or LMA, or both, as specified in the agreement by the users of this practice. The users may select the instrument that best suits the intended purpose of the examination. The examination should be conducted as follows: 9.2.1 The rope must be demagnetized before examination by an electromagnetic instrument. If a magnetic flux or a magnetic flux leakage instrument is used, it may be necessary to repeat the examination to homogenize the magnetization of the rope.

Charlie Chong/ Fion Zhang

9.2.2 The sensor head must be approximately centered around the wire rope.

9.2.3 The instrument must be adjusted in accordance with a procedure. The sensitivity setting should be verified prior to starting the examination by inserting a ferromagnetic steel rod or wire of known cross-sectional area. This standardization signal should be permanently recorded for future reference.

9.2.4 The wire rope must be examined by moving the head, or the rope, at a relatively uniform speed. Relevant signal(s) must be recorded on suitable media, such as on a strip chart recorder, on a tape recorder, or on computer file(s), for the purpose of both present and future replay/analysis.

Charlie Chong/ Fion Zhang

9.2.5 The following information shall be recorded as examination data for analysis: 9.2.5.1 Date of examination, 9.2.5.2 Examination number, 9.2.5.3 Customer identification, 9.2.5.4 Rope identification (use, location, reel and ropenumber, etc.), 9.2.5.5 Rope diameter and construction, 9.2.5.6 Instrument serial number, 9.2.5.7 Instrument standardization settings, 9.2.5.8 Strip chart recorder settings, 9.2.5.9 Strip chart speed, 9.2.5.10 Location of sensor head with respect to a welldefined reference point along the rope, both at the beginning ofthe examination and when commencing a second set-up run, 9.2.5.11 Direction of rope or sensor head travel, 9.2.5.12 Total length of rope examined, and 9.2.5.13 examination speed.

Charlie Chong/ Fion Zhang

9.2.6 To assure repeatability of the examination results, two or more operational passes are required.

9.2.7 When more than one setup is required to examine the full working length of the rope, the sensor head should be positioned to maintain the same magnetic polarity with respect to the rope for all setups. For strip chart alignment purposes, a temporary marker should be placed on the rope at a point common to the two adjacent runs. (A ferromagnetic marker shows an indication on a recording device.) The same instrument detection signals should be achieved for the same standard when future examinations are conducted on the same rope.

Charlie Chong/ Fion Zhang

9.2.8 When determining percent LMA, it must be understood that comparisons are made with respect to a reference point on the rope representing maximum metallic crosssectional area. The reference point may have deteriorated such that it does not represent the original (new) rope. The reference point must be inspected visually to evaluate its condition. When determining percent LMA, it must be understood that comparisons are made with respect to a reference point on the rope that represents the ropeâ&#x20AC;&#x2122;s maximum metallic crosssectional area. The reference pointâ&#x20AC;&#x2122;s condition may have deteriorated during the ropeâ&#x20AC;&#x2122;s operational use such that it no longer represents the original (new) rope values. The reference point must be examined visually, and possibly by other means, to evaluate its current condition.

Charlie Chong/ Fion Zhang

9.2.9 If the NDT indicates existence of significant rope deterioration at any rope location, an additional NDT of this location(s) should be conducted to check for indication repeatability. Rope locations at which the NDT indicates significant deterioration must be examined visually in addition to the NDT. 9.3 Local flaw baseline data for LF and LMA/LF instruments may be established during the initial examination of a (new) rope. Whenever applicable, gain settings for future examination of the same rope should be adjusted to produce the same amplitude for a known flaw, such as a rod or wire attached to the rope.

Charlie Chong/ Fion Zhang

10. Reference Standard 10.1 General: 10.1.1 The instrument should be standardized with respect to the acceptance criteria established by the users of this practice.

10.1.2 Standardization should be done the first time the instrument is used, during periodic checks, or in the event of a suspected malfunction.

10.1.3 The instrument should be standardized using one or more of the following: wire rope reference standard with artificial flaws (see Fig. 5), or rod reference standards (see Fig. 6).

For clarification, the following sections â&#x20AC;&#x201C; 10.2 and 10.3 â&#x20AC;&#x201C; are useful for laboratory purposes to more fully understand instrument limitations.

Charlie Chong/ Fion Zhang

10.2 Wire Rope Reference Standard: 10.2.1 The wire ropes selected for reference standards should be first examined to ascertain and account for the existence of interfering, preexisting flaws (if they exist) prior to the introduction of artificial flaws. The reference standard shall be that rope appropriate for the instrument and sensor head being used and for the wire rope to be examined unless rod reference standards are used. The reference standard shall be of sufficient length to permit the required spacing of artificial flaws and to provide sufficient space to avoid rope end effects. The selected configuration for the reference standard rope shall be as established by the users of this practice.

Charlie Chong/ Fion Zhang

10.2.2 Artificial flaws placed in the wire rope reference standard shall include gaps produced by removing, or by adding, lengths of outer wire.

The gaps shall have typical lengths of 1⁄16 , 1⁄8 , 1⁄4 , 1⁄2 , 1, 2, 4, 8, 16, and 32 in. (1.6, 3.2, 6.4, 12.7, 25.4, 50.8, 101.6, 203.2, 406.4, and 812.8 mm, respectively). (?)

The gaps shall typically be spaced 30 in. (762 mm) apart. There shall be a minimum of 48 in. (1219 mm) between gaps and the ends of the wire rope.

Some of the gap lengths may not be required. All wire ends shall be square and perpendicular to the wire.

10.2.3 Stricter requirements than those stated above for local flaws and changes in metallic cross-sectional area may be established by the users if proven feasible for a given NDT instrument, subject to agreement by the users.

Charlie Chong/ Fion Zhang

10.3 Rod Reference Standard: 10.3.1 Steel rods are assembled in a manner such that the total crossectional area will be equal to the cross-sectional area of the wire rope to be examined. The rod bundle is to be placed in the sensor head in a manner simulating the conditions that arise when a rope is placed along the axis of the examination head. Individual rods are to be removed to simulate loss of metallic area caused by wear, corrosion, or missing wires in a rope. This procedure gives highly accurate control of changes in instrument response and can be used to adjust and standardize the instrument.

10.3.2 The rods for laboratory standardization procedures should be a minimum of 3 ft (Approx. 1 m) in length to minimize end-effects from the rod ends, or as recommended by the instrument manufacturer.

10.3.3 Shorter rods or wires may be used for a preexamination check in the field.

Charlie Chong/ Fion Zhang

10.4 Adjustment and Standardization of Apparatus Sensitivity: 10.4.1 The procedure for setting up and checking the sensitivity of the apparatus is as follows: 10.4.1.1 The reference standard shall be fabricated as specified in the agreement by the users.

10.4.1.2 The sensor head shall be adjusted for the size of material to be examined.

10.4.1.3 The sensor head shall be installed around the reference standard.

10.4.1.4 The reference standard shall be scanned, and, whenever applicable, gain and zero potentiometers, chart recording scale, or other apparatus controls shall be adjusted for required performance.

Charlie Chong/ Fion Zhang

10.4.1.5 If standardization is a static procedure, as with an electromagnetic instrument (see 4.1.1), the standard reference rope shall be passed through the detector assembly at field examination speed to demonstrate adequate dynamic performance of the examination instrument. The instrument settings that provide required standardization shall be recorded.

Charlie Chong/ Fion Zhang

11. Test Agency Qualification 11.1 Nondestructive Testing Agency Qualificationâ&#x20AC;&#x201D;Use of an NDT agency (in accordance with Practice E 543) to perform the examination may be agreed upon by the using parties. If a systematic assessment of the capability of the agency is specified, a documented procedure such as Practice E 543 shall be used as the basis for the assessment.

12. Keywords 12.1 electromagnetic examination; flux leakage; local flaws (LF); Magnetic flux; magnetic flux leakage; percent loss of metallic cross-sectional area (LMA); rod reference standards; sensor head; wire rope; wire rope reference standard

Charlie Chong/ Fion Zhang

End of Reading II

Charlie Chong/ Fion Zhang

Remote Field Testing

Charlie Chong/ Fion Zhang

Remote Field Testing Level I Q&A

Charlie Chong/ Fion Zhang

1. RFT means: a. Random Field Transition b. Reluctance Field Testing c. Remote Field Testing d. Remote Fitness Testing B.3.2.5 2. According to ASTM Standard Practice E 2096-00, the definition of remote field is: a. electromagnetic testing done at remote locations b. the electromagnetic field which has been transmitted through the test object and is observable beyond the direct coupling zone of the exciter c. through-transmission eddy currents, detected on the far side of a material or object under test by a remote receiver coil d. the opposite of direct field B.3.2.4

Charlie Chong/ Fion Zhang

3. The dominant electromagnetic energy distribution process in RFT is said to be: a. reflected impedance b. through-transmission c. piezoelectric energy conversion d. magneto-motive force D.969,970 4. Eddy currents are induced in any material that is subjected to a. conductive/a constant magnetic field b. insulating/a constant electric field c. conductive/a time-varying magnetic field I.51

Charlie Chong/ Fion Zhang

5. In a properly designed RFT probe, the detector coil is positioned in the: a. direct field zone b. transition zone c. remote field zone d. junction between the remote field zone and the transition zone D.969 6. RFT tube standards: a. must include a permeability variation b. are preferably of the same material, diameter and thickness as the tubes to be examined c. should have internal and external wall loss reference discontinuities d. are always made of SA178 carbon steel B.10.1

Charlie Chong/ Fion Zhang

7. Frequencies selected for RFT inspections are: a. usually higher than those used in conventional eddy current tests b. usually lower than those used in conventional eddy current tests c. in the same range as those used in conventional eddy current tests d. carefully calculated and must never be changed during an inspection C.226

Charlie Chong/ Fion Zhang

8. Compared to a conventional eddy current probe, a typical RFT probe: a. has a larger inter-coil spacing b. requires more protection from vibration c. generates greater adhesion forces to the tube wall d. requires a greater fill factor D.969

Charlie Chong/ Fion Zhang

9. Reducing the exciter-to-detector coil spacing in an RFT probe will: a. move the detector into the transition zone or direct-coupling zone b. improve detectability of gradual discontinuities c. increase the signal-to-noise ratio d. allow faster tube inspection speed D.969-971(Fig. 3) 10. A standard bobbin coil eddy current inspection used to inspect carbon steel tubes will: a. reliably detect internal and external discontinuities b. usually fail to reliably detect external discontinuities c. have a very good SIN ratio d. make tube support signals very large C.227

Charlie Chong/ Fion Zhang

11. The terminology used to describe the time delay of a received RFT signal with reference to the exciter signal is called: a. magnitude b. impedance c. phase, phase-shift, phase-lag or phase rotation d. amplitude or log-amplitude A.80 12. As the field produced by an RFT coil passes through the tube wall, it experiences: a. amplification b. attenuation c. flux leakage d. phase increase 0.969

Charlie Chong/ Fion Zhang

13. Eddy current testing is a ____technique while RFT is a ___technique. a. rotation/amplitude b. reflection/through-transmission c. reflection/refraction d. pulse-echo/through-transmission D.969 14. Eddy current testing and RFT are both: a. reflection techniques b. refraction techniques c. through-transmission techniques d. electromagnetic techniques I.46

Charlie Chong/ Fion Zhang

15. The term "phase measurement" can mean: a. phase-shift b. phase angle c. phase-lag d. all of the above A.80 16. The skin depth (depth of penetration of the magnetic field into the tube wall where the field has been attenuated to 37% of its initial amplitude) is dependent upon: a. inspection frequency, phase and tube conductivity b. the phase-lag measured at the detector coil c. inspection frequency, tube permeability and tube conductivity d. coefficient of conductivity for the tube A.80-81

Charlie Chong/ Fion Zhang

17. Ferromagnetic materials: a. have a relative permeability much less than 1 b. include brass, titanium and copper c. are attracted to permanent magnets d. tend to attenuate a through transmission field less than nonferromagnetic materials I.481 18. Increasing the RFT operating frequency: a. allows examination of tubing with greater wall thickness b. always reduces the noise level c. can give better sensitivity to small discontinuities d. increases the thickness of one standard depth of penetration in the material I.210

Charlie Chong/ Fion Zhang

19. If an RFT probe is pulled rapidly through a tube: a. the job will get done faster b. the data will improve due to less noise c. accuracy will increase d. small volume discontinuities, like pits, could be missed I.215 20. What is the effect of lowering the frequency of an RFT system? a. the detector signal will get smaller b. the probe can be pulled faster c. the probe can be used to inspect thicker materials d. signals from tube support plates will get smaller 1.214

Charlie Chong/ Fion Zhang

Recalling the mistakes

Charlie Chong/ Fion Zhang

Remote Field Testing Level II Q&A

O TW

Charlie Chong/ Fion Zhang

1. One method that may help improve signal-to-noise ratio is to: a. increase the drive voltage to the exciter b. adjust the strip chart display settings c. pull the probe through the tubes faster d. select a probe with a fill-factor less than 0.5 C.225 2. A simple RFT probe has one exciter and one detector coil. A long circumferential discontinuity covering both coils gives a phase shift of 100° on the RFT voltage plane. The probe is moved so that only one coil is in the discontinuity. The phase shift will now be: a. 25° b. 50° c. 100° d. 200° C.226

Charlie Chong/ Fion Zhang

3. The two signal components that are indicators of overall wall thickness loss are: a. sample rate and signal amplitude b. phase and amplitude c. signal strength and coil impedance d. the frequency and noise level of the signal B.9.4.2 4. With basic exciter-detector RFT probes, short volumetric discontinuities usually create: a. a near-zero signal b. a double peak in strip chart data c. a decrease in conductivity d. an indication that is seen by the exciter and the detector simultaneously 1.221

Charlie Chong/ Fion Zhang

5. An effective approach to characterize discontinuities is to: a. compare both phase and amplitude information b. note amplitude deflections alone (because phase is less reliable) c. identify regions where the signal-to-noise level is low d. use all X-Y deflections larger than 1.0 V that are between 0째 and 40째 I.220 6. One-sided metal loss: a. creates indications that extend towards the zero-signal point b. creates indications similar to wall thickening c. is created by instrument noise d. creates a phase deflection greater than a log-amplitude deflection I.221

Charlie Chong/ Fion Zhang

7. Baffle plates or support plates: a. are usually nonconducting and nonferromagnetic and do not affect the RFT signal b. have an indication very similar to metal loss c. cause a deflection in the amplitude trace in the metal loss direction d. reduce the through-transmission process dramatically 1.222

Charlie Chong/ Fion Zhang

8. A discontinuity indication that lies along the reference spiral on the voltage plane is usually: a. one sided b. pitting c. permeability variation d. uniform wall loss I.221-222 9. When performing an RFT exam using a RFT voltage plane display, the nominal point is positioned at X-Y coordinates: a. (1,0) b. (0, 1) c. the air point, rotated to lie on the negative Y axis d. where the reference curve meets 0,0 G.4/1.217-218(Fig. 19),220

Charlie Chong/ Fion Zhang

10. Given the following choices, a reasonable RFT probe pull speed is about: a. 2.5 cm per second ( 1 in. per second) b. 30.5 cm per second (1 ft per second) c. 200 cm per second ( 6 ft per second) d. 60 cm per second (2ft per second) I.222 11. A voltage plane display would show: a. the phase and amplitude of a signal in polar coordinates b. the frequency and drive voltage along the x and y axes, respectively c. the probe air-signal placed at the origin d. probe lift-off noise along the X axis G.4

Charlie Chong/ Fion Zhang

12. On a voltage plane display, indications from baffle plates: a. tend to extend close to the origin (near-zero signal) b. always follow the reference spiral closely c. do not change in the presence of metal loss d. are rotated by accumulations of nonmagnetic, nonconducting debris 1.219

Charlie Chong/ Fion Zhang

13. The differential channel signal is best for: a. small-volume discontinuity detection like pits and cracks b. long, gradual wall loss, such as steam erosion c. one-sided wall loss like mid-span erosion d. under-TSP discontinuity detection I.219 14. An X-Y output display: a. shows signals that are linearly proportional to wall loss b. can indicate the circumferential extent of discontinuities c. shows the relationship between discontinuity area and depth clearly d. none of the above B.9.4.2

Charlie Chong/ Fion Zhang

15. The length (or height) of the signal on the voltage plane polar plot may be related to: a. the circumferential extent of the discontinuity b. the depth of the discontinuity c. the temperature of the tube material d. either a or b I.220 16. The following discontinuities are likely not detectable with RFT: a. mid-span erosion b. steam impingement erosion c. tubesheet wormholing d. general corrosion I.222

Charlie Chong/ Fion Zhang

17. If the phase and log-amplitude signals are superimposed on the strip chart display: a. they will separate when going over a 360째 discontinuity of constant depth b. they will closely track each other when going over a 360째 discontinuity of constant depth c. they will go in opposite directions when going over a 360째 discontinuity of constant depth F(Fig. 2)

Charlie Chong/ Fion Zhang

18. The circumferential extent can only be displayed accurately with: a. differential signals on an X-Y display b. absolute signals on an X-Y display c. absolute signals on a voltage plane with a ref curve d. MIX signals on an X-Y display I.219-220 19. Eddy current systems can be used effectively to inspect high permeability tubes without magnetic saturation: a. true b. false c. only true if slow pull speeds are used I.215(Table 1)

Charlie Chong/ Fion Zhang

20. RFT systems are highly effective in inspecting thin-wall, type 304 stainless steel tubes: a. true: the low frequency used in RFT is very effective in thin-walled, low conductivity tubes b. false: a higher frequency technique such as eddy current would give better phase separation c. only true if magnetic saturation probes are used I.481 21. When using RFT to inspect boiler tubes: a. the bend areas cannot be inspected b. the bend areas can be inspected if a comparison technique is used to other tubes with similar bends c. the probe must contain magnets to reduce the permeability value F(Fig. 2)

Charlie Chong/ Fion Zhang

22. At a probe pull speed of 20 cm (7.9 in.) per second with the instrument sample rate set to 40 samples per second, the distance between data sampling points will be: a. 800 cm (26.2 ft) b. 80 cm (31.5 in.) c. 2.0 cm (0.8 in.) d. 0.5 cm (0.2 in.)

I.222

Charlie Chong/ Fion Zhang

Recalling the mistakes

Charlie Chong/ Fion Zhang

Reading 3: Standard Practice for In Situ Examination of Ferromagnetic Heat-Exchanger Tubes Using Remote Field Testing

Charlie Chong/ Fion Zhang

Designation: E 2096-05

1. Scope 1.1 This practice describes procedures to be followed during remote field examination of installed ferromagnetic heatexchanger tubing for baseline and service-induced discontinuities.

1.2 This practice is intended for use on ferromagnetic tubes with outside diameters from 0.500 to 2.000 in. [12.70 to 50.80 mm], with wall thicknesses in the range from 0.028 to 0.134 in. [0.71 to 3.40 mm].

1.3 This practice does not establish tube acceptance criteria; The tube acceptance criteria must be specified by the using parties.

1.4 The values stated in either inch-pound units or SI units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other.

Combining values from the two systems may result in nonconformance with the standard.

Charlie Chong/ Fion Zhang

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents 2.1 ASTM Standards: 2 E 543 Practice for Agencies Performing Nondestructive Testing E 1316 Terminology for Nondestructive Examinations 2.2 Other Documents: ASNT SNT-TC-1A Recommended Practice for Nondestructive Testing Personnel Qualification and Certification Can CGSB-48.9712-95 Qualification of Nondestructive Testing Personnel, Natural Resources Canada4

Charlie Chong/ Fion Zhang

3. Terminology 3.1 General—Definitions of terms used in this practice can be found in Terminology E 1316, Section A, “Common NDT Terms,” and Section C, “Electromagnetic Testing.”

3.2 Definitions: 3.2.1 detector, n—one or more coils or elements used to sense or measure magnetic field; also known as a receiver.

3.2.2 exciter, n—a device that generates a time-varying electromagnetic field, usually a coil energized with alternating current (ac); also known as a transmitter.

3.2.3 nominal tube, n—a tube or tube section meeting the tubing manufacturer’s specifications, with relevant properties typical of a tube being examined, used for reference in interpretation and evaluation.

Charlie Chong/ Fion Zhang

3.2.4 remote field, n—as applied to nondestructive testing, the electromagnetic field which has been transmitted through the test object and is observable beyond the direct coupling field of the exciter.

3.2.5 remote field testing, n—a nondestructive test method that measures changes in the remote field to detect and characterize discontinuities.

3.2.6 using parties, n—the supplier (?) and purchaser.

3.2.6.1 Discussion—The party carrying out the examination is referred to as the “supplier,” and the party requesting the examination is referred to as the “purchaser,” as required in Form and Style for ASTM Standards, April 2004.

In common usage outside this practice, these parties are often referred to as the “operator” and “customer,” respectively.

Charlie Chong/ Fion Zhang

3.3 Definitions of Terms Specific to This Standard: 3.3.1 flaw characterization standard, n—a standard used in addition to the RFT system reference standard, with artificial or service-induced flaws, used for flaw characterization.

3.3.2 nominal point, n—a point on the phase- mplitude diagram representing data from nominal tube.

3.3.3 phase-amplitude diagram, n—a two-dimensional representation of detector output voltage, with angle representing phase with respect to a reference signal, and radius representing amplitude (Fig. 1a and 1b).

3.3.3.1 Discussion—In this practice, care has been taken to use the term “phase angle” (and “phase”) to refer to an angular equivalent of time displacement, as defined in Terminology E 1316. When an angle is not necessarily representative of time, the general term “angle of an indication on the phaseamplitude diagram” is used.

Charlie Chong/ Fion Zhang

FIG. 1 A and B: Typical Phase-Amplitude Diagrams Used in RFT; C: Generic Strip Chart With Flaw

Charlie Chong/ Fion Zhang

FIG. 1 A and B: Typical Phase-Amplitude Diagrams Used in RFT; C: Generic Strip Chart With Flaw A

Charlie Chong/ Fion Zhang

FIG. 1 A and B: Typical Phase-Amplitude Diagrams Used in RFT; C: Generic Strip Chart With Flaw B

Charlie Chong/ Fion Zhang

FIG. 1 A and B: Typical Phase-Amplitude Diagrams Used in RFT; C: Generic Strip Chart With Flaw

Charlie Chong/ Fion Zhang

3.3.4 RFT system, nâ&#x20AC;&#x201D;the electronic instrumentation, probes, and all associated components and cables required for performing RFT. 3.3.5 RFT system reference standard, nâ&#x20AC;&#x201D;a reference standard with specified artificial flaws, used to set up and standardize a remote field system and to indicate flaw detection sensitivity.

Compare: 3.3.1 flaw characterization standard, nâ&#x20AC;&#x201D;a standard used in addition to the RFT system reference standard, with artificial or service-induced flaws, used for flaw characterization.

Charlie Chong/ Fion Zhang

3.3.6 sample rate—the rate at which data is digitized for display and recording, in data points per second.

3.3.7 strip chart, n—a diagram that plots coordinates extracted from points on a phase-amplitude diagram versus time or axial position (Fig. 1c).

3.3.8 zero point, n—a point on the phase-amplitude diagram representing zero detector output voltage.

3.3.8.1 Discussion—Data on the phase-amplitude diagram are plotted with respect to the zero point. The zero point is separate from the nominal point unless the detector is configured for zero output in nominal tube. The angle of a flaw indication is measured about the nominal point.

3.4 Acronyms:Acronyms: 3.4.1 RFT, n— Remote field testing

Charlie Chong/ Fion Zhang

3.3.8.1 Discussionâ&#x20AC;&#x201D;Data on the phase-amplitude diagram are plotted with respect to the zero point. The zero point is separate from the nominal point unless the detector is configured for zero output in nominal tube. The angle of a flaw indication is measured about the nominal point.

Keywords: Zero Point Nominal point

Charlie Chong/ Fion Zhang

4. Summary of Practice 4.1 The RFT data is collected by passing a probe through each tube. The electromagnetic field transmitted from the exciter to the detector is affected by discontinuities; by the dimensions and electromagnetic properties of the tube; and by objects in and around the tube that are ferromagnetic or conductive.

System sensitivity is verified using the RFT system reference standard.

System sensitivity and settings are checked and recorded prior to and at regular intervals during the examination. Data and system settings are recorded in a manner that allows archiving and later recall of all data and system settings for each tube. Interpretation and evaluation are carried out using one or more flaw characterization standards. The supplier generates a final report detailing the results of the examination.

Note: Are there 2 separate standards being used? â&#x2013; System sensitivity is verified using the RFT system reference standard. â&#x2013; Interpretation and evaluation are carried out using one or more flaw characterization standards.

Charlie Chong/ Fion Zhang

5. Significance and Use 5.1 The purpose of RFT is to evaluate the condition of the tubing. The evaluation results may be used to assess the likelihood of tube failure during service, a task which is not covered by this practice.

5.2 Principle of Probe Operationâ&#x20AC;&#x201D;In a basic RFT probe, the electromagnetic field emitted by an exciter travels outwards through the tube wall, axially along the outside of tube, and back through the tube wall to a detector (Fig. 2a).

Charlie Chong/ Fion Zhang

RFT

Operationâ&#x20AC;&#x201D;In a basic RFT probe, the electromagnetic field emitted by an exciter travels outwards through the tube wall, axially along the outside of tube, and back through the tube wall to a detector

Charlie Chong/ Fion Zhang

http://www.olympus-ims.com/en/ms-5800-tube-inspection/

FIG. 2 RFT Probes NOTE 1â&#x20AC;&#x201D;Arrows indicate flow of electromagnetic energy from exciter to detector. Energy flow is perpendicular to lines of magnetic flux.

Charlie Chong/ Fion Zhang

FIG. 2 RFT Probes

Charlie Chong/ Fion Zhang

FIG. 2 RFT Probes

Charlie Chong/ Fion Zhang

5.2.1 Flaw indications are created when (1) in thin-walled areas, the field arrives at the detector with less attenuation and less time delay, (2) discontinuities interrupt the lines of magnetic flux, which are aligned mainly axially, or (3) discontinuities interrupt the eddy currents, which flow mainly circumferentially.

A discontinuity at any point on the through transmission path can create a perturbation; thus RFT has approximately equal sensitivity to flaws on the inner and outer walls of the tube.

Charlie Chong/ Fion Zhang

5.2.1 Flaw indications are created when (1) in thin-walled areas, the field arrives at the detector with less attenuation and less time delay, (2) discontinuities interrupt the lines of magnetic flux, which are aligned mainly axially, or (3) discontinuities interrupt the eddy currents, which flow mainly circumferentially.

A discontinuity at any point on the through transmission path can create a perturbation; thus RFT has approximately equal sensitivity to flaws on the inner and outer walls of the tube.

Charlie Chong/ Fion Zhang

5.3 Warning Against Errors in Interpretation.

Characterizing flaws by RFT may involve measuring changes from nominal (or baseline), especially for absolute coil data. The choice of a nominal value is important and often requires judgment. Practitioners should exercise care to use for nominal reference a section of tube that is free of damage (see definition of â&#x20AC;&#x153;nominal tubeâ&#x20AC;? in 3.2.3). In particular, bends used as nominal reference must be free of damage, and tube support plates used as nominal reference should be free of metal loss in the plate and in adjacent tube material. If necessary, a complementary technique (as described in 11.12) may be used to verify the condition of areas used as nominal reference.

Charlie Chong/ Fion Zhang

5.4 Probe Configurationâ&#x20AC;&#x201D;The detector is typically placed two to three tube diameters from the exciter, in a location where the remote field dominates the direct-coupling field. Other probe configurations or designs may be used to optimize flaw detection, as described in 9.3.

5.5 Comparison with Conventional Eddy-Current Testingâ&#x20AC;&#x201D; Conventional eddy-current test coils are typically configured to sense the field from the tube wall in the immediate vicinity of the emitting element, whereas RFT probes are typically designed to detect changes in the remote field.

Charlie Chong/ Fion Zhang

6. Basis of Application 6.1 Personnel Qualification: 6.1.1 Personnel performing examinations to this practice shall be qualified as specified in the contractual agreement.

6.1.2 Recommendations for qualification as an RFT system operator (Level I) are as follows: 6.1.2.1 Forty hours of RFT (Level I) classroom training.

6.1.2.2 Written and practical examinations similar to those described by ASNT SNT-TC-1A or Can CGSB 48.9712-95.

6.1.2.3 Two hundred and fifty hours of field experience under the supervision of a qualified RFT Level II, 50 % of which should involve RFT instrumentation setup and operation.

Charlie Chong/ Fion Zhang

6.1.3 Recommendations for qualification as an RFT data analyst (Level II) are as follows: 6.1.3.1 Forty hours of RFT (Level II) classroom training.

6.1.3.2 Written and practical examinations similar to those described by ASNT SNT-TC-1A or Can CGSB 48.9712-95.

6.1.3.3 Fifteen hundred hours of field experience under the supervision of a qualified RFT Level II or higher, 25 % of which should involve RFT data analysis.

Charlie Chong/ Fion Zhang

NOTE 1—At the time of approval of this practice, no nationally or internationally recognized guideline for personnel qualification in RFT was available.

NOTE 2—Eddy-current training provides some useful background to RFT training. Previous Level II eddy-current certification may count towards 50 % of training and experience hours for RFT Level I, provided that the remaining experience hours are entirely involved in RFT instrumentation setup and operation.

6.2 Qualification of Nondestructive Testing Agencies—If specified in the contractual agreement, NDT agencies shall be qualified and evaluated as described in Practice E 543, with reference to sections on electromagnetic testing. The applicable edition of Practice E 543 shall be specified in the contractual agreement.

Charlie Chong/ Fion Zhang

7. Job Scope and Requirements 7.1 The following items may require agreement between the using parties and should be specified in the purchase document or elsewhere: 7.1.1 Location and type of tube component to be examined, design specifications, degradation history, previous nondestructive examination results, maintenance history, process conditions, and specific types of flaws that are required to be detected, if known.

7.1.2 The maximum window of opportunity for work. (Detection of small flaws may require a slower probe pull speed, which will affect productivity.)

7.1.3 Size, material grade and type, and configuration of tubes to be examined.

7.1.4 A tube numbering or identification system.

Charlie Chong/ Fion Zhang

7.1.5 Extent of examination, for example: complete or partial coverage, which tubes and to what length, whether straight sections only, and the minimum radius of bends that can be examined.

7.1.6 Means of access to tubes, and areas where access may be restricted.

7.1.7 Type of RFT instrument and probe; and description of reference standards used, including such details as dimensions and material.

7.1.8 Required operator qualifications and certification.

7.1.9 Required tube cleanliness.

7.1.10 Environmental conditions, equipment, and preparations that are the responsibility of the purchaser; Common sources of noise that may interfere with the examination.

NOTE 3窶年earby welding activities may be a major source of interference.

Charlie Chong/ Fion Zhang

7.1.11 Complementary methods or techniques (including possible tube removal) that may be used to obtain additional information.

7.1.12 Acceptance criteria to be used in evaluating flaw indications.

7.1.13 Disposition of examination records and reference standards.

7.1.14 Format and outline contents of the examination report.

Charlie Chong/ Fion Zhang

8. Interferences 8.1 This section describes items and conditions which may compromise RFT. 8.2 Material Properties: 8.2.1 Variations in the material properties of ferromagnetic tubes are a otential source of inaccuracy. Impurities, segregation, manufacturing process, grain size, stress history, present stress patterns, temperature history, present temperature, magnetic history, and other factors will affect the electromagnetic response measured during RFT. The conductivity and permeability of tubes with the same grade of material are often measurably different. It is common to find that some of the tubes to be examined are newer tubes with different material properties.

Charlie Chong/ Fion Zhang

8.2.2 Permeability variations may occur at locations where there was uneven temperature or stress during tube manufacture, near welds, at bends, where there were uneven heat transfer conditions during service, at areas where there is cold working (such as that created by an integral finning process), and in other locations. Indications from permeability variations may be mistaken for, or obscure flaw indications. Effects may be less severe in tubes that were stress-relieved during manufacture.

8.2.3 Residual stress, with accompanying permeability variations, may be present when discontinuities are machined into a reference standard, or during the integral finning process.

Charlie Chong/ Fion Zhang

8.2.4 RFT is affected by residual magnetism in the tubing, including residual magnetism created during a previous examination using another magnetic method. Tubes with significant residual magnetism should be demagnetized prior to RFT. 8.3 Ferromagnetic and Conductive Objects: 8.3.1 Objects near the tube that are ferromagnetic or conductive may reduce the sensitivity and accuracy of flaw characterization in their immediate vicinity.

Such objects may in some cases be mistaken for flaws. Knowledge of the mechanical layout of the component to be examined is recommended.

Examples of ferromagnetic or conductive objects include: tube support plates, baffle plates, end plates, tube sheets, anti-vibration bars, neighboring tubes, impingement plates, loose parts, and attachments clamped or welded to a tube.

NOTE 4â&#x20AC;&#x201D;Interference from ferromagnetic or conductive objects can be of practical use when RFT is used to confirm the position of an object installed on a tube or to detect where objects have become detached and have fallen against a tube.

Charlie Chong/ Fion Zhang

8.3.2 Neighboring Tubes: 8.3.2.1 In areas where there is non-constant tube spacing (bowing) or where tubes cross close to each other, there are indications which may be mistaken for flaws.

8.3.2.2 Neighboring or adjacent tubes, in accordance with their number and position, create an offset in the phase. This phenomenon is known as the bundle effect and is a minor source of inaccuracy when absolute readings in nominal tube are required.

8.3.2.3 In cases where multiple RFT probes are used simultaneously in the same heat exchanger, care should be taken to ensure adequate spacing between different probes.

8.3.3 Conductive or magnetic debris in or on a tube that may create false indications or obscure flaw indications should be removed.

Charlie Chong/ Fion Zhang

8.4 Tube Geometry Effects: 8.4.1 Due to geometrical effects (as well as to the effects of permeability variations described in 8.2.2), localized changes in tube diameter such as dents, bulges, expansions, and bends create indications which may obscure or distort flaw indications.

8.4.2 Reductions in the internal diameter may require a smaller diameter probe that is able to pass through the restriction. In the unrestricted sections, flaw sensitivity is likely to be limited by the smaller probe fill factor.

8.4.3 RFT End Effectâ&#x20AC;&#x201D;The field from the exciter is able to propagate around the end of a tube when there is no shielding from a tube sheet or vessel shell.

A flaw indication may be obscured or distorted if the flaw or any active probe element is within approximately three tube diameters of the tube end.

Charlie Chong/ Fion Zhang

8.5 Instrumentation: 8.5.1 The operator should be aware of indicators of noise, saturation, or signal distortion particular to the instrument being used. Special consideration should be given to the following concerns: 8.5.1.1 In a given tube, an RFT system has a frequency where the flaw sensitivity is as high as practical without undue influence from noise.

8.5.1.2 Saturation of electronic components is a potential problem in RFT because signal amplitude increases rapidly with decreasing tube wall thickness. Data acquired under saturation conditions is not acceptable.

8.5.2 Instrument-induced Phase Offsetâ&#x20AC;&#x201D;During the amplification and filtering processes, instruments may introduce a frequency-dependent time delay which appears as a constant phase offset. The instrument phase offset may be a source of error when phase values measured at different frequencies are compared.

Charlie Chong/ Fion Zhang

Key Points:  In a given tube, an RFT system has a frequency where the flaw sensitivity is as high as practical without undue influence from noise.  Saturation of electronic components is a potential problem in RFT because signal amplitude increases rapidly with decreasing tube wall thickness.  Instrument-induced Phase Offset—During the amplification and filtering processes, instruments may introduce a frequency-dependent time delay which appears as a constant phase offset.

Charlie Chong/ Fion Zhang

9. RFT System 9.1 Instrumentationâ&#x20AC;&#x201D;The electronic instrumentation shall be capable of creating exciter signals of one or more frequencies appropriate to the tube material. The apparatus shall be capable of phase and amplitude analysis of detector outputs at each frequency, independent of other frequencies in use simultaneously. The instrument shall display data in real time. The instrument shall be capable of recording data and system settings in a manner that allows archiving and later recall of all data and system settings for each tube.

9.2 Driving Mechanismâ&#x20AC;&#x201D;A mechanical means (manual allows?) of traversing the probe through the tube at approximately constant speed may be used.

Charlie Chong/ Fion Zhang

9.3 Probesâ&#x20AC;&#x201D;The probes should be of the largest diameter practical for the tubes being examined, leaving clearance for debris, dents, changes in tube diameter, and other obstructions. The probes should be of an appropriate configuration and size for the tube being examined and for the flaw type or types to be detected. Probe centering is recommended.

9.3.1 Absolute Detectorsâ&#x20AC;&#x201D;Absolute detectors (Fig. 2c) are commonly used to characterize and locate large-volume and gradual metal loss.

9.3.2 Differential Detectorsâ&#x20AC;&#x201D;Differential detectors (Fig. 2c) tend to maximize the response from small volume flaws and abrupt changes along the tube length, and are also commonly used to locate and characterize large-volume and gradual metal loss.

Charlie Chong/ Fion Zhang

9.3.3 Array Detector—Array detectors use a configuration of multiple sensing elements (Fig. 2c). Each element is sensitive to a discrete section of the tube circumference. The elements may be oriented with their axes aligned axially or radially with respect to the tube.

NOTE 5—The detector’s response represents an average of responses to all flaws within its sensing area.

Charlie Chong/ Fion Zhang

9.3.4 Exciter and Detector Configurationsâ&#x20AC;&#x201D;Probes may have multiple exciters and detectors in a variety of configurations (see, for example, Fig. 2b).

These configurations may reduce interference from support plates and other conductive objects.

Charlie Chong/ Fion Zhang

9.4 Data Displays: 9.4.1 The data display should include a phase-amplitude diagram (Fig. 1a and 1b).

9.4.2 Strip Chartsâ&#x20AC;&#x201D;Coordinates that may be displayed on strip charts include: horizontal position, vertical position, angular position, or radial position.

Angular position may represent phase. Angular position and the logarithm of radial position for an absolute detector may be linearly related to overall wall thickness.

1a

Charlie Chong/ Fion Zhang

1b

10. RFT Tube Standards 10.1 The RFT tube standards should be of the same nominal dimensions, material type, and grade as the tubes to be examined. In the case where a tube standard identical to the tubes to be examined is not available, a demonstration of examination equivalency is recommended. Subsection 11.6.2 specifies how to determine if a reference tube of different properties is appropriate for use.

10.2 The RFT system reference standard shall not be used for flaw characterization unless the artificial flaws can be demonstrated to be similar to the flaws detected.

10.3 Typical Artificial Flaws in Flaw Characterization Standards: 10.3.1 Through, Round-Bottomed, and Flat- ottomed Holesâ&#x20AC;&#x201D;Holes of different depths are used for pit characterization, and may be machined individually or in groups. Drill and milling tools of different diameters can be used to produce different flaw volumes for a given depth of metal loss (Fig. 3a).

Charlie Chong/ Fion Zhang

FIG. 3 Typical Artificial Discontinuities Used for Flaw Characterization Reference Standards NOTE 1窶年ot to scale.

Charlie Chong/ Fion Zhang

FIG. 3 Typical Artificial Discontinuities Used for Flaw Characterization Reference Standards NOTE 1窶年ot to scale.

Charlie Chong/ Fion Zhang

FIG. 3 Typical Artificial Discontinuities Used for Flaw Characterization Reference Standards NOTE 1窶年ot to scale.

Charlie Chong/ Fion Zhang

FIG. 3 Typical Artificial Discontinuities Used for Flaw Characterization Reference Standards NOTE 1窶年ot to scale.

Charlie Chong/ Fion Zhang

10.3.2 Circumferential Groovesâ&#x20AC;&#x201D;A circumferential groove is an area of metal loss whose depth at any axial location is uniform around the tube circumference. Short grooves, with a maximum axial length of less than one half a tube diameter, may be used to simulate small-volume metal loss.

Grooves with an axial length of several tube diameters may be used to simulate uniform wall loss (Fig. 3b).

10.3.3 One-Sided Flawsâ&#x20AC;&#x201D;Metal loss is referred to as onesided if it is predominantly on one side of a tube. Outside diameter long, flat flaws typically simulate tube-to-tube wear. Circumferentially tapered one-sided flaws typically simulate tube wear at support plates. Flaws tapered in both axial and circumferential directions typically simulate steam erosion adjacent to the tube support (Fig. 3c).

Charlie Chong/ Fion Zhang

10.4 RFT System Reference Standards—Flaw depths are specified by giving the deepest point of the flaw as a percentage of the measured average wall thickness. Flaw depths shall be measured and accurate to within ± 20 % of the depth specified or 60.003 in. [± 0.08 mm], whichever is smaller. All other flaw dimensions (such as length and diameter) shall be accurate to within ± 0.010 in. [± 0.25 mm] of the dimension specified. Angles shall be accurate to within ± 5°.

10.5 Artificial Flaws for RFT System Reference Standards: 10.5.1 The RFT system reference standard has specific artificial flaws. It is used to set up and standardize a remote field system and to indicate flaw detection sensitivity. Unless otherwise specified by the purchaser, the artificial flaws for the RFT system reference standard are as follows:

Charlie Chong/ Fion Zhang

10.5.1.1 Through-Holeâ&#x20AC;&#x201D;A through-hole (Fig. 4, Flaw A) whose diameter is equal to the tube wall thickness multiplied by a specified factor. For tubes of outside diameter less than 1.000 in. [25.40 mm], the factor is 1. For tubes of outside diameter greater than or equal to 1.000 in., the factor is 1.5.

10.5.1.2 Flat-Milled Flawâ&#x20AC;&#x201D;Aflat-milled flaw (Fig. 4, Flaw B) of a depth of 50 % and axial length one half the tube nominal outside diameter. The flat should be side-milled using a milling tool of a diameter of 0.250 in. [6.35 mm] to create rounded corners.

Charlie Chong/ Fion Zhang

10.5.1.3 Short Circumferential Groove—A short circumferential groove (Fig. 4, Flaw C) of a depth of 20 % and axial length of 0.625 in. [15.88 mm]. Edges shall be angled at 105° as indicated in the insert in Fig. 4.

10.5.1.4 Wear Scar—A simulated wear scar from a tube support plate (Fig. 4, Flaw D), consisting of a circumferentially tapered groove, 40 % deep, extending over 180° of the tube circumference. Axial length measured at the bottom surface of the flaw shall be 0.625 in. [15.88 mm]. Edges shall be angled at 105° as indicated in the insert in Fig. 4.

10.5.1.5 Tapered Flaw—A tapered flaw simulating neartube- support erosion (Fig. 4, Flaw E) consisting of a groove, 60 % deep, tapered circumferentially, and in both directions axially. The steep side of the flaw shall be angled at 65° to the tube axis. The shallow side of the flaw shall be axially tapered so that it extends an axial distance of four tube diameters from the deepest point.

The circumferential extent at the maximum point shall be 90°.

Charlie Chong/ Fion Zhang

10.5.1.6 Long Circumferential Grooveâ&#x20AC;&#x201D;A long circumferential groove (Fig. 4, Flaw F) of a depth of 20 % and recommended axial length of two tube diameters. Length is optional in accordance with application. Edges shall be angled at 105°, as indicated in the insert in Fig. 4.

10.6 Simulated Support Structures: 10.6.1 The RFT tube standards may have simulated support structures to represent heat exchanger bundle conditions.

10.6.2 Support Platesâ&#x20AC;&#x201D;Support plates may be simulated by drilling a single hole through a solid flat plate with a radial clearance on the tube of up to 0.015 in. [0.38 mm]. To prevent the field from propagating around the plate, the minimum distance from the edge of the tube hole to the edge of the plate should be greater than two tube diameters, unless a smaller dimension can be demonstrated to be adequate. For example, the simulated tube support plate for a 1-in. Diameter tube should be at least a 5-in. [127.00-mm] square or a 5-in. diameter circle. The accuracy of the support plate simulation may be increased if the simulated plate is of the same thickness and material as the support plates in the component to be examined.

Charlie Chong/ Fion Zhang

10.7 Manufacture and Care of RFT Tube Standards: 10.7.1 Drawings—For each RFT tube standard, there shall be a drawing that includes the as-built measured flaw dimensions, material type and grade, and the serial number of the actual RFT tube standard.

10.7.2 Serial Number—Each RFT tube standard shall be identified with a unique serial number and stored so that it can be obtained and used for reference when required.

10.7.3 Flaw Spacing—Artificial flaws should be positioned axially to avoid overlapping of indications and interference from end effects.

10.7.4 Machining personnel shall use proper machining practices to avoid excessive cold-working, over- eating, and undue stress and permeability variations.

10.7.5 Tubes should be stored and shipped so as to prevent mechanical damage.

Charlie Chong/ Fion Zhang

11. Procedure 11.1 If necessary, clean the inside of the tubes to remove obstructions and heavy ferromagnetic or conductive debris.

11.2 Instrument Settings: 11.2.1 Operating Frequencyâ&#x20AC;&#x201D;Using the appropriate RFT system reference standard, the procedures in 11.2.1.1 or 11.2.1.2 are intended to help the user select an operating frequency. Demonstrably equivalent methods may be used. If the RFT system is not capable of operating at the frequency described by this practice, the supplier shall declare to the purchaser that conditions of reduced sensitivity may exist.

11.2.1.1 Using the RFT system reference standard, and referring to the phase-amplitude diagram, set the frequency to obtain a difference of 50 to 120° between the angles of indication for the reference through-hole (FlawAin Fig. 4) and a 20 % circumferential groove of a axial length of 0.125 in. [3.18 mm] (as permitted for Flaw F in Fig. 4).

Charlie Chong/ Fion Zhang

11.2.1.2 If phase is measured and displayed, set the frequency so that a 20 % circumferential groove with an axial length of two tube diameters (as permitted for Flaw F in Fig. 4) creates a phase shift of between 18 and 22° in the absolute detector output with only the detector coil in the region of metal loss.

11.2.2 Secondary Frequencies—To detect and characterize some damage mechanisms, it may be necessary to use secondary frequencies to provide additional information.

11.2.3 Pull Speed—Determine a pull speed appropriate to the frequency, sample rate, and required sensitivity to flaws.

11.2.4 Set other instrument settings as appropriate to achieve the minimum required sensitivity to flaws.

NOTE 6—Factors which influence sensitivity to flaws include, but are not limited to: operating frequency, instrument noise, instrument filtering, digital sample rate, probe speed, coil configuration, fill factor, probe travel noise, and interferences described in Section 8.

Charlie Chong/ Fion Zhang

11.3 Ensure that the system yields the minimum required sensitivity to all flaws on the RFT system reference standard at the examination pull speed.

For a flaw to be considered detectable, its indication should exceed the ambient noise by a factor of at least 3, unless otherwise specified by the purchaser. An exception may be made when the purchaser requires only a large-volume metal loss examination, in which case, sensitivity should be demonstrated for specified large-volume flaws on the RFT system reference standard.

11.4 Acquire and record data from the RFT system reference standard and flaw characterization standards at the selected examination pull speed.

11.5 Acquire and record data from the tubes to be examined. Maintain as uniform a probe speed as possible throughout the examination to produce repeatable indications.

Charlie Chong/ Fion Zhang

11.5.1 Record data and system settings in a manner that allows archiving and later recall of all data and system settings for each tube. Throughout the examination, data shall be permanently recorded, unless otherwise specified by the purchaser.

11.5.2 For maintaining system consistency throughout the examination, monitor typical RFT responses from support plates and tube ends, or monitor the absolute phase in the nominal tube. If conditions change, appropriate adjustments need to be made in accordance with 11.6.

11.6 Compensation for Material and Dimensional Differences: 11.6.1 To compensate for differences in dimensional and material properties, the system may be re-normalized where appropriate by adjusting frequency or gain, or both. To re-normalize, adjust the settings so that one of the following values remains equal in the reference standard and in a nominal examined tube:

Charlie Chong/ Fion Zhang

11.6.1.1 The amplitude and angular position of a support plate indication on the phase-amplitude diagram, or 11.6.1.2 The angular difference between a support plate indication and the tube-exit indication on the phase-amplitude diagram, or 11.6.1.3 The absolute phase in the nominal tube.

NOTE 7窶認or an alternate method of compensating for differences in dimensional and material properties, see 11.12. 1 1.6.2 The frequencies used in the reference standards and in the tubes to be examined should not differ by more than a factor of two. If the factor exceeds this value, the reference standard should be considered inappropriate and replaced with one that more accurately represents the material to be tested.

11.6.3 After frequency and gain adjustments have been made, apply appropriate compensations to the examination sample rate and pull speed.

Charlie Chong/ Fion Zhang

11.7 Compensation for Ferromagnetic or Conductive Objects: 11.7.1 Techniques that may improve RFT results near interfering ferromagnetic or conductive objects include: 11.7.1.1 Comparison of baseline or previous examination data with the current examination data.

11.7.1.2 Comparison of indications from known objects with and without metal loss. (Obtain a reference indication from a typical object on or near the nominal tube or from a simulated object on a reference standard.)

11.7.1.3 The use of special probe coil configurations.

11.7.1.4 Processing of multiple-frequency signals to suppress irrelevant indications. 11.7.1.5 The use of a complementary method or technique (see 11.12).

Charlie Chong/ Fion Zhang

11.8 System Checkâ&#x20AC;&#x201D;At regular intervals, carry out a system check using the RFT system reference standard to demonstrate system sensitivity and operating parameters to the satisfaction of the purchaser. Carry out a system check prior to starting the examination, after any field compensation adjustments in accordance with 11.6, at the beginning and end of each work shift, when equipment function is in doubt, after a change of personnel, after a change of any essential system components, and overall at a minimum of every four hours. If the flaw responses from the RFT system reference standard have changed substantially, the tubes examined since the last system check shall be reexamined.

Charlie Chong/ Fion Zhang

11.9 Interpret the data (identify indications).

11.10 Note areas of limited sensitivity, using indications from the RFT system reference standard as an indicator of flaw detectability.

11.11 Using a flaw characterization standard, evaluate relevant indications in accordance with acceptance criteria specified by the purchaser.

11.11.1 A common parameter used as a flaw depth indicator is the angle of an indication on the phase- amplitude diagram. Different angle-depth standardization curves may be used in accordance with flaw volume, as indicated by the amplitude of the indication on the phase-amplitude diagram.

11.12 If desired, examine selected areas using an appropriate complementary method or technique to obtain more information, adjusting results where appropriate.

11.13 Compile and present a report to the purchaser.

Charlie Chong/ Fion Zhang

12. Report 12.1 The following items may be included in the examination report. All the following information should be archived, whether or not it is required in the report.

12.1.1 Owner, location, type, and serial number of component examined.

12.1.2 Size, material type and grade, and configuration of tubes examined.

12.1.3 Tube numbering system.

12.1.4 Extent of examination, for example, areas of interest, complete or partial coverage, which tubes, and to what length.

12.1.5 Personnel performing the examination and their qualifications.

Charlie Chong/ Fion Zhang

12.1.6 Models, types, and serial numbers of the components of the RFT system used, including probe and extension length.

12.1.7 For the initial data acquisition from the RFT system reference standard, a complete list of all relevant instrument settings and parameters used, such as operating frequencies, probe drive voltages, gains, types of mixed or processed channels, and probe speed. The list shall enable settings to be referenced to each individual tube examined.

12.1.8 Serial numbers of all of the tube standards used.

12.1.9 Brief outline of all techniques used during the examination.

12.1.10 A list of all heat- xchanger regions or specific tubes where limited sensitivity was obtained. Indicate which flaws on the system reference standard would not have been detectable in those regions. Where possible, indicate factors that may have limited sensitivity.

Charlie Chong/ Fion Zhang

12.1.11 Specific information about techniques and depth reference curves used for sizing each indication.

12.1.12 Acceptance criteria used to evaluate indications. 12.1.13 A list of flaws as specified in the purchasing agreement. 12.1.14 Complementary examination results that influenced interpretation and evaluation.

13. Keywords 13.1 eddy current; electromagnetic testing; Ferromagnetic tube; remote field testing; RFT; tube; tubular products

Charlie Chong/ Fion Zhang

End of Reading III

Charlie Chong/ Fion Zhang

Remote Field Testing Level III Q&A

e e r Th

Charlie Chong/ Fion Zhang

1. The symbol δ stands for: a. relative magnetic permeability b. conductivity c. resistivity d. standard depth of penetration A.78 2. If δ increases, it likely means that: a. frequency has increased b. permeability has decreased c. conductivity has decreased d. either b or c A .80

Charlie Chong/ Fion Zhang

3. The symbol used for relative permeability IS: a. δ b. μ c. σ d. ρ A.78 The symbol used for resistivity is: a. δ b. μ c. σ d. ρ A.78

Charlie Chong/ Fion Zhang

5. Local permeability changes caused by stress in the tube will probably: a. change the operating frequency b. produce a signal to the right of the voltage plane reference curve c. rotate the signals CCW d. have no effect because they are minor in comparison to wall loss signals B.2(Fig. 1A) 6. Narrow grooves next to a TSP (tube support plate) are often called: a. baffle wear b. crevice corrosion c. condensate grooving d. midspan erosion I.221

Charlie Chong/ Fion Zhang

7. RFT gives approximately equal signals (phase and amplitude) for internal and external discontinuities of the same depth and area: a. true b. false D.969

Charlie Chong/ Fion Zhang

8. Through-wall hole signals in RFT will always be set at about 40°: a. true: ASTM Standard Practice E 2096-00 requires the through-hole signal to be at 40° b. b. false: ASTM standard practice allows the hole signal to be set so that there is a 50° to 120° separation between the through-hole signal and the signal from a 20% groove B.11.2.1.1 11.2.1.1 Using the RFT system reference standard, and referring to the phase-amplitude diagram, set the frequency to obtain a difference of 50 to 120° between the angles of indication for the reference through-hole (Flaw A in Fig. 4) and a 20 % circumferential groove of a axial length of 0.125 in.

[3.18 mm] (as permitted for Flaw F in Fig. 4).

Charlie Chong/ Fion Zhang

Designation: E 2096 â&#x20AC;&#x201C; 05

Charlie Chong/ Fion Zhang

9. One standard depth of penetration in any material reduces the strength of an eddy current test or RFT signal to about: a. 57% of the signal strength at the surface b. 37% of the signal strength at the surface c. 19% of the signal strength at the surface d. it does not affect the amplitude; it just delays the phase of the signal A.80

Charlie Chong/ Fion Zhang

10. Phase lag can be described as: a. the speeding up of the eddy current signal is dense solids b. the speed of rotation of the probe c. the time delay of the electromagnetic energy as it moves deeper in a conductive material d. the interaction between signal angle and magnitude I.214 11. How many degrees of phase shift have occurred at the 3δ point? a. 171.9 b. 100.3 c. 57.3 d. 37.4 A.81

Charlie Chong/ Fion Zhang

12. The probe drive current is measured in: a. volts b. ohms c. amps d. gigahertz I.22(Table 6),209 13. A "standard depth of penetration" is sometimes referred to as: a. phase lag at 57% b. 6" c. skin depth d. skin deep A.80

Charlie Chong/ Fion Zhang

14. The terminology that most accurately defines the coupling of the coil's electromagnetic energy into the test material is: a. reflection method b. induction c. standard depth d. reduction C.226 15. Magnetic liues of flux are often measured in units of: a. gauss b. siemens c. resistivity d. conductance I.22,24

Charlie Chong/ Fion Zhang

16. Place the following materials in order based on their conductivity (from highest to lowest): a. steel, aluminum, titanium, copper b. aluminum, copper, titanium, steel c. copper, aluminum, steel, titanium d. titanium, steel, copper, aluminum A.90-94 17. The operating or "nominal referenceâ&#x20AC;&#x153; point of the X-Y display of an absolute detector is referenced as: a. the lower left-hand quadrant b. 0,0 c. 1,0 d. 10,0 1.218

Charlie Chong/ Fion Zhang

18. The RFT technique was first patented by W.R. MacLean in: a. 1985 b. 1972 c. 1963 d. 1951 I.208

19. Detector coils placed in the"transition zone" will: a. produce larger, more reliable differential signals than a coil in the remote zone b. produce unpredictable signals c. produce a saturated signal for all discontinuities due to its proximity to the exciter d. not produce any signal I.213

Charlie Chong/ Fion Zhang

20. Detailed maps of the magnetic flux distribution within the tube wall can be produced with: a. Gauss meters b. RFT detector coils c. FEA (Finite Element Analysis) routines d. magnetographs D.974

Charlie Chong/ Fion Zhang

21. The predominant energy that energizes the detector coils in an RFT probe comes from: a. the eddy currents flowing in the wall next to the detector(s) b. the direct field from the exciter, inside the tube c. the through-transmission field moving from the OD to the ID surface of the tube d. residual magnetic events I.211-214

Charlie Chong/ Fion Zhang

22. The term "phase;' as defined by ASTM E 1316, Section C, is: a. the vector position on an impedance plane b. a time delay expressed in terms of a 360ยบ AC cycle c. the X-Y coordinates of a signal on a voltage plane display d. the vector value from 0,0 on an X-Y impedance plane display A.80

Charlie Chong/ Fion Zhang

23. Tubes that have been examined with a magnetic technique such as MFLT prior to the RFT examination will likely exhibit different discontinuity responses than if no other electromagnetic NDT test was previously used: a. true b. false c. only true if a magnetic saturation eddy current test was used d. only true if the saturation coil was DC (rather than an AC coil) B.8.2.4

Charlie Chong/ Fion Zhang

24. Phase-amplitude diagram can also mean: a. impedance plane display b. voltage plane polar plot c. X-Y display d. any or all of the above B.3.3.3 25. In RFT testing, the sample rate signifies: a. the probe pull speed b. the rate at which data is digitized for display and recording c. the cost of taking a sample of data d. the number of tubes that can be inspected on a shift B.3.3.6

Charlie Chong/ Fion Zhang

26. "Zero point" means: a. the crossing of the X and Y axes on an impedance plane display b. the point on the phase-amplitude diagram representing no signal change c. the position of the probe in the tube where there is zero output voltage d. any or all of the above B.3.3.8 27. The following factors may affect the response of an RFT probe: a. temperature history of the tube being tested b. conductivity variations in the material under test c. permeability changes caused by cold working d. all of the above B.8.2.1-2

Charlie Chong/ Fion Zhang

28. The "nominal point" on the phase amplitude diagram, or voltage plane, is: a. the same as the "null" or "balanceâ&#x20AC;&#x153; point b. the point that represents normal wall thickness of a tube c. any point that nominally represents a reference position d. any measurement with respect to the 0,0 position B.3.3.2

Charlie Chong/ Fion Zhang

29. The proximity of other tubes in a heat exchanger is known as the: a. bundle effect b. proximity effect c. shielding effect d. offset effect B.8.3.2.2 30. RFT end effect is: a. the signal obtained from the last tube to be tested b. a large signal, similar to a TSP signal c. the signal from the end of a tube when there is no tube-sheet to shield the signal d. the signal from a wear scar under a TSP 8.8.4.3

Charlie Chong/ Fion Zhang

31. Instrument-induced phase offset is defined as: a. the overall signal phase, as modified by the circuits in the instrument b. the frequency dependent time delay (which appears as a constant phase offset) due to the amplification and filtering processes in the RFT instrument c. the signal angle, rotated by the operator, using the phase rotator control of the instrument d. the signal seen due to the interference of one channel with another B.8.5.2 32. A simple absolute probe: a. contains two coils wound in opposition b. contains only one detector coil c. can detect small volume discontinuities better than differential probes d. uses an array of self-referencing, pancake detector coils B.9.3.1

Charlie Chong/ Fion Zhang

33. Array probes: a. are used for tubes under 0.375 in. (9.525 mm) diameter b. contain multiple coils that interrogate a small section of the tube wall c. are used in explosive atmospheres where they need to be intrinsically safe d. measure the radial field only B.9.3.3 34. Unless otherwise specified by the purchaser, an RFT test standard shall have the following artificial discontinuity(ies) machined into it as a minimum requirement (as per ASTM E 2096-00): a. a through-wall hole, 0.375 in. (9.525 mm) diameter b. a narrow 20% deep, circumferential groove c. a milled-flat of 50% depth, with an axial length of one half the tube OD d. both b and c B.10.5

Charlie Chong/ Fion Zhang

35. Reference standards should be: a. stored and shipped carefully to prevent mechanical damage b. machined carefully to avoid localized over-heating and cold working c. serialized with a unique number as well as the tube OD, metal type and wall thickness d. all of the above B.10.7 36. An X-Y voltage plane display is being used to perform an RFT exam. If phase is a parameter that is being measured, a good choice of frequency would be one that sets the signal from the 20% short circumferential groove in the reference standard to: a. 90" b. 40째 c. between 18째 and 22째 d. aligned with the X axis B.11.2.1.2

Charlie Chong/ Fion Zhang

37. You are operating an RFT system and notice that discontinuity signals are unpredictable. You suspect that the detector is operating in the transition zone. What can you do to get the detectors operating in the remote field zone? a. increase the frequency b. increase drive voltage to the exciter c. decrease detector gain d. decrease the frequency D.976 38. External and internal fluids, gas, oil or salt water will severely degrade the RFT signal: a. true b. false C.225-230

Charlie Chong/ Fion Zhang

39. Discontinuities located in a secondary tube that is positioned over the primary tube (i.e., the primary tube is wholly within the secondary tube) can be detected with RFT: a. true b. false C.225-230 40. Local discontinuities such as pits will produce signals from an absolute probe: a. of high amplitude with open loops b. of high amplitude with closed loops c. of low amplitude, to the left of the reference curve d. of low amplitude, following the reference curve H.656(Fig. 5)

Charlie Chong/ Fion Zhang

41. RFT may be used on ferrous and nonferrous tubes with approximately equal sensitivity to internal and external discontinuities: a. true b. false c. only true if the impedance technique is used D.976 42. Optimum RFT inspection frequencies will produce: a. ten times the skin depth for one transit of the tube wall thickness b. approximately one skin depth for one transit of the tube wall thickness c. approximately 1/4 the skin depth for one transit of the tube wall thickness d. approximately 1/2 the skin depth for one transit of the tube wall thickness E.80

Charlie Chong/ Fion Zhang

43. Proximity of the probe to the inside surface of the tube (i.e., fill factor): a. has almost zero effect on the reading if phase is being measured b. will substantially affect the amplitude of the signal as fill factor gets smaller c. affects both phase and amplitude equally d. both a and b are true E.85 44. When using the RFT reference curve and an absolute probe, general, tapered wall loss will: a. lie inside the curve b. lie outside the curve c. closely follow the curve d. probably follow the curve for much of the signal H.656(Fig. 5)

Charlie Chong/ Fion Zhang

45. When using the RFT reference curve and an absolute probe, permeability variations will: a. usually fall outside the curve, to the right b. produce equal phase and logamplitude signals c. comprise signals that are inside the curve, approaching the 0,0 point d. comprise multiple signals responding in random directions H.656(Fig. 5) 46. When using the RFT reference curve to size a discontinuity, it is important that the remaining wall at the discontinuity is greater than one skin depth; otherwise: a. the indication may fall outside the curve b. the indication may be reduced in amplitude to the point where it is undetectable c. the depth prediction may be nonlinear d. this is a fallacy, since the phase angle will still represent true remaining wall H.655

Charlie Chong/ Fion Zhang

Recalling the mistakes

Charlie Chong/ Fion Zhang

making Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

Good Luck

Charlie Chong/ Fion Zhang

Good Luck

Charlie Chong/ Fion Zhang

https://www.yumpu.com/en/browse/user/charliechong Charlie Chong/ Fion Zhang