electromagnetic testing q&a 004 part 2 of 2

Charlie Chong/ Fion Zhang

Electromagnetic TestingQuestions & Answers -004 Part 2ACFM,EC&MFL,RF Testing-Book(E) 2009My ASNT Level III Pre-Exam Preparatory My Self Study Notes 5th August 2015


Power Plant Applications


Petrochemical Applications

Greek Alphabet


Charlie Chong/ Fion Zhang http://greekhouseoffonts.com/

Fion Zhang at Shanghai5th August 2015

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IVONA TTS Capable.

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A. Length of the test sampleB. Thickness of the test sampleC. Cross sectional area of the test sample

A. Heat treatment give the metalB. Cold working performed on the metalC. Aging process used on the metalD. HardnessE. Crack & discontinuities

Magnetic(Permeability & Dimensions)

Conductivity


FLT-Flux Leakage Testing


FLT Level I Q&A


Answers to Flux Leakage Testing Level I1.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


1. When using a detector coil, what is the primary condition required in orderto obtain a signal from flux leakage?a. have many turns in the detector coilb. provide an electrical connection between the detector coil and the test partc. movement between the detector coil and the test objectd. shielding the cable which connects the detector coil and the recorderA.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.


2. Which of the following currents is appropriate for magnetization of the testobject when doing flux leakage testing using detector coils?a. alternating currentb. half wave currentc. direct currentd. spinning currentD.7/G.267

Since early 1978, the high-energy alternating field stray flux method hasgained in popularity for testing round ferromagnetic bars from 1 to 4.5 in. Indiameter. With the Rotoflux AC magnetic flux leakage (AC-MFL) technique, arotating head (Figure 3.14) containing the magnetizing yoke and sensitivepickup coils rotates as the bar stock is inspected at traverse speeds of 180 to360 feet per minute (fpm). Figure 3.15 shows the cross section of aferromagnetic bar being exposed to an alternating field between the polepieces. Electromagnetic Testing-Chapter 3 Electromagnetic Testing - Paul E.M Section 3.2


3.2 MAGNETIC FLUX LEAKAGE THEORYWhen 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 magnetizedpiece, the permeability is drastically changed and leakage flux will emanatefrom the discontinuity. By measuring the intensity of this leakage flux, we candetermine 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 thepoles.

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.



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.



Based on what we have learned about magnetic flux leakage, Figure 3.10illustrates that a notch or defect distorts the magnetic lines of flux causingleakage 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 3.11illustrates 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 180° apart with a series of magnetic sensors 90° 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.



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 C

hong/ Fion Zhang

Figure 3.12 Rotating direct current magnetic yoke for establishing circular magnetic flux pattern to detect longitudinal defects—Rotomat method. Courtesy of Institut Dr. Foerster.



Flux leakage sensors have small diameters, some as small as 0.02”, in orderto have adequate sensitivity for detecting short-length or small diameterdefects. Because of their small size, the scanning head may have 16 or moresensors in order to achieve satisfactory throughput speeds. Probes arespringloaded against the tube surface to provide fixed lift-off; they are loweredafter the leading end of the tube is detected and raised just before the laggingtube end is reached. Signals from the probes on the inner and outer surfacesof the tube are transmitted through springs to the electronics unit where theyare filtered and analyzed by a continuous spectrum analyzer. Inside andoutside flaws are automatically marked by different-colored dyes that indicatethe size and type of flaws detected. Transverse flaws are detected by passingthe tube through a ring yoke that produces longitudinal magnetization. In thiscase, the tube surface is surrounded by and scanned with a ring of smallprobes. Signal processing and flaw marking is the same as previouslydescribed.



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

Since early 1978, the high-energy alternating field stray flux method hasgained in popularity for testing round ferromagnetic bars from 1 to 4.5 in. Indiameter. With the Rotoflux AC magnetic flux leakage (AC-MFL) technique, arotating head (Figure 3.14) containing the magnetizing yoke and sensitivepickup coils rotates as the bar stock is inspected at traverse speeds of 180 to360 feet per minute (fpm). Figure 3.15 shows the cross section of aferromagnetic bar being exposed to an alternating field between the polepieces.



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 “x’s”, 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.



Figure 3.13 Direct current electromagnet scans length of rotating tube. Circular flux pattern detects longitudinal defects. Courtesy of Institut Dr. Foerster.



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



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



3. Flux leakage occurs in a ferromagnetic material when a discontinuity nearthe surface causes a disturbance of the magnetic field in the part:a. regardless of what created the magnetic fieldb. only if there is an active magnetizing forcec. only if there is a residual magnetic fieldd. only if the magnetic field is a vector fieldD.7

4. Flux leakage inspection may be used on:a. ferromagnetic and non ferromagnetic materialsb. nonferromagnetic materials onlyc. ferromagnetic materials onlyd. all conductive materialsD.7


5. Transverse magnetization in bar or pipe testing is used for the detection of:a. transverse discontinuitiesb. discontinuities that have a longitudinal componentc. both transverse and longitudinal discontinuitiesd. only holesA.230

6. With flux leakage detection coil systems, the difference between similar OD and ID discontinuities is:a. signal amplitudeb. impedancec. noised. signal width and amplitudeG.305/H.75


7. An energized (magnetizing) coil around the part produces:a. a circular fieldb. a longitudinal fieldc. an intermittent fieldd. a field direction dependent on the type of current applied0.44


8. Using Figure 16, what is the normal (vertical) component of the leakageflux at the middle of the wide discontinuity gap of a surface discontinuity?a. zerob. maximumc. equal to the horizontal componentd. divergente. convergentA.235

Bx


9. Flux leakage techniques can normally be used to test for:a. surface discontinuities onlyb. subsurface discontinuities onlyc. discontinuities at any locationd. surface and near-surface discontinuitiesD.39

6. With flux leakage detection coil systems, the difference between similar OD and ID discontinuities is:a. signal amplitudeb. impedancec. noised. signal width and amplitudeG.305/H.75


3.14 MAGNETIC FLUX LEAKAGE TESTINGThe magnetic flux leakage method is dry, fast, online, and recommended bythe American Petroleum Institute for tubes with small to medium wallthickness. Magnetic flux leakage testing is of great importance for processreliability and quality control assurance in the production of oil field and boilertubes.

Magnetic flux leakage tests help assure the safety of nuclear andconventional power plants, offshore platforms, the oil and gas industries, andchemical and petrochemical plants. DC field magnetization is used over theentire cross section of pipes transversely using Rotomat® and longitudinallyusing Transomat® (Figure 3.35), thereby providing simultaneous testing forinternal and external flaws. With appropriate with state-of-the-art filtering andsignal gating, separate indications are provided for internal and external flaws.When testing with external sensors, internal flaws have lower peak height and longer wavelength.



Level II Q&A16. 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


10. A relative motion between the test piece and a ____ is needed in order todetect leakage flux.a. detector coilb. hall effect elementc. magneto probed. piezoelectric crystalA.157,388


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 forceb. length of the crack is perpendicular to the magnetic lines of forcec. length of the crack is diagonal to the magnetic lines of forced. edges of the crack are polarizedA.48/E.4

12. Magnetic properties of a ferromagnetic material are depicted by the:a. hysteresis loopb. minor loopc. recoil curved. magnetization curvee. permeability curveD.45


13. The line shown in Figure 17 is the:a. residual field lineb. virgin curvec. remagnetization lined. flux leakage lineD.45

Figure 17


14. A hall effect probe measures:a. permeabilityb. conductivityc. tangential field strengthd. flux density perpendicular to the probe surfacee. reluctanceD.50

15. The ratio between the flux density and the magnetic field strength (B/H ratio) is the:a. field strengthb. reluctancec. permittivityd. permeabilitye. relative saturationD.47


16. If the part in Figure 18 has a circular magnetic field, which of thediscontinuities would give the best indication with a rotating flux detectionsystem?a. Ab. Bc. Cd. DA.240


17. If the part in Figure 18 has a longitudinal magnetic field, which of thediscontinuities would give the best indication with a detector coil orientatedacross the part?a. Ab. Bc. Cd. DE.14

18. The best angle for the magnetic field to intersect a discontinuity in a test specimen is:a. 90°b. 60°c. 45°d. 30°A.230/G.289


19. In the flux leakage examination of tubular products using rotating sensorcoils, which of the following discontinuities can be detected?a. longitudinally orientedb. transversely orientedc. sliversd. laminationsG.254

20. In flux leakage testing using search coils, the amplitude of the signalreceived from a discontinuity may be affected by:a. the depth of the discontinuityb. the orientation of the discontinuityc. the distance between the flux leakage sensor and the tubed. all of the abovee. only a and cA.157 /G.323


21. Which of the following describes the type of magnetic field created in apipe by using an encircling magnetizing coil?a. circularb. longitudinalc. vectord. retentive reversalA.231

22. After the pipe leaves an encircling coil, it has which of the following magnetic fields?a. active longitudinalb. Residual longitudinalc. active residuald. transverseA.231


23. The width and amplitude (height) of the signals induced in the searchcoils are affected by which of the following?a. the amount of voltage induced into the test part by the magnetizing coilb. the electrical resistance of the test part materialc. the rate of change in the flux leakage as seen by the detector coild. the amount of current induced into the test part by the magnetizing coilA.388

Comments:Amplitude ∝∆Ф ?


24. Generally, when comparing a detector coil signal from a crack and acorrosion pit, which of the following characteristics would indicate that thesignal is caused by a crack?a. wide base, high amplitudeb. narrow base, low amplitudec. narrow base, high amplituded. wide base, low amplitudeA.388


25. Generally, when comparing a hall effect detector signal from a crack anda corrosion pit of the same depth:a. the crack will produce a higher amplitudeb. the pit will produce a higher amplitudec. they will produce signals of approximately the same amplituded. cracks can not be detected by hall effect detectorsA.154


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 coilD.49

27. Which of the following has the most effect on the amplitude of a rotating detector coil signal?a. drive roller speedb. pipe speedc. rotating head speedd. polarity switch settingA.240


28. In a flux leakage test, assuming that all of the following are in the samerelative position, which would be the hardest to detect?a. a surface crackb. a near-surface crackc. a scratchd. a seamA.388

29. Magnetic flux lines that are parallel to a discontinuity produce:a. strong indicationsb. weak indicationsc. no indicationsd. fuzzy indications8.16


30. Magnetic lines of force:a. travel in straight linesb. are randomly orientedc. form a closed loopd. overlay in highly ferromagnetic materialsB.12

31. A metal that is difficult to magnetize is said to have:a. high permeabilityb. low permeabilityc. high reluctanced. low retentivityB.45


32. The magnetism that remains in a piece of magnetizable material after themagnetizing force has been removed is called the:a. residual magnetismb. tramp magnetismc. damped magnetismd. permanent magnetismB.25

33. Flux leakage inspection is not a reliable method of detecting:a. lapsb. deep internal cavitiesc. cracksd. seams8.233


34. Ferromagnetic material is:a. strongly attracted by a magnet ·b. not highly saturated by magnetic fieldsc. a material with a 0 permeability measurementd. not capable of being magnetizedD.138

35. An electric current through a copper wire:a. creates a magnetic field around the wireb. creates magnetic poles in the wirec. magnetizes the wired. does not create a magnetic field8.18


36. If a current is passed through an electrical conductor, what will surround the conductor?a. an eddy current fieldb. a currentc. a magnetic fieldd. a residual field B.18

37. The strength of the magnetic field induced in a part is often referred to as:a. current densityb. voltagec. flux densityd. retentivityB.15


38. Indications such as those at local vent holes or welds are:a. fake indicationsb. relevant indicationsc. magnetic writing indicationsd. nonrelevant indicationsB.234

39. Which of the following statements is a disadvantage of flux leakage testing?a. it can be used only on ferrous materialsb. it can be applied only to detect surface discontinuitiesc. it can be applied only to detect subsurface discontinuitiesd. it can only detect discontinuities parallel to the magnetic fieldB.2


40. The direction of a magnetic line of force is ____ degrees from the direction of current flow.a. 45b. 90c. 180d. 220B.19

41. Stopping the detector coil directly over a discontinuity will cause the signal to:a. stopb. increasec. go the opposite directiond. stay the sameA.388


42. If a periodic standardization check is unacceptable, what action shouldthe operator take?a. repeat the check without adjustmentb. restandardize and reexamine all pipe run since the last acceptable checkc. restandardize and reexamine all pipe with signals over fifty percent ofreference run since the last acceptable checkd. restandardize and reexamine all pipe run that daye. restandardize and continue the inspection with the next jointF.E-570.5


Recalling the mistakes


Flux Leakage Testing Level II Q&A

TWO


Answers to Flux Leakage Testing Level II


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 wireb. the location of broken wire within the cross sectionc. the gap between the ends of fhe broken wired. all of fhe aboveA.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. parallelb. at an angle of 45"c. perpendiculard. none of the aboveA.153


3. The best discontinuities detection sensitivity is obtained when themagnetizing flux is:a. parallel to the discontinuity's longest dimensionb. perpendicular to the discontinuity's shortest dimension c. perpendicular to the discontinuity's longest dimensiond. none of the aboveA.230/G.289

4. In flux leakage inspection for discontinuities using an active field, the partbeing inspected should be magnetized:a. beyond saturationb. to saturation or near saturationc. well below saturationd. near the point of maximum permeabilityA.49


5. An advantage that flux leakage testing has in comparison with eddy currenttesting is that flux leakage testing is:a. less sensitive to interferences caused by surface roughnessb. useful on products at temperatures above the curie pointc. useful on austenitic steelsd. easier to use on ferromagnetic materialsA.47


6. Using Figure 19, flux leakage strengfh decreases with distance d from thediscontinuity surface and is approximately proportional to:a. db. 1/dc. 1/d2

d. 1/d3

e. 1/d4

H.95


7. Using Figure 20, which notch would produce the highest amplitude signalwhen using a parallel coil or a pair of hall elements connected in opposition?a. Ab. Bc. Cd. DG.327

Amplitude ∝ Depth/Width ?


7. Using Figure FL-6, the relation between the depth (D) of defects and signalamplitude (A) of leakage flux is approximately (K = constant of proportionality):a. A =k 1/Db. A =kDc. A =kD2

d. A =kD3

e. A =kD4

L.54Amplitude ∝ Depth, Amplitude ∝ 1/W, Amplitude = kD/W

Figure FL-6

W


17. The field strength over a crack is directly proportionalto the relative permeability of the steel and the ratio:a. crack depth/crack wtdthb. crack width/crack depthc. crack length/crack depthd. crack length/crack wtdthX.194

B ∝ D/W ?

D

W


8. What particular type of discontinuity would not typically be indicated by fluxleakage techniques?a. lapsb. pitting with crackingc. surface contaminationd. longitudinal seamsA.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 onlyb. the strength of applied current onlyc. the number of turns in the coil and the strength of the applied currentd. the direction of applied current in the coilA.231


10. If the sensor bounces along the surface of above-ground storage tanks, it may:a. make it difficult to estimate fault severityb. generate noise in the signalc. decrease the speed of the inspectiond. distort the magnetizing systemA.388

11. In flux leakage testing, the advautage(s) of electromagnetic magnetizationover permanent magnets is/are:a. Non adjustable magnetic field intensity, lighter, more rugged constructionb. adjustable magnetic field intensity, heavier, more rugged constructionc. adjustable magnetic field intensityd. nonadjustable magnetic field intensity and lighterA.388


12. The current used for magnetization when doing magnetic flux leakageinspection must be a:a. steady non fluctuating current (DC)b. current that reverses direction at a consistent ratec. current that fluctuates on and off at a consistent rated. current that varies based on the thickness of the materialA.387

13. As a general rule, hard (high strength) ferromagnetic materials have:a. high coercive force and are easily demagnetizedb. high coercive force and are not easily demagnetizedc. low coercive force and are easily demagnetizedd. low coercive force and are not easily demagnetizede. none of the abOveE.41


14. The point P shown on the hysteresis loop in Figure 21 is called the:a. coercive forceb. initial permeabilityc. residual field (Remanence)d. leakage fluxe. demagnetization pointE.40


15. The bracketed area shown by R on the hysteresis loop in Figure 21 is called the:a. coercive forceb. initial permeabilityc. residual fieldd. leakage fluxe. demagnetization pointE.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


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


17. The following may be used to detect flux leakage:a. inductive sensor coilsb. magnetic tapec. hall element(s)d. all of the aboveD.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 tubec. passing current through the tubed. all of the abovee. a and b onlyA.230-232


19. In the examination of above-ground storage tanks where the flux sensor ison the top surface:

a. only top surface discontinuities are detectedb. only bottom surface discontinuities are detectedc. both top and bottom surface discontinuities can be detected but generally

cannot be distinguished from each otherd. both top and bottom surface discontinuities can be detected and can

generally be distinguished from each otherA.389


Level II Flux Leakage Testing23. In the examination of tubular products where the flux sensor measuresthe leakage field at the outside surface of the tube:a. OD discontinuities are detectedb. both OD and ID discontinuities may be detectedc. both OD and ID discontinuities can be detected but generally cannot be distinguished from each otherd. both OD and ID discontinuities can be detected and can generally be distinguished from each otherDD.625


20. Reference standards used in the flux leakage examination of tubularproducts should be carefully prepared since the flux leakage signal responsefrom the notch will be affected by:a. notch widthb. notch lengthc. notch depthd. all of the aboveA.277

21. Which of the following is not a discontinuity common to rolled products?a. seamsb. cracksc. cold shutsd. laminationsE.110


22. Forging laps occur in what relation to the axial direction of a part?a. they are always found on the thermal centerlineb. they are found on the surface of a part at a 90° angle to the long axisc. they may occur anywhere in the part and always run in the direction ofworkingd. they may occur anywhere on the surface and may bear no relation tothe axial direction of the partE.115

23. The general term used to refer to a break in the metallic continuity of the part being tested is:a. discontinuityb. crackc. seamd. lapE.109


24. Materials which are weakly repelled magnetically are called:a. diamagneticb. nonmagneticc. paramagneticd. ferromagneticE.6

25. A break in the magnetic uniformity of a part that is called a magneticdiscontinuity is related to a sudden change in:a. resistivityb. inductancec. permeabilityd. capacitanceD.101


26. A hysteresis curve describes the relation between:a. magnetizing force and flux densityb. magnetizing force and applied currentc. strength of magnetism and alignment of domains within materiald. magnetic flux density and the current generatedE.39

27. Inclusions are an example of which kind of discontinuity?a. inherentb. primary processingc. secondary processingd. service8.76


28. Fatigue cracking is an example of which kind of discontinuity?a. inherentb. primary processingc. secondary processingd. serviceB.80

29. Hot tears are associated with:a. castingb. forgingc. weldingd. rolling8.78


30. When inspecting wire rope, a magnetic flux loop is used to monitor:a. broken external wiresb. broken internal wiresc. changes in inspection speedd. reductions in cross-sectional areaB.80

31. The characteristics of the varying magnetic field about an AC energized coil are determined by:a. the number of turns in the coilb. the strength of applied currentc. the size and shape of the solenoidd. all of the aboveC.307


32. Flash line tears are associated with:a. castingb. forgingc. weldingd. rollingB.78


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.)

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 dieswhich 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.

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


Forging of Crank Shaft


Flux Leakage Testing Level III Q&A

Three


1. Which of the following flux sensitive devices is not time dependent?a. long straight wire passing through a magnetic fieldb. search coilc. search coil derivatived. hall elementB.143


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 thanb. the same amplitude asc. a lower amplitude thand. wider thanA.235

Figure 22


4. In Figure FL-10, the flux leakage at slot A will be____ than that at slot B.a. greaterb. Smaller A ∝ D/Wc. broaderd. less readily detectedz.so

FL-10


17. The field strength over a crack is directly proportionalto the relative permeability of the steel and the ratio:a. crack depth/crack wtdthb. crack width/crack depthc. crack length/crack depthd. crack length/crack wtdthX.194

B ∝ D/W ?

D

W


3. Which devices are used to detect flux leakage?a. coils, hall probes and transistorsb. piezoelectric crystals, hall probes and magnetic diodesc. piezoelectric crystals, transistors and magnetic diodesd. coils, hall probes and magnetic diodesG.311


4. In the flux leakage testing of wire rope, a system using an annular coil withintegrator is frequently used (see Figure 23). What is the main reason forusing such a system?a. to compensate for the influence of testing speed variationsb. to find the radial location of wire breaksc. to detect small cracks inside the roped. to detect cross-sectional area changesA.438


5. In a properly operating flux leakage test system, pipe discontinuitiesoccurring at increased depths from the surface will generate signals with:a. increased phase differencesb. higher frequency characteristicsc. lower frequency characteristicsd. increased signal to noise ratiosA.235Udpa, 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).


3.10 EDDY CURRENT TECHNIQUESWhen outside encircling coils are used for testing, the phase of the outersurface discontinuities will lead the phase of identical inner surfacediscontinuities. 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.



6. Lift-off reduces the amplitude of the flux leakage signal. The othersignificant effect it has on the signal is a:a. change in phaseb. change in frequencyc. change in signal to noise ratiod. all of the aboveG.320


3.6 SIGNAL-TO-NOISE RATIOWith flux leakage testing, signal-to-noise ratio is affected by surface noise(the sensor bouncing along the surface) and probe lift-off variations. Lift-offdecreases 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

3.9 COUPLINGAs lift-off or probe clearance increases from the test surface, couplingefficiency and eddy current probe output decreases. Lift-off changes boththe amplitude and phase of the eddy current signal. Impedance changesproduced by small lift-off variations are greatest when the coil is in contactwith the test material. For this reason, spring-loaded probes andselfcomparison coil or differential coil arrangements are frequently used.With eddy current testing, lift-off is a complex variable that can be detectedand compensated for through frequency selection to achieve a desirableoperating point on the complex impedance plane.



7. As shown in Figure 24, a discontinuity having an inclined angle to thesurface has a flux leakage that is:a. lower than a similar normal discontinuityb. equal to a similar normal discontinuityc. higher than a similar normal discontinuityd. all of the aboveB.140


8. Eddy current shielding, the name given to the unidirectional eddy currentflow in products inspected by flux leakage testing, is caused by:a. the interaction between the test magnetic field and a residual field in the productb. fluctuations in the DC magnetizing currentc. rapidly occurring flux changes in the product created by the rotation of the magnetic fieldd. rapidly occurring impedance changes in the pick-up coilsG.280

9. Too high a rotational test speed or too high active pole rotating head speedcan cause the loss of an indication from an ID discontinuity: What can this beattributed to?a. excessive generated surface noiseb. limitations of the flux sensor elementsc. eddy current shieldingd. reverse magnetization effectG.280


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 178mm (7 in.) diameter tube, can have a maximum throughput speed of perminute for 100% inspection coverage.a. 201 rn (660ft)b. 55 m (180ft) 152 x 2 x 180 = 54720mmc. 49 m (162ft)d. 27 m (90ft)I.564,571/J.22A


11. A flux leakage pipe inspection system with two inspection heads, eachhaving 152 mm (6 in.) long inspection areas and rotating at 180 rpm on a 178mm (7 in.) diameter pipe, would require a throughput speed of per minute toprovide 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


12. What has the most influence on the magnetic properties of steel?a. chemistry, microstructure and grain sizeb. cross-sectional area, microstructure and heat treatmentc. cross-sectional area, grain size and chemistryd. heat treatment and lengthB.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.


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 thefollowing materials?a. steelb. copperc. aluminumd. all of the aboveB.127


14. What is the SI unit for magnetic flux density?a. weberb. gaussc. teslad. none of the aboveA.24

15. What is the SI unit for magnetic field strength?a. weber (magnetic flux)b. tesla (magnetic density)c. ampered. ampere per meter (magnetic field intensity)A.24

Charlie C

hong/ Fion Zhang


16. When inspecting wire rope, the annular coil approach measures:a. the magnetic flux in the rope locallyb. the normal component of flux leakagec. the tangential component of flux leakaged. the voltage induced in the rope locallyA.439


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). Thetwo discontinuities have the same dimension and geometry. The signal:a. will be stronger from the outside discontinuityb. will be stronger from the inside discontinuityc. will be the same for both discontinuitiesd. will be stronger from either discontinuity based on the geometry of the discontinuity, wall thickness and permeability of the tubeD.101


18. A ferromagnetic part can be demagnetized by:a. raising its temperature above the curie pointb. withdrawing the part from an AC coilc. alternately reversing and reducing the applied fieldd. all of the aboveE.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 onlyb. signal width onlyc. visual and ultrasonic evaluationd. signal amplitude and widthA.389


20. Permeability of a material can be numerically written as:a. R/Bb. B/Hc. Hc/Hbd. ampere turns/number of turnsD.47

21. Magnetic field intensities for electronic flux leakage testing generally ____ magnetic particle testing.a. are higher than forb. are the same as forc. are lower than ford. have no relationship toB.142


22. Which of the following is not a factor in determining flux leakage?a. discontinuity location with respect to the measurement surfaceb. relative permeability of the materialsc. levels of magnetic field intensityd. density of the materialA.238

23. The sensitivity of a pickup coil is improved by:a. lengthening the coilb. widening the coilc. using a ferrite cored. using a diamagnetic coreA.236


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 45° vector fieldd. the internal field normal to the axis of the coilA.235

25. The reduction in cross-sectional area caused by a discontinuity causes:a. an increase in the internal flux density of the partb. a decrease in the internal flux density of the partc. no change in the internal flux density of the partd. a reversal of direction in the magnetic field at the reduction in cross-sectional areaA.48


26. When using search coils, to reduce or eliminate the signal from a longnonrelevant indication such as the weld trim of electric welded pipe:a. lengthen the coilb. widen the coilc. use a ferrite cored. link two coils wound in opposite directions in seriesG.323


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

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


AbstractMagnetic 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.

■ 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.

■ 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.


Permanent magnet method


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 (out-dated 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.


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


LF sensorsLF 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 sensorLMA 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 cross-sectional 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.


Limitations of magnetic methodThis 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.


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.


EquipmentTwo categories of equipment to test ropes have been supplied: 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


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

FIG 3. MD120 chart recorder


Fig2. GP-series sensing head


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 reputablemanufacturers 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 Polish-made and German heads are equipped with additional channels to estimate the depth inside the rope of a localised loss position.


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 sensortypes 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.


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. MerasterMD120 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.


Meraster MD120 Wire Rope DefectographBased 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).


The Defectograph equipped with a suitable sensing head with a three-channel 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 "localisedlosses" along a rope sector.


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.


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.


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 all-rope 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.


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.


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-push-button.

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.


End of Reading I


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

Designation: E1571-01


1. Scope1.1 This practice covers the application and standardization of instrumentsthat use the electromagnetic, the magnetic flux, and the magnetic fluxleakage examination method to detect flaws and changes in metallic cross-ectional areas in ferromagnetic wire rope products.

1.1.1 This practice includes rope diameters up to 2.5 in. (63.5 mm). Largerdiameters 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, ifany, associated with its use. It is the responsibility of the user of this standardto establish appropriate safety and health practices and determine theapplicability of regulatory limitations prior to use.

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


2. Referenced Documents2.1 ASTM Standards:E 543 Practice for Agencies Performing Nondestructive Testing2E 1316 Terminology for Nondestructive Examinations


3. Terminology3.1 Definitions—See Terminology E 1316 for general terminology applicableto this practice.

3.2 Definitions of Terms Specific to This Standard:3.2.1 dual- Indunction instrument—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)—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.


3.2.3 loss of metallic cross-sectional area (LMA)—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 aninstrument.

3.2.4 single-function instrument—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.


4. Summary of Practice4.1 The principle of operation of a wire rope nondestructive examination instrument is as follows:

4.1.1 AC Electromagnetic Instrument - An electromagnetic wire ropeexamination instrument works on the transformer principle with primary andsecondary coils wound around the rope (Fig. 1). The rope acts as thetransformer core. The primary (exciter) coil is energized with a low frequencyalternating current (ac), typically in the 10 to 30 Hz range. The secondary(search) coil measures the magnetic characteristics of the rope. Anysignificant change in the magnetic characteristics in the core (wire rope) willbe 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 startof an examination. This type of instrument is designed to detect changes inmetallic crosssectional area. (LMA only?)

Keywords:AC Electromagnetic Instrument


FIG. 1 Schematic Representation of an Electromagnetic Instrument Sensor-Head


4.1.2 Direct Current and Permanent Magnet (Magnetic Flux) Instruments—irect current (dc) and permanent magnet instruments (Figs. 2 and 3) supply aconstant flux that magnetizes a length of rope as it passes through the sensorhead (magnetizing circuit). The total axial magnetic flux in the rope can bemeasured either by Hall effect sensors, an encircling (sense) coil, or by anyother appropriate device that can measure absolute magnetic fields orvariations in a steady magnetic field. The signal from the sensors iselectronically processed, and the output voltage is proportional to the volumeof steel or the change in metallic cross-sectional area, within the region ofinfluence of the magnetizing circuit. This type of instrument measureschanges in metallic cross-sectional area. (LMA only as either ∆A or A)


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


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


4.1.3 Magnetic Flux Leakage Instrument—A direct current or permanentmagnet instrument (Fig. 4) is used to supply a constant flux that magnetizes alength of rope as it passes through the sensor head (magnetizing circuit). Themagnetic flux leakage created by a discontinuity in the rope, such as a brokenwire, 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 iselectronically 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.”


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


4.2 The examination is conducted using one or more techniques discussed in4.1. 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.


5. Significance and Use5.1 This practice outlines a procedure to standardize an instrument and touse the instrument to examine ferromagnetic wire rope products in which theelectromagnetic, magnetic flux, magnetic flux leakage, or any combination ofthese methods is used. If properly applied, the electromagnetic and themagnetic flux methods are capable of detecting the presence, location, andmagnitude of metal loss from wear and corrosion, and the magnetic fluxleakage method is capable of detecting the presence and location of flawssuch as broken wires and corrosion pits.

5.2 The instrument’s response to the rope’s fabrication, installation, and in-ervice-induced flaws can be significantly different from the instrument’sresponse 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) realin-service-induced flaws whose characteristics will adversely affect theserviceability of the wire rope.


6. Basis of Application6.1 The following items require agreement by the users of this practice andshould 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.


6.2 Wire Rope Reference Standard (Fig. 5):6.2.1 Type, dimension, location, and number of artificialanomalies to be placed on a wire rope reference standard.6.2.2 Methods of verifying dimensions of artificial anomaliesplaced on a wire rope reference standard and allowabletolerances.6.2.3 Diameter and construction of wire rope(s) used for awire rope reference standard.


FIG. 5 Example of a Wire Rope Reference Standard


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.


FIG. 6 Example of a Rod Reference Standard


7. Limitations7.1 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 ropediameters, the combination (between rope outside diameter and sensor headinside diameter) of which provides an acceptable minimum air gap to assurea reliable examination.


7.2 Limitations Inherent in the Use of Electromagnetic and Magnetic Flux Methods:

7.2.1 Instruments designed to measure changes in metallic cross-sectionalarea are capable of showing changes relative to that point on the rope wherethe 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.


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 withcorrosion 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.


8. Apparatus8.1 The equipment used shall be specifically designed to examineferromagnetic 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 ofmagnetically saturating the range (size and construction) of ropes for which itwas 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.


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 speedoutput indicating the current examination distance traveled and rope speed or,whenever applicable, have a proportional drive chart control thatsynchronizes 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.


9. Examination Procedure9.1 The electronic system shall have a pre-examination standardizationprocedure.

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. Theexamination 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.


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 byinserting 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 arelatively uniform speed. Relevant signal(s) must be recorded on suitablemedia, such as on a strip chart recorder, on a tape recorder, or on computerfile(s), for the purpose of both present and future replay/analysis.


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 whencommencing 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, and9.2.5.13 examination speed.


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 workinglength of the rope, the sensor head should be positioned to maintain thesame magnetic polarity with respect to the rope for all setups. For strip chartalignment purposes, a temporary marker should be placed on the rope at apoint common to the two adjacent runs. (A ferromagnetic marker shows anindication on a recording device.) The same instrument detection signalsshould be achieved for the same standard when future examinations areconducted on the same rope.


9.2.8 When determining percent LMA, it must be understood thatcomparisons are made with respect to a reference point on the roperepresenting maximum metallic crosssectional area. The reference point mayhave deteriorated such that it does not represent the original (new) rope. Thereference point must be inspected visually to evaluate its condition. Whendetermining percent LMA, it must be understood that comparisons are madewith respect to a reference point on the rope that represents the rope’smaximum metallic crosssectional area. The reference point’s condition mayhave deteriorated during the rope’s operational use such that it no longerrepresents the original (new) rope values. The reference point must beexamined visually, and possibly by other means, to evaluate its currentcondition.


9.2.9 If the NDT indicates existence of significant rope deterioration at anyrope location, an additional NDT of this location(s) should be conducted tocheck for indication repeatability. Rope locations at which the NDT indicatessignificant deterioration must be examined visually in addition to the NDT.

9.3 Local flaw baseline data for LF and LMA/LF instruments may beestablished during the initial examination of a (new) rope. Wheneverapplicable, gain settings for future examination of the same rope should beadjusted to produce the same amplitude for a known flaw, such as a rod orwire attached to the rope.


10. Reference Standard10.1 General:10.1.1 The instrument should be standardized with respect to the acceptancecriteria 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 – 10.2 and 10.3 – are useful for laboratory purposes to more fully understand instrument limitations.


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


10.2.2 Artificial flaws placed in the wire rope reference standard shall includegaps 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 aminimum 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 squareand 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.


10.3 Rod Reference Standard:10.3.1 Steel rods are assembled in a manner such that the total cross-ectional area will be equal to the cross-sectional area of the wire rope to beexamined. The rod bundle is to be placed in the sensor head in a mannersimulating the conditions that arise when a rope is placed along the axis ofthe examination head. Individual rods are to be removed to simulate loss ofmetallic area caused by wear, corrosion, or missing wires in a rope. Thisprocedure gives highly accurate control of changes in instrument responseand 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.


10.4 Adjustment and Standardization of Apparatus Sensitivity:10.4.1 The procedure for setting up and checking the sensitivity of theapparatus 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.


10.4.1.5 If standardization is a static procedure, as with an electromagneticinstrument (see 4.1.1), the standard reference rope shall be passed throughthe detector assembly at field examination speed to demonstrate adequatedynamic performance of the examination instrument. The instrument settingsthat provide required standardization shall be recorded.


11. Test Agency Qualification11.1 Nondestructive Testing Agency Qualification—Use of an NDT agency (inaccordance with Practice E 543) to perform the examination may be agreedupon by the using parties. If a systematic assessment of the capability of theagency is specified, a documented procedure such as Practice E 543 shall beused as the basis for the assessment.

12. Keywords12.1 electromagnetic examination; flux leakage; local flaws (LF); Magneticflux; magnetic flux leakage; percent loss of metallic cross-sectional area(LMA); rod reference standards; sensor head; wire rope; wire rope referencestandard


End of Reading II


Remote Field Testing


Remote Field Testing Level I Q&A


1. RFT means:a. Random Field Transitionb. Reluctance Field Testingc. Remote Field Testingd. Remote Fitness TestingB.3.2.5

2. According to ASTM Standard Practice E 2096-00, the definition of remotefield is:a. electromagnetic testing done at remote locationsb. the electromagnetic field which has been transmitted through the testobject and is observable beyond the direct coupling zone of the exciterc. through-transmission eddy currents, detected on the far side of a material or object under test by a remote receiver coild. the opposite of direct fieldB.3.2.4


3. The dominant electromagnetic energy distribution process in RFT is said to be:a. reflected impedanceb. through-transmissionc. piezoelectric energy conversiond. magneto-motive forceD.969,970

4. Eddy currents are induced in any material that is subjected toa. conductive/a constant magnetic fieldb. insulating/a constant electric fieldc. conductive/a time-varying magnetic fieldI.51


5. In a properly designed RFT probe, the detector coil is positioned in the:a. direct field zoneb. transition zonec. remote field zoned. junction between the remote field zone and the transition zoneD.969

6. RFT tube standards:a. must include a permeability variationb. are preferably of the same material, diameter and thickness as the tubes to be examinedc. should have internal and external wall loss reference discontinuitiesd. are always made of SA178 carbon steelB.10.1


7. Frequencies selected for RFT inspections are:a. usually higher than those used in conventional eddy current testsb. usually lower than those used in conventional eddy current testsc. in the same range as those used in conventional eddy current testsd. carefully calculated and must never be changed during an inspectionC.226


8. Compared to a conventional eddy current probe, a typical RFT probe:a. has a larger inter-coil spacingb. requires more protection from vibrationc. generates greater adhesion forces to the tube walld. requires a greater fill factorD.969


9. Reducing the exciter-to-detector coil spacing in an RFT probe will:a. move the detector into the transition zone or direct-coupling zoneb. improve detectability of gradual discontinuitiesc. increase the signal-to-noise ratiod. allow faster tube inspection speedD.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 discontinuitiesb. usually fail to reliably detect external discontinuitiesc. have a very good SIN ratiod. make tube support signals very largeC.227


11. The terminology used to describe the time delay of a received RFT signal with reference to the exciter signal is called:a. magnitudeb. impedancec. phase, phase-shift, phase-lag or phase rotationd. amplitude or log-amplitudeA.80

12. As the field produced by an RFT coil passes through the tube wall, itexperiences:a. amplificationb. attenuationc. flux leakaged. phase increase0.969


13. Eddy current testing is a ____technique while RFT is a ___technique.a. rotation/amplitudeb. reflection/through-transmissionc. reflection/refractiond. pulse-echo/through-transmissionD.969

14. Eddy current testing and RFT are both:a. reflection techniquesb. refraction techniquesc. through-transmission techniquesd. electromagnetic techniquesI.46


15. The term "phase measurement" can mean:a. phase-shiftb. phase anglec. phase-lagd. all of the aboveA.80

16. The skin depth (depth of penetration of the magnetic field into the tubewall where the field has been attenuated to 37% of its initial amplitude) isdependent upon:a. inspection frequency, phase and tube conductivityb. the phase-lag measured at the detector coilc. inspection frequency, tube permeability and tube conductivityd. coefficient of conductivity for the tubeA.80-81


17. Ferromagnetic materials:a. have a relative permeability much less than 1b. include brass, titanium and copperc. are attracted to permanent magnetsd. tend to attenuate a through transmission field less than nonferromagnetic materialsI.481

18. Increasing the RFT operating frequency:a. allows examination of tubing with greater wall thicknessb. always reduces the noise levelc. can give better sensitivity to small discontinuitiesd. increases the thickness of one standard depth of penetration in the materialI.210


19. If an RFT probe is pulled rapidly through a tube:a. the job will get done fasterb. the data will improve due to less noisec. accuracy will increased. small volume discontinuities, like pits, could be missedI.215

20. What is the effect of lowering the frequency of an RFT system?a. the detector signal will get smallerb. the probe can be pulled fasterc. the probe can be used to inspect thicker materialsd. signals from tube support plates will get smaller1.214


Remote Field Testing Level II Q&A

TWO


1. One method that may help improve signal-to-noise ratio is to:a. increase the drive voltage to the exciterb. adjust the strip chart display settingsc. pull the probe through the tubes fasterd. select a probe with a fill-factor less than 0.5C.225

2. A simple RFT probe has one exciter and one detector coil. A longcircumferential 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 thediscontinuity. The phase shift will now be:a. 25°b. 50°c. 100°d. 200°C.226


3. The two signal components that are indicators of overall wall thickness lossare:a. sample rate and signal amplitudeb. phase and amplitudec. signal strength and coil impedanced. the frequency and noise level of the signalB.9.4.2

4. With basic exciter-detector RFT probes, short volumetric discontinuities usually create:a. a near-zero signalb. a double peak in strip chart datac. a decrease in conductivityd. an indication that is seen by the exciter and the detector simultaneously1.221


5. An effective approach to characterize discontinuities is to:a. compare both phase and amplitude informationb. note amplitude deflections alone (because phase is less reliable)c. identify regions where the signal-to-noise level is lowd. use all X-Y deflections larger than 1.0 V that are between 0° and 40°I.220

6. One-sided metal loss:a. creates indications that extend towards the zero-signal pointb. creates indications similar to wall thickeningc. is created by instrument noised. creates a phase deflection greater than a log-amplitude deflectionI.221


7. Baffle plates or support plates:a. are usually nonconducting and nonferromagnetic and do not affect the RFT signalb. have an indication very similar to metal lossc. cause a deflection in the amplitude trace in the metal loss directiond. reduce the through-transmission process dramatically1.222


8. A discontinuity indication that lies along the reference spiral on the voltage plane is usually:a. one sidedb. pittingc. permeability variationd. uniform wall lossI.221-222

9. When performing an RFT exam using a RFT voltage plane display, thenominal point is positioned at X-Y coordinates:a. (1,0)b. (0, 1)c. the air point, rotated to lie on the negative Y axisd. where the reference curve meets 0,0G.4/1.217-218(Fig. 19),220


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 coordinatesb. the frequency and drive voltage along the x and y axes, respectivelyc. the probe air-signal placed at the origind. probe lift-off noise along the X axisG.4


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 closelyc. do not change in the presence of metal lossd. are rotated by accumulations of nonmagnetic, nonconducting debris1.219


13. The differential channel signal is best for:a. small-volume discontinuity detection like pits and cracksb. long, gradual wall loss, such as steam erosionc. one-sided wall loss like mid-span erosiond. under-TSP discontinuity detectionI.219

14. An X-Y output display:a. shows signals that are linearly proportional to wall lossb. can indicate the circumferential extent of discontinuitiesc. shows the relationship between discontinuity area and depth clearlyd. none of the aboveB.9.4.2


15. The length (or height) of the signal on the voltage plane polar plot may be related to:a. the circumferential extent of the discontinuityb. the depth of the discontinuityc. the temperature of the tube materiald. either a or bI.220

16. The following discontinuities are likely not detectable with RFT:a. mid-span erosionb. steam impingement erosionc. tubesheet wormholingd. general corrosionI.222


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


18. The circumferential extent can only be displayed accurately with:a. differential signals on an X-Y displayb. absolute signals on an X-Y displayc. absolute signals on a voltage plane with a ref curved. MIX signals on an X-Y displayI.219-220

19. Eddy current systems can be used effectively to inspect high permeabilitytubes without magnetic saturation:a. trueb. falsec. only true if slow pull speeds are usedI.215(Table 1)


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, lowconductivity tubesb. false: a higher frequency technique such as eddy current would give better phase separationc. only true if magnetic saturation probes are usedI.481

21. When using RFT to inspect boiler tubes:a. the bend areas cannot be inspectedb. the bend areas can be inspected if a comparison technique is used to other tubes with similar bendsc. the probe must contain magnets to reduce the permeability valueF(Fig. 2)


22. At a probe pull speed of 20 cm (7.9 in.) per second with the instrumentsample rate set to 40 samples per second, the distance between datasampling 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


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

Designation: E 2096-05


1. Scope1.1 This practice describes procedures to be followed during remote fieldexamination of installed ferromagnetic heatexchanger tubing for baseline andservice-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 regardedseparately as standard. The values stated in each system may not be exactequivalents; therefore, each system shall be used independently of the other.Combining values from the two systems may result in nonconformance withthe standard.


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

2. Referenced Documents2.1 ASTM Standards: 2E 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 TestingPersonnel Qualification and Certification

Can CGSB-48.9712-95 Qualification of Nondestructive Testing Personnel, Natural Resources Canada4


3. Terminology3.1 General—Definitions of terms used in this practice can be found inTerminology 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.


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

3.2.5 remote field testing, n—a nondestructive test method that measureschanges 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 asthe “operator” and “customer,” respectively.


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


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



A



B


3.3.4 RFT system, n—the electronic instrumentation, probes, and all associated components and cables required for performing RFT.

3.3.5 RFT system reference standard, n—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, n—a standard used in addition to theRFT system reference standard, with artificial or service-induced flaws, usedfor flaw characterization.


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


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.

Keywords:Zero PointNominal point


4. Summary of Practice4.1 The RFT data is collected by passing a probe through each tube. Theelectromagnetic field transmitted from the exciter to the detector is affected bydiscontinuities; 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 atregular intervals during the examination. Data and system settings arerecorded in a manner that allows archiving and later recall of all data andsystem settings for each tube. Interpretation and evaluation are carried outusing one or more flaw characterization standards. The supplier generates afinal report detailing the results of the examination.

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

characterization standards.


5. Significance and Use5.1 The purpose of RFT is to evaluate the condition of the tubing. Theevaluation results may be used to assess the likelihood of tube failure duringservice, a task which is not covered by this practice.

5.2 Principle of Probe Operation—In a basic RFT probe, the electromagneticfield emitted by an exciter travels outwards through the tube wall, axiallyalong the outside of tube, and back through the tube wall to a detector(Fig. 2a).


RFT

Operation—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

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


FIG. 2 RFT Probes

NOTE 1—Arrows indicate flow of electromagnetic energy from exciter to detector. Energy flow is perpendicular to lines of magnetic flux.


FIG. 2 RFT Probes


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 mainlyaxially, or

(3)discontinuities interrupt the eddy currents, which flow mainlycircumferentially.

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.


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 “nominal tube” 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.


5.4 Probe Configuration—The detector is typically placed two to three tubediameters from the exciter, in a location where the remote field dominates thedirect-coupling field. Other probe configurations or designs may be used tooptimize flaw detection, as described in 9.3.

5.5 Comparison with Conventional Eddy-Current Testing— 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.


6. Basis of Application6.1 Personnel Qualification:6.1.1 Personnel performing examinations to this practice shall be qualified asspecified 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.


6.1.3 Recommendations for qualification as an RFT dataanalyst (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 byASNT 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.


NOTE 1—At the time of approval of this practice, no nationally orinternationally recognized guideline for personnel qualification in RFT wasavailable.

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 thecontractual agreement, NDT agencies shall be qualified and evaluated asdescribed in Practice E 543, with reference to sections on electromagnetictesting. The applicable edition of Practice E 543 shall be specified in thecontractual agreement.


7. Job Scope and Requirements7.1 The following items may require agreement between the using partiesand 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 beexamined.

7.1.4 A tube numbering or identification system.


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 referencestandards 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 theresponsibility of the purchaser; Common sources of noise that may interferewith the examination.

NOTE 3—Nearby welding activities may be a major source of interference.


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.


8. Interferences8.1 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 aotential 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 theelectromagnetic response measured during RFT. The conductivity andpermeability of tubes with the same grade of material are often measurablydifferent. It is common to find that some of the tubes to be examined arenewer tubes with different material properties.


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


8.2.4 RFT is affected by residual magnetism in the tubing, including residualmagnetism created during a previous examination using another magneticmethod. Tubes with significant residual magnetism should be demagnetizedprior 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 themechanical 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 atube.

NOTE 4—Interference from ferromagnetic or conductive objects can beof practical use when RFT is used to confirm the position of an objectinstalled on a tube or to detect where objects have become detached andhave fallen against a tube.


8.3.2 Neighboring Tubes:8.3.2.1 In areas where there is non-constant tube spacing (bowing) or wheretubes cross close to each other, there are indications which may be mistakenfor 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 falseindications or obscure flaw indications should be removed.


8.4 Tube Geometry Effects:8.4.1 Due to geometrical effects (as well as to the effects of permeabilityvariations described in 8.2.2), localized changes in tube diameter such asdents, bulges, expansions, and bends create indications which may obscureor 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 Effect—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.


8.5 Instrumentation:8.5.1 The operator should be aware of indicators of noise, saturation, orsignal distortion particular to the instrument being used. Special considerationshould 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 Offset—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 arecompared.


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.


9. RFT System9.1 Instrumentation—The electronic instrumentation shall be capable ofcreating exciter signals of one or more frequencies appropriate to the tubematerial. The apparatus shall be capable of phase and amplitude analysis ofdetector outputs at each frequency, independent of other frequencies in usesimultaneously. The instrument shall display data in real time. The instrumentshall be capable of recording data and system settings in a manner thatallows archiving and later recall of all data and system settings for each tube.

9.2 Driving Mechanism—A mechanical means (manual allows?) of traversingthe probe through the tube at approximately constant speed may be used.


9.3 Probes—The probes should be of the largest diameter practical for thetubes being examined, leaving clearance for debris, dents, changes in tubediameter, and other obstructions. The probes should be of an appropriateconfiguration and size for the tube being examined and for the flaw type ortypes to be detected. Probe centering is recommended.

9.3.1 Absolute Detectors—Absolute detectors (Fig. 2c) are commonly used tocharacterize and locate large-volume and gradual metal loss.

9.3.2 Differential Detectors—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.


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.


9.3.4 Exciter and Detector Configurations—Probes may have multipleexciters and detectors in a variety of configurations (see, for example, Fig. 2b).These configurations may reduce interference from support plates and otherconductive objects.


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

9.4.2 Strip Charts—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 1b


10. RFT Tube Standards10.1 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 atube standard identical to the tubes to be examined is not available, ademonstration of examination equivalency is recommended. Subsection11.6.2 specifies how to determine if a reference tube of different properties isappropriate 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 Holes—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).


FIG. 3 Typical Artificial Discontinuities Used for Flaw Characterization Reference Standards NOTE 1—Not to scale.


10.3.2 Circumferential Grooves—A circumferential groove is an area of metalloss whose depth at any axial location is uniform around the tubecircumference. Short grooves, with a maximum axial length of less than onehalf a tube diameter, may be used to simulate small-volume metal loss.Grooves with an axial length of several tube diameters may be used tosimulate uniform wall loss (Fig. 3b).

10.3.3 One-Sided Flaws—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).


10.4 RFT System Reference Standards—Flaw depths are specified by givingthe deepest point of the flaw as a percentage of the measured average wallthickness. 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:


10.5.1.1 Through-Hole—A through-hole (Fig. 4, Flaw A) whose diameter isequal to the tube wall thickness multiplied by a specified factor. For tubes ofoutside diameter less than 1.000 in. [25.40 mm], the factor is 1. For tubes ofoutside diameter greater than or equal to 1.000 in., the factor is 1.5.

10.5.1.2 Flat-Milled Flaw—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.


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]. Edgesshall 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°.


10.5.1.6 Long Circumferential Groove—A long circumferential groove (Fig. 4,Flaw F) of a depth of 20 % and recommended axial length of two tubediameters. Length is optional in accordance with application. Edges shall beangled 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 Plates—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 plateshould 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.


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.


11. Procedure11.1 If necessary, clean the inside of the tubes to remove obstructions andheavy ferromagnetic or conductive debris.

11.2 Instrument Settings: 11.2.1 Operating Frequency—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).


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 (aspermitted 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 ofmetal 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 minimumrequired 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.


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 theambient noise by a factor of at least 3, unless otherwise specified by thepurchaser. An exception may be made when the purchaser requires only alarge-volume metal loss examination, in which case, sensitivity should bedemonstrated for specified large-volume flaws on the RFT system referencestandard.

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 producerepeatable indications.


11.5.1 Record data and system settings in a manner that allows archiving andlater recall of all data and system settings for each tube. Throughout theexamination, data shall be permanently recorded, unless otherwise specifiedby 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 nominalexamined tube:


11.6.1.1 The amplitude and angular position of a support plate indication onthe 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—For an alternate method of compensating for differences indimensional 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.


11.7 Compensation for Ferromagnetic or Conductive Objects:11.7.1 Techniques that may improve RFT results near interferingferromagnetic 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).


11.8 System Check—At regular intervals, carry out a system check using theRFT system reference standard to demonstrate system sensitivity andoperating parameters to the satisfaction of the purchaser. Carry out a systemcheck prior to starting the examination, after any field compensationadjustments in accordance with 11.6, at the beginning and end of each workshift, when equipment function is in doubt, after a change of personnel, after achange of any essential system components, and overall at a minimum ofevery four hours. If the flaw responses from the RFT system referencestandard have changed substantially, the tubes examined since the lastsystem check shall be reexamined.


11.9 Interpret the data (identify indications).

11.10 Note areas of limited sensitivity, using indications from the RFT systemreference 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 appropriatecomplementary method or technique to obtain more information, adjusting results where appropriate.

11.13 Compile and present a report to the purchaser.


12. Report12.1 The following items may be included in the examination report. All thefollowing information should be archived, whether or not it is required in thereport.

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.


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 bereferenced 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.


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 offlaws as specified in the purchasing agreement. 12.1.14 Complementaryexamination results that influenced interpretation and evaluation.

13. Keywords13.1 eddy current; electromagnetic testing; Ferromagnetic tube; remote field testing; RFT; tube; tubular products


End of Reading III


Three

Remote Field Testing Level III Q&A


1. The symbol δ stands for:a. relative magnetic permeabilityb. conductivityc. resistivityd. standard depth of penetrationA.78

2. If δ increases, it likely means that:a. frequency has increasedb. permeability has decreasedc. conductivity has decreasedd. either b or cA .80


3. The symbol used for relative permeability IS:a. δb. μc. σd. ρA.78

The symbol used for resistivity is:a. δb. μc. σd. ρA.78


5. Local permeability changes caused by stress in the tube will probably:a. change the operating frequencyb. produce a signal to the right of the voltage plane reference curvec. rotate the signals CCWd. have no effect because they are minor in comparison to wall loss signalsB.2(Fig. 1A)

6. Narrow grooves next to a TSP (tube support plate) are often called:a. baffle wearb. crevice corrosionc. condensate groovingd. midspan erosionI.221


7. RFT gives approximately equal signals (phase and amplitude) for internaland external discontinuities of the same depth and area:

a. trueb. falseD.969


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 thephase-amplitude diagram, set the frequency to obtain a difference of 50 to120° between the angles of indication for the reference through-hole (FlawA 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).


Designation: E 2096 – 05


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 surfaceb. 37% of the signal strength at the surfacec. 19% of the signal strength at the surfaced. it does not affect the amplitude; it just delays the phase of the signalA.80


10. Phase lag can be described as:a. the speeding up of the eddy current signal is dense solidsb. the speed of rotation of the probec. the time delay of the electromagnetic energy as it moves deeper in a conductive materiald. the interaction between signal angle and magnitudeI.214

11. How many degrees of phase shift have occurred at the 3δ point?a. 171.9b. 100.3c. 57.3d. 37.4A.81


12. The probe drive current is measured in:a. voltsb. ohmsc. ampsd. gigahertzI.22(Table 6),209

13. A "standard depth of penetration" is sometimes referred to as:a. phase lag at 57%b. 6"c. skin depthd. skin deepA.80


14. The terminology that most accurately defines the coupling of the coil'selectromagnetic energy into the test material is:a. reflection methodb. inductionc. standard depthd. reductionC.226

15. Magnetic liues of flux are often measured in units of:a. gaussb. siemensc. resistivityd. conductanceI.22,24


16. Place the following materials in orderbased on their conductivity (from highestto lowest):a. steel, aluminum, titanium, copperb. aluminum, copper, titanium, steelc. copper, aluminum, steel, titaniumd. titanium, steel, copper, aluminumA.90-94

17. The operating or "nominal reference“ point of the X-Y display of an absolute detector is referenced as:a. the lower left-hand quadrantb. 0,0c. 1,0d. 10,01.218


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

19. Detector coils placed in the"transition zone" will:a. produce larger, more reliable differential signals than a coil in the remote zoneb. produce unpredictable signalsc. produce a saturated signal for alldiscontinuities due to its proximity tothe exciterd. not produce any signalI.213


20. Detailed maps of the magnetic flux distribution within the tube wall can beproduced with:a. Gauss metersb. RFT detector coilsc. FEA (Finite Element Analysis) routinesd. magnetographsD.974


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 tubec. the through-transmission field moving from the OD to the ID surface of thetubed. residual magnetic eventsI.211-214


22. The term "phase;' as defined by ASTM E 1316, Section C, is:a. the vector position on an impedance planeb. a time delay expressed in terms of a 360º AC cyclec. the X-Y coordinates of a signal on a voltage plane displayd. the vector value from 0,0 on an X-Y impedance plane displayA.80


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. trueb. falsec. only true if a magnetic saturation eddy current test was usedd. only true if the saturation coil was DC (rather than an AC coil)B.8.2.4


24. Phase-amplitude diagram can also mean:a. impedance plane displayb. voltage plane polar plotc. X-Y displayd. any or all of the aboveB.3.3.3

25. In RFT testing, the sample rate signifies:a. the probe pull speedb. the rate at which data is digitized for display and recordingc. the cost of taking a sample of datad. the number of tubes that can be inspected on a shiftB.3.3.6


26. "Zero point" means:a. the crossing of the X and Y axes on an impedance plane displayb. the point on the phase-amplitude diagram representing no signal changec. the position of the probe in the tube where there is zero output voltaged. any or all of the aboveB.3.3.8

27. The following factors may affect the response of an RFT probe:a. temperature history of the tube being testedb. conductivity variations in the material under testc. permeability changes caused by cold workingd. all of the aboveB.8.2.1-2


28. The "nominal point" on the phase amplitude diagram, or voltage plane, is:a. the same as the "null" or "balance“ pointb. the point that represents normal wall thickness of a tubec. any point that nominally represents a reference positiond. any measurement with respect to the 0,0 positionB.3.3.2


29. The proximity of other tubes in a heat exchanger is known as the:a. bundle effectb. proximity effectc. shielding effectd. offset effectB.8.3.2.2

30. RFT end effect is:a. the signal obtained from the last tube to be testedb. a large signal, similar to a TSP signalc. the signal from the end of a tube when there is no tube-sheet to shield thesignald. the signal from a wear scar under a TSP8.8.4.3


31. Instrument-induced phase offset is defined as:a. the overall signal phase, as modified by the circuits in the instrumentb. the frequency dependent time delay (which appears as a constant phase offset) due to the amplification and filtering processes in the RFTinstrumentc. the signal angle, rotated by the operator, using the phase rotator control of the instrumentd. the signal seen due to the interference of one channel with anotherB.8.5.2

32. A simple absolute probe:a. contains two coils wound in oppositionb. contains only one detector coilc. can detect small volume discontinuities better than differential probesd. uses an array of self-referencing, pancake detector coilsB.9.3.1


33. Array probes:a. are used for tubes under 0.375 in. (9.525 mm) diameterb. contain multiple coils that interrogate a small section of the tube wallc. are used in explosive atmospheres where they need to be intrinsically safed. measure the radial field onlyB.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 minimumrequirement (as per ASTM E 2096-00):a. a through-wall hole, 0.375 in. (9.525 mm) diameterb. a narrow 20% deep, circumferential groovec. a milled-flat of 50% depth, with an axial length of one half the tube ODd. both b and cB.10.5


35. Reference standards should be:a. stored and shipped carefully to prevent mechanical damageb. machined carefully to avoid localized over-heating and cold workingc. serialized with a unique number as well as the tube OD, metal type andwall thicknessd. all of the aboveB.10.7

36. An X-Y voltage plane display is being used to perform an RFT exam. Ifphase is a parameter that is being measured, a good choice of frequencywould be one that sets the signal from the 20% short circumferential groove inthe reference standard to:a. 90"b. 40°c. between 18° and 22°d. aligned with the X axisB.11.2.1.2


37. You are operating an RFT system and notice that discontinuity signals areunpredictable. You suspect that the detector is operating in the transitionzone. What can you do to get the detectors operating in the remote field zone?a. increase the frequencyb. increase drive voltage to the exciterc. decrease detector gaind. decrease the frequencyD.976

38. External and internal fluids, gas, oil or salt water will severely degrade the RFT signal:a. trueb. falseC.225-230


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. trueb. falseC.225-230

40. Local discontinuities such as pits will produce signals from an absolute probe:a. of high amplitude with open loopsb. of high amplitude with closed loopsc. of low amplitude, to the left of the reference curved. of low amplitude, following the reference curveH.656(Fig. 5)


41. RFT may be used on ferrous and nonferrous tubes with approximatelyequal sensitivity to internal and external discontinuities:a. trueb. falsec. only true if the impedance technique is usedD.976

42. Optimum RFT inspection frequencies will produce:a. ten times the skin depth for one transit of the tube wall thicknessb. approximately one skin depth for one transit of the tube wall thicknessc. approximately 1/4 the skin depth for one transit of the tube wall thicknessd. approximately 1/2 the skin depth for one transit of the tube wall thicknessE.80


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 measuredb. will substantially affect the amplitude of the signal as fill factor gets smallerc. affects both phase and amplitude equallyd. both a and b are trueE.85

44. When using the RFT reference curve and an absolute probe, general, tapered wall loss will:a. lie inside the curveb. lie outside the curvec. closely follow the curved. probably follow the curve for much of the signalH.656(Fig. 5)


45. When using the RFT reference curve and an absolute probe, permeability variations will:a. usually fall outside the curve, to the rightb. produce equal phase and logamplitude signalsc. comprise signals that are inside the curve, approaching the 0,0 pointd. comprise multiple signals responding in random directionsH.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 curveb. the indication may be reduced in amplitude to the point where it is undetectablec. the depth prediction may be nonlineard. this is a fallacy, since the phase angle will still represent true remaining wallH.655


making


Good Luck

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