Electromagnetic testing q&a 004

Charlie Chong/ Fion Zhang

Electromagnetic TestingQuestions & Answers -004 Part 1ACFM,EC & FL,RF Testing-Book(E) 2009My ASNT Level III Pre-Exam Preparatory My Self Study Notes 5th August 2015


Petrochemical Applications



http://www.nbcnews.com/storyline/ukraine-crisis/chemical-plant-near-donetsk-eastern-ukraine-hit-explosion-n302821

Greek Alphabet


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

Fion Zhang at Shanghai5th August 2015

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



IVONA TTS Capable.

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


My Mangoes


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


ACFM-Alternating CurrentMeasurement Testing


ACFM Level I Q&A


Answers to ACFM Level I1.d 2.a 3.d 4c 5.b 6.c 7.a 8.d 9.c10.d 11.b 12.a 13.c 14.d 15.a 16.b 17.c 18.c19.b 20.c 21.d 22.a 23.b 24.d 25.a 26.a 27.b28.b 29.d 30.b 31.c 32.a 33.b 34.b 35.a36.c 37.d 38.d 39.a 40.c 41.b 42.a 43.b 44.d 45.d46.b 47.a 48.c 49.d 50.c


1. Which of the following frequencies has the least depth of penetration?a. 5 kHzb. 50 kHzc. 5 Hzd. 5 MHzB.2.23/D.318

2. Which of the following wires will have the greatest resistance?a. 0.158 cm (0.062 in.) diameterb. 0.318 cm (0.125 in.) diameterc. 0.635 cm (0.250 in.) diameterd. 1.27 cm (0.500 in.) diameterE.15


3. Wbich of the following cable lengths will have the greatest resistance?a. 15.2 cm (6 in.)b. 45.7 cm (18 in.)c. 61.0 cm (24 in.)d. 142.2 cm (56 in.)E.15

4. Wbich of the following materials has the greatest depth of penetrationa. aluminumb. copperc. stainless steeld. steelB.2.24/D.318


5. When the permeability (μ) of a material is increased, the depth of penetration does which of the following?a. increasesb. decreases δ=1/ √(πfμσ)c. remains constantd. increases the conductivityD.319

6. What is required in one circuit to change the current in an adjacent circuit?a. a continuous current must flowb. the resistance in both circuits must increasec. there must be a change in the current in the original circuitd. the magnetic field remains constantB.2.4/D.315


7. What is the effect of increasing the number of turns of wire in a coil?a. the magnetic field produced will increaseb. the magnetic field produced will decreasec. the magnetic field will remain constant Ф=N∙I/S, S= reluctanced. there will be a change in the electric currentE.14/H.331·332

8. What is the symbol for conductivity?a. Vb. Ωc. μd. σE.57


Reluctance.Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits. It is analogous to resistance in an electrical circuit, but rather than dissipating electric energy it stores magnetic energy. In likeness to the way an electric field causes an electric current to follow the path of least resistance, a magnetic field causes magnetic flux to follow the path of least magnetic reluctance. It is a scalar, extensive quantity, akin to electrical resistance. The unit for magnetic reluctance is inverse henry, H-1.

In a DC field, the reluctance is the ratio of the "magnetomotive force” (MMF) in a magnetic circuit to the magnetic flux in this circuit. In a pulsating DC or AC field, the reluctance is the ratio of the amplitude of the "magnetomotive force” (MMF) in a magnetic circuit to the amplitude of the magnetic flux in this circuit. (see phasors)

S = N∙I/Ф, Ф = N∙I/S, F =N∙I

whereS is the reluctance in ampere-turns per weber (a unit that is equivalent to turns per henry). F is the magnetomotive force (MMF) in ampere-turnsФ is the magnetic flux in webers.

"Turns" refers to the winding number of an electrical conductor comprising an inductor

1/Henry = ampere/ weber, Henry= Weber/ampere?

http://en.wikipedia.org/wiki/Magnetic_reluctance


9. Wbat is the symbol for permeability?a. Hb. Bc. μd. IE.47


10. Which of the materials having the following relative permeability (μr) values will be the most easily magnetized?a. 60b. 240c. 800d. 1000E.47,62

11. When an electric current flows through a conductor, in which direction is the magnetic field set up?a. parallel to the conductorb. at 90 degrees to the current flowc. in the opposite direction to the current flowd. in the same direction as the current flowE.43


12. If the current passing through a fixed number of turns is increased, whatwill be the effect on the magnetic field?a. the magnetic field will increase Ф = NI/Sb. the magnetic field will decreasec. the magnetic field will remain constantd. the magnetic field will change directionD.315

13. Which of the following has no effect on the inductance of a coil?a. increasing the number of turnsb. increasing the coil diameter L = μN2A/l https://en.wikipedia.org/wiki/Inductance

c. increasing the currentd. decreasing the number of turnsE.13


14. The depth of penetration in a material will be reduced by:a. increasing the permeabilityb. increasing the conductivityc. increasing the frequency of the testd. all of the aboveB.2.22-23/E.84

15. When a primary coil is brought close to a conductive material, what is the effect on the secondary magnetic field?a. it will be opposite to the primary magnetic fieldb. it will be opposite to the primary electric fieldc. it will be smaller but in the same directiond. it will be larger but in the same direction8.2.2/0.319


16. What is the coupling medium between an alternating current field measurement probe and a metal surface when operating in air?a. an electric currentb. magnetic fieldc. noned. airA.250(Fig. 1)

17. "What generates a magnetic field in the Bz direction?a. uniform surface currentsb. increasing surface currentsc. curvature in the X and Y surface currentsd. decreasing surface currentsF.1


18. What is the predominant electromagnetic property of a ferromagnetic material?a. resistanceb. conductancec. high permeabilityd. a high frequency constantE.44


19. If a current is flowing in a surface, then the magnetic flux density in the X direction is proportional to:a. the current in the X directionb. the current in the Y directionc. the curvature of the current in the X-Y planed. the magnetic flux direction in the Z directionA.251

20. In what way does the magnetic field used for magnetic particle inspection differ from the one produced during alternating current field measurement inspection?a. it is equal and oppositeb. it is in the same directionc. it is at 90 degrees to the alternating current field measurement magneticfieldd. it is at 90 degrees to the surface of the materialA.230,251


20. In what way does the magnetic field used for magnetic particle inspection differ from the one produced during alternating current field measurement inspection?a. it is equal and oppositeb. it is in the same directionc. it is at 90 degrees to the alternating current field measurement magneticfieldd. it is at 90 degrees to the surface of the materialA.230,251

The induced magnetic field run parallel to defect inducing Bzsignals at crack tips – indicating crack length, Bx indicating depth.


The perturbated uniform electric field and the induced magnetic fields Bx, Bz

Bz

Bz


Experiences in the use of ACFM for Offshore Platform Inspection in Brazil

http://www.ndt.net/article/wcndt00/papers/idn233/idn233.htm


Simple Semi Elliptical Model

http://www.shipstructure.org/pdf/91symp22.pdf

Bmax = a ?


The Bx & Bz Display


21. What is the symbol for resistance?a. Hb. Vc. Id. RE.15

22. Which of the following materials has the smallest depth of penetration for an applied AC magnetic field?a. mild steelb. stainless steelc. aluminumd. copper8.2.22-24/0.318


23. Which of the following best describes stainless steel?a. high permeability- low conductivityb. low conductivity- low permeabilityc. high conductivity - low permeabilityd. high permeability- high conductivityB.2.19,24

24. Which of the following statements is correct?a. the conductivity of a metal is proportional to the applied magnetic fieldb. the resistance in a circuit does not affect the current through the circuitc. a varying electric current cannot produce a current in an adjacent circuitd. the magnetic field produced by a current is proportional to themagnitude of the current Ф= NI/SE.13


25. If it is required to generate a uniform electric field parallel to the weld, what direction will the magnetic field have to be to generate this electric field?a. at 90 degrees to the weld and parallel to the surfaceb. parallel to the surface and parallel to the weldc. a circular coil above the surface parallel to the weldd. a circular coil above the surface perpendicular to the weldA.251

26. If a current is flowing in a surface and the magnetic flux density is in the Y direction, what change would produce an effect?a. a change in the current in the X directionb. a change in the magnetic flux density in the X directionc. a nonmetallic coatingd. a change in the current in the Z directionA.251


27. Which of the following NDT methods or techniques can be used to estimate crack depth?a. MPIb. AC field measurementc. dye penetrant inspectiond. ultrasonic creep wave inspectionA.253


28. During an alternating current field measurement weld inspection, themeasurement of crack depth requires the following information:a. the frequency of the inspectionb. the length of the crackc. the depth of penetration of the AC fieldd. all of the aboveF.8

Note: frequency f is not important!


29. What is the indication produced in the magnetic field component representing crack depth that shows that a crack is present?a. the magnetic field is uniformb. the magnetic field is zeroc. the magnetic field value is greater than the background field valued. the magnetic field value is lower than the background valueF.6


30. For accurate depth sizing when using electrical or electromagnetic inspection methods, what must the relationship between the crack length and depth be?a. they must be equalb. the length must be equal to or greater than twice the depth of the crackc. the crack depth must be more than 1.3 cm (0.5 in.)d. the crack length must be less than 5.1 cm (2.0 in.)A.258


31. When a crack is detected in a ferrornagnetic material in an applieduniform magnetic field parallel to the weld and the crack is inclined to the toe of the weld, a magnetic field perpendicular to the surface (Bz) is produced at the crack ends. What form does the field take?a. a -ve peak at both endsb. a +ve peak at both endsc. a large +ve peak at one end and a small -ve peak (trough) at the other endd. large +ve peaks at each end and a –ve peak in the centerF.3

magnetic field parallel to the weld weld

clock-wise current rotation gives peak (+ve) – at weaker magnitude

Current flow


8.9 Crack Geometry Effects:8.9.1 A discontinuity at an angle to the scan—a discontinuity at an angle tothe scan will reduce either the peak or the trough of the Bz as the sensorprobe only passes through the edge of one end of the discontinuity. Thisproduces an asymmetric X-Y plot. Additional scans may be made along theweld or parent plate to determine the position of the other end of thediscontinuity.



Current flow


The Bx & Bz Display

magnetic field

current flow


32. For accurate depth sizing, why must the length of a crack always be greater than twice the depth during alternating current field measurement inspection?a. to give sufficient current flow under the crack centerb. the depth of the crack depends on the lengthc. no current will flow if the crack is too shortd. to give sufficient current flow around the crack endsA.258

33. What effect would you expect if the coils in an AC field measurement probe were smaller and closer together?a. no effectb. improved detection of smaller discontinuitiesc. improved sizing on larger discontinuitiesd. smaller Bx signalsA.255


34. When using the alternating current field measurement inspection technique, what is the most important value that is measured?a. phase angleb. amplitude of the Bx magnetic fieldc. amplitude of the Bz magnetic fieldd. depth of the crackA.251

the most important value that is measured ?

BxD

L


35. If a hysteresis loop were produced for a conductive material and the loop was wide, it could be said that the material has:a. low permeability and would be difficult to magnetizeb. high permeability and would be easy to magnetizec. high permeability and would be difficult to magnetized. none of the aboveE.47

Charlie Chong/ Fion Zhang http://www.ndt.net/article/v08n09/wong/wong.htm


36. The AC field measurement technique differs from other crack detectiontechnologies in that it measures:a. the through thickness dimensionb. the length only of a crackc. the length of the crack beneath the surfaced. detection onlyA.253

37. Electromagnetic test methods can be used for which of the following applications?a. cracks in nonmagnetic materialsb. cracks in magnetic materialsc. cracks in coated materialsd. all of the aboveA.13,424/D.314

?


37. Electromagnetic test methods can be used for which of the following applications?a. cracks in nonmagnetic materialsb. cracks in magnetic materialsc. cracks in coated materialsd. all of the aboveA.13,424/D.314


38. In which of the following environments can AC field measurement inspections be performed?a. waterb. airc. elevated temperaturesd. all of the aboveA.248,385/G.214

39. If a transverse discontinuity is detected in a longitudinal weld, the Bx indication:a. produces an increase in the magnetic fieldb. produces a reduction in the magnetic fieldc. has no effect on the magnetic fieldd. reduces the magnetic field to zeroF.3


40. When an electric current flows down a wire, what is associated with it?a. an electric current flowing in the opposite directionb. a cooling effectc. a magnetic field at right angles to the currentd. a magnetic field parallel to the electric currentB.2.2

41. Which of the following definitions most closely defines Ohm's law?a. the potential differences in a circuit =1b. the current in a circuit is proportional to the potential difference across itc. the magnetic field produced by a current is proportional to the magnitude of the currentd. the frequency of an AC system is determined by its inductanceE.15

V=IR


42. What is the symbol for electric current?a. Ib. Cc. Ld. FE.14

43. The resistance of a direct current circuit is equivalent to which quantity in an alternating current circuit?a. inductive reactanceb. impedancec. reluctanced. conductivityE.15,18


44. Which NDT method below cannot be used to estimate crack depth?a. alternating current potential drop (ACPD)b. time-of-flight ultrasonicsc. alternating current field measurementd. dye penetrant inspectionA.S-9,253

45. Variations in scanning speed:a. could influence the detection of small discontinuitiesb. will change the amplitude of small discontinuitiesc. will have no direct effect on resultsd. both a and bF.7


46. For which of the following inspection requirements could you not normally use alternating current field measurement for discontinuity detection?a. fatigue cracks in welded joints of high strength steelb. subsurface cracks in welded joints of mild steelc. inspection for cracks in a weld of high strength steel under an epoxy paintcoatingd. surface fatigue cracks in mild steel weldsA.248,252-258

47. IACS is the recognized abbreviation for:a. International Annealed Copper Standardb. Induced Alternating Current Systemc. Inductively Activated Comparison Systemd. Internal Applied Current SystemB.2.15/E.57


48. When alternating current field measurement test coils are wound to formsmall diameter coils, what would they normally be used to detect?a. gradual changes in crack lengthb. gradual changes in crack depthc. small surface discontinuitiesd. changes in permeabilityA.255

49. What term is used to describe the variation in the Bx display as the distance from the surface being tested to the coil varies?a. phase changeb. fill factorc. edge effectd. lift-offA.252


50. Alternating current field measurement cannot be used to inspect:a. steelb. aluminumc. woodd. copperA.248-249


Recalling the mistakes


ACFM Level II Q&A

TWO


Answers to ACFM Level II1.d 2.a 3.b 4.d 5.d 6.b 7.a 8.d 9.b 10.c 11.b 12.c 13.a 14.c 15.d 16.a 17.d 18.b 19.c 20.a 21.a 22.a 23.d 24.c 25.a 26.b 27.c 28.a 29.d 30.d 31.a 32.d 33.a 34.c


1. The Bz, magnetic field can best be described as:a. magnetism perpendicular to the plate surfaceb. perpendicular to the current flowc. produced by curvature of the currentd. all of the aboveA.251

Bz

Bz


2. The Bx, magnetic field is best described as:a. magnetism parallel to the plate surfaceb. 90° to the longitudinal weldc. parallel to the electrical currentd. zeroA.251

3. If the Bx chart recorder trace is low on the graph:a. there is a high current densityb. there is a low current densityc. the electric current is highd. the Bx flux density is highA.251


4. If a current is flowing in a surface (called the x-y plane), then:a. the magnetic flux density in the x direction is proportional to the current in the y directionb. the magnetic flux density in the y direction is proportional to the current in the x directionc. the magnetic flux density in the z direction (out of the x-y plane) isproportional to the curvature of the current in the x-y planed. all of the aboveA.251


5. When measuring the length of a crack with alternating current fieldmeasurement, why can you not use the length between the Bz positive and the Bz negative positions?

a. this is not the true length of the crackb. the Bz locations are produced by circular current flow and will produce Bz

locations just inside the length of the crackc. this size will be smaller than that given by the AC field measurement

programd. all of the aboveF.8

L?


6. For accurate sizing, why must the length to depth ratio of a crack being measured be at least 2:1?a. below this ratio more current would flow to the bottom of the crack thanaround the endsb. below this ratio more current would flow around the ends of the crack than to the bottomc. electricity will follow the path of greatest resistanced. no current will flowA.257-258

7. What electrical property has the greatest effect on the depth of penetration?a. permeabilityb. resistancec. voltaged. Conductivity δ = (πfμσ) -½D.319


8. "What are the disadvantages when using ACPD?a. it cannot be used on paintb. it requires a very clean surface for the injection prods to make contactc. it requires a very clean surface for the potential difference prods to makecontactd. all of the aboveA.248

9. The axes of the coils used to measure the magnetic fields at the surface of a plate are mounted:a. perpendicular to the Bx and Bz fieldsb. parallel to the Bx and Bz fieldsc. in the same directiond. transverse to the direction of the crackA.251


10. If alternating current field measurement is to be used to inspect through anonconductive coating, what is the recommended maximum thickness of thecoating to still ensure detection of a 2 mm (0.08 in.) deep discontinuity?a. 0.1 mm (0.004 in.)b. 1 mm (0.04 in.)c. 5 mm (0.196 in.)d. 25 mm (0.98 in.)A.254

11. If corrosion is present on the surface to be inspected, producing heavy pitting, what effect could it have on the inspection results?a. noneb. there will be reduced sensitivity to small cracks and accuracy of sizingc. a small amount of surface noise could be producedd. the depth of the corrosion pits could be measuredA.266


FIGURE 7. Coating thickness at which magnetic flux density Bx amplitude drops to 1 percent for solenoid probes of three sizes.

A.254


12. What is the effect of lift-off on a differential probe?a. one coil is affected and the other is notb. none of the coils is affectedc. one coil changes positive and the other changes negative, thus cancelling each other (wound oppositely)d. a large signal is produced0.316

13. What will happen if an absolute coil is brought close to the edge of a platea. there will be a significant effect on the displayb. there will be no effectc. the current will change directiond. the magnetic field will change direction0.319


14. What effect will produce a reduced apparent crack depth when usingalternating current field measurement?a. a paint coatingb. a corroded surfacec. a crack, which has line contacts across itd. a material of varying thicknessA.265-266

15. If an indication has been produced by excessive grinding, how can it bedifferentiated from a crack?a. carry out a transverse scanb. increase the speed of the scanc. increase the gaind. carry out parallel scans away from the WeldF.3


16. Which of the following has no effect on crack sizing when using the alternating current field measurement technique?a. size of the slots in the test blockb. multiple crackingc. an inclined crackd. line contactsF.5


17. A large transverse crack in a weld may be indicated during longitudinal scanning by:a. a positive and negative Bz signal with no change in Bxb. a drop in the value of the Bx signal with no change in the Bz signalc. a longitudinal scan will not detect a transverse discontinuityd. a rise in the Bx with a peak and a trough in the BzF.3



Current flow


8.9 Crack Geometry Effects:8.9.4 Transverse discontinuities—if a transverse discontinuity occurs duringthe scan for longitudinal discontinuities then the Bx may rise instead of fallingand the Bz signal will remain the same as for a short longitudinal discontinuity.The X-Y plot will then go upwards instead of down in the representative plotof Fig. 2. This flux leakage effect is, however, related to the opening of thediscontinuity, so it may not be seen for tightly closed discontinuities. Toconfirm the presence of transverse discontinuities, further scans should bemade with the probe orientated to give an induced field perpendicular to theweld, or through use of an array probe with twin fields.

FIG. 2 Example X-Y Plot Produced by Plotting the Bx (vertical) and Bz(horizontal) Together (The orientation of the plot may differ depending upon the instrumentation.)

Bx

Bz


18. The method of crack depth sizing used with alternating current fieldmeasurement corresponds most closely to which of tbe following?a. calibration against test blocks containing slotsb. comparison with predetermined mathematical modelsc. calibration against lift -offd. multiplication of crack length valuesA.250

19. A signal is suspected to have come from a weld repair in the toe of the weld. What procedure(s) should be carried out?a. scan at right angles to the suspect area and the scan will be different from that of a crackb. scan over the repair in order to produce smaller Bz signalsc. scan over the repair in order to produce signals that will cover a wider aread. all of the aboveF.3


20. What is the value of the Bz, magnetic field when a uniform field is appliedto a flat surface of ferritic steel?a. zerob. less than the uniform fieldc. greater than the uniform fieldd. equal to the uniform fieldA.251

21. Which of the following is a limitation of crack sizing by AC field measurement?a. crack length is less than twice the depthb. crack length is less than 10 mm (0.39 in.)c. crack depth is greater than 10 mm (0.39 in.)d. crack depth is greater than tbe depth of penetrationA.253,258


22. When tbe permeability of a material is increased, the depth of penetration does which of the following?a. decreasesb. remains constantc. becomes less inductived. increasesD.318-319

23. "What is the dominant electromagnetic property of a ferromagnetic material?a. low conductivityb. low electrical resistancec. low frequency constantd. high permeabilityD.319


24. High and low current density results in a different distribution in the linesof flux. The number of lines in a unit area is defined as:a. magnetic couplingb. magnetic densityc. flux densityd. hysteresis densityE.43

25. Which of the following frequencies will provide the greatest alternatingcurrent field measurement penetration in aluminum?a. 300Hzb. 10kHzc. 1kHzd. 3kHzD.318


26. The coercive force of a permanent magnet would be_____ the coercive force of a soft iron electromagnetic core.a. less thanb. greater thanc. twiced. equal toH.175

27. It is believed that an AC field measurement instrument is operating defectively. What is the proper course of action?a. all of the rejected material should be retestedb. all of the accepted material should be re testedc. all material should be retested from the time of the last function's test-blocktestd. none of the aboveF.6


28. What is the coupling medium between a coated metal surface and an alternating current field measurement probe when operating under water?a. magnetic fieldb. sea waterc. electric currentd. noneF.2

29. Which of the following statements is incorrect?a. the resistance in a circuit affects the current through the circuitb. the magnetic field produced by a current is proportional to the magnitude of the currentc. a varying magnetic field can produce a current in a conductord. the conductivity of a metal is proportional to the applied magneticfieldB.2.16


30. Which of the following material properties governs the total flux in a magnetic circuit?a. the hardnessb. the resistancec. the conductivityd. the reluctance Ф=NI/S0.319

31. An eddy current is a circulating electrical current induced in a conducting material by:a. an alternating magnetic fieldb. a piezoelectric forcec. X-raysd. none of the above0.315


32. Alternating current field measurement would have the deepest depth ofpenetration in which of the following materials?a. 90-10 Cu/Nib. mild steelc. aluminurnd. stainless steelD.318

33. What generates a magnetic field perpendicular to the surface?a. uniform surface currentsb. increasing surface currentsc. curvature in the surface currents (generate Bz; peak & trough)d. decreasing surface currentsA.251


34. When scanning into tight geometry:a. the Bx signal will decreaseb. the Bz signal will decreasec. the Bx signal will increased. the Bz signal will increaseF.3


ACFM Level III Q&A

Three


Answers to ACFM Level III1.a 2.d 3.b 4.d 5.a 6.b 7.c8.a 9.b 10.c 11.d 12.a 13.b 14.d


1. In an alternating current field measurement technique system, a calibrationstandard may be used to:a. ensure repeatability and reliability of the setupb. calibrate the precise depth of detectable discontinuitiesc. both a and bd. measure the test frequencyF.5

2. Skin effect causes eddy currents to tend to flow near the surface of the test piece. Which of the following factors alter the skin effect?a. testing frequencyb. test piece temperaturec. test piece hardnessd. all of the aboveA.211


3. Which of the following is not a common undesirable effect on the test coil caused by the testing environment?a. temperature variationb. crack in the test samplec. test object making contact with the test coild. foreign object in the test coil fielde. test coil vibrationC.21-25

4. In many cases, AC field measurement can be reliably applied:a. underwaterb. via remotely operated vehiclesc. on railroad car axlesd. all of the aboveA.260-261


5. For AC field measurement discontinuity sizing techniques using standardtheoretical models to produce the sizing tables, what is the commonassumption?a. the input current is unidirectional and of uniform densityb. the input current is omni-directional with varying densityc. all discontinuities are axial surface cracksd. all discontinuities are subsurface cracksA.257-258

6. The reliability, as well as the ability, of AC field measurement to detectdiscontinuities has been specifically determined by:a. railroad cars and tracks not failing for years after AC field measurementexaminationsb. extensive trials carried out on realistic discontinuities under controlled conditionsc. the number of satisfied customers around the worldd. repeated field use around the worldA.260


7. A large, uniform input field in AC field measurement means:a. an improved focal point for localized detectionb. increased ease of discontinuity sizingc. that the current perturbation from a discontinuity extends some distanceaway from the line of a discontinuityd. an increased probability of detectionA.262


Current Perturbation

http://www.ndt.net/article/v05n03/topp/topp.htm


8. It is reasonable to expect that a discontinuity will be detected by AC fieldmeasurement if the Bx signal amplitude is:a. 1 percent or moreb. 10 percent or morec. 80 percent or mored. the Bx signal has no influence on detectionA.263

9. For AC field measurement inspections, probe/solenoid size:a. has no effect on the examination resultsb. should be a consideration while developing a successful AC fieldmeasurement techniquec. is important only for underwater examinationsd. all AC field measurement probes/solenoids are built the sameA.263


10. The false call rate for AC field measurement is:a. normally highb. very dependent on the underwater depthc. generally lowd. greater than all other NDT techniquesA.264

11. While performing AC field measurement, one material where particular care has to be used to avoid false calls is:a. A-214 CSb. A-179 CSc. 304 ssd. duplex steelA.264


12. AC field measurement was originally designed for the detection and sizing of:a. fatigue cracksb. weld burstsc. intergranular attack (IGA) d. conductivity variationsA.265


13. Stress corrosion cracking (SCC) can form a dose series of cracks actingas a "colony“ or clusters of cracks. In these cases, as the signal responsefrom AC field measurement can “superimpose” individual discontinuity signals on close neighboring discontinuity signals, which of the following statements is most correct?a. there is no reliable method for detection and sizing of SCC using ACfield measurementb. in general, AC field measurement is a reliable method for detection anddepth sizing of SCCc. AC field measurement can detect SCC but sizing models· are extremelyinaccurated. special calibration standards must be used when SCC is expected orencounteredA.265


14. With AC field measurement, a corrosion pit can look like a shallow crackon the initial scan. What could be an AC field measurement method fordifferentiating a crack from a pit?a. there is no reliable way to differentiate a crack from a pit using AC fieldmeasurementb. apply a mag-bias AC field measurement probec. review the previous examination reportd. scan the signal with different orientations of the interrogating signal; a pit will produce the same response regardless of probe/currentorientationA.266


Eddy Current Testing


Eddy Current Testing Level I Q&A


Answers to Eddy Current Testing Level I1.d 2.b 3.c 4.b 5.a 6.a7.b 8.d 9.b 10.d 11.d 12.b 13.a 14.c 15.c 16.b 17.b 18.d 19.a 20.b 21.a 22.d 23.b 24.c 25.d 26.a 27.d 28.b 29.d 30.d 31.b 32.a 33.d 34.a 35.b36.b 37.c 38.d 39.b 40.a 41.b 42.b 43.c 44.b 45.d 46.b 47.d 48.d 49.a 50.b 51.a 52.c53.b 54.c 55.b 56.a 57.d 58.a 59.d60.c 61.b 62.a 63.d 64.c 65.d 66.a67.b 68.c 69.a 70.a 71.b 72.c 73.c 74.b 75.d76.b 77.a 78.a 79.c 80.c 81.d 82.d 83.d 84.b 85.d86.d 87.c 88.c 89.a 90.c 91.b 92.c 93.d94.c 95.c 96.b


1. In an electromagnetic testing situation, which of the following can providesources of noise?a. geometrical changesb. permeability variations within the test objectc. electrical interferenced. all of the aboveB.7.26

2. The ratio of the response or amplitude from signals of interest to the response or amplitude of indications that contain no useful information for the test being conducted is referred to as:a. Poisson's ratiob. Signal to noise ratioc. the conductivity to permeability ratiod. the reactance to resistance ratioE.24


3. Which of the following is not a basic component of an eddy current testsystem?a. amplifierb. sine wave generatorc. couplantd. filterB.4.6

4. When conducting an eddy current test using a differential comparison coilarrangement that compares an external reference standard with the testspecimen, the system should be nulled or balanced:a. with only the reference standard in one coilb. with the reference standard in one coil and an acceptable test specimen in the other coilc. with the reference standard in one coil and an unacceptable test specimen in the other coild. with only the test specimen in one coilE.35


5. The impedance of a test coil will increase if the: (XL=2πfL)a. test frequency increasesb. inductive reactance of the coil decreasesc. inductance of the coil decreasesd. resistance of the coil decreasesB.1.22

6. Some of the products commonly tested using encircling coils are:a. rods, tubes and wireb. plate when volumetrically inspectedc. sheets and metalized foild. all of the aboveB.3.9/D.9/H.40.1


7. Which of the following would normally be considered the best ftill factorwhen testing straight tubing with an encircling or feedthrough coil?a. 1.75 (175%)b. 0.95 (95%)c. 0.50 (50%)d. 0.25 (25%)C.47

8. When a metal part is placed in an eddy current test coil, the impedance ofthe coil will be changed by which of the following properties of the part?a. conductivity (electric factor)b. dimensions (magnetic factor)c.permeability (magnetic factor)d. all of the aboveC.67


9. An eddy current test makes use of electrical current induced in a conductive article by:a. gamma raysb. an alternating magnetic fieldc. a piezoelectric forced. all of the aboveC.11/G(Vol. 1).1.25

10. The conductivity of a material can be altered by changing the:a alloy of the specimenb. heat treatment of the specimenc. temperature of the specimend. all of the aboveB.5.2/E.58


11. The depth to which eddy currents are induced in the material will be determined by the:a. conductivity of the materialb. permeability of the materialc. geometrical shape of the material (FOM, figure of merit?) d. all of the above δ = (2/ωμσ)½ = (πfμσ) -½8.2.18/0.3

12. When testing plate with a probe coil, it is noted that the eddy current output indication varies as the distance from the coil to the surface of the test part varies. The term used to describe this action is:a. fill factorb. lift-offc. phase differentiationd. edge effectE.89


12. When testing plate with a probe coil, it is noted that the eddy current output indication varies as the distance from the coil to the surface of the test part varies. The term used to describe this action is:a. fill factorb. lift-offc. phase differentiationd. edge effectE.89

13. The main purpose for spring-loaded eddy current probe coils is to:a. minimize lift -off variationsb. minimize wear on the probec. reduce operator fatigued. eliminate edge effectB.3.2


14. Lift-off is utilized in:a. measuring permeability changesb. measuring conductivity changesc. measuring the thickness of non conductive coatingsd. determining proper test frequencyB.5.13

15. In eddy current test systems where encircling coils are used, couplingefficiency is referred to as:a. lift-offb. edge effectc. fill factord. phase differentiationC.45


16. When inspecting products with a uniform cross section, an eddy currentsignal is produced when the leading end or trailing end of the productapproaches the test coil. This phenomenon is referred to as:a. lift -offb. end effectc. fill factord. phase discriminationE.62


17. Which of the following conditions would be the most difficult to detectwhen eddy current testing a rod with an encircling coil?a. a deep surface crack that has a depth of 30% of the rod diameterb. a small inclusion in the center of the rodc. a 5% change in diameterd. a 10% change in conductivityB.5.13-14

18. When testing tubing with a bobbin coil, most of the eddy currents:a. flow in a longitudinal direction down the tubingb. flow radially in the tubec. flow around only the outside diameter of the tubingd. flow around the inside diameter of the tubingE.32


19. Which of the following test frequencies would produce eddy currents with the largest depth of penetration?a. 100Hz δ = (2/ωμσ)½ = (πfμσ) -½b. 10kHzc. 1 MHzd. l0MHzC.43

20. A test coil's opposition to the flow of alternating current, causing the current to Jag behind the voltage, is called:a. resistanceb. inductive reactance (current lag voltage by π/2 or 90º)c. impedanced. capacitive reactanceB.1.14,17


Inductive reactance (XL) in terms of frequency and inductance is given by:

XL = ω∙L = 2πf∙L

Similarly the Capacitance Reactance:

XC = 1/(ω∙C) = 1/ (2πf ∙C)Inductive reactance is directly proportional to frequency, and its graph, plotted against frequency (ƒ) is a straight line. Capacitive reactance is inversely proportional to frequency, and its graph, plotted against ƒ is a curve.

These two quantities are shown, together with R, plotted against ƒ in Fig 9.2.1 It can be seen from this diagram that where XC and XL intersect, they are equal and so a graph of (XL − XC ) must be zero at this point on the frequency axis.

http://www.learnabout-electronics.org/ac_theory/lcr_series_92.php


Capacitor circuit:Current lead voltage by 90o

Inductor circuit:Current lagging voltage by 90o


21. An increase in the impedance (Z) of a test coil will:a. produce an increase in the voltage through the test coilb. cause a decrease in the measured voltage across the test coilc. not affect the voltage in the test coild. decrease the voltage applied to the coil (V=IZ?)C.32


22. Which of the following will affect the impedance of a test probe?a. conductivity of a test specimen in the coilb. permeability of a test specimen in the coilc. fill factord. all of the aboveB.2.11,34


23. When a test coil consists of a double winding arrangement and onewinding is referred to as a primary winding, the other winding is referred to asthe:a. absolute windingb. secondary windingc. phase windingd. none of the aboveB.3.16

24. Large diameter surface scanning coils would most likely be used for tbedetection of:a. pittingb. small inclusionsc. changes in conductivityd. porosityA.136/G(Vol. 11).1.32


25. Small diameter probe coils would typically be used for tbe detection of:a. slow changes in dimensionsb. gradual changes in conductivityc. variation in heat treatmentd. small surface discontinuitiesC.54/G(Vol. 11).1.32

26. Direct current saturation coils would most likely be used when testing:a. steelb. aluminumc. copperd. brassB.2.13-14


27. An absolute coil arrangement can be used in:a. encircling coils onlyb. probe coils onlyc. probe and encircling coils onlyd. probe, encircling and inside diameter coilsB.3.11

28. Which of the following expresses the primary purpose( s) of thesecondary winding(s) in an eddy current coil ?a. induce eddy currents in the test specimenb. detect changes in the eddy current flowc. induce eddy currents in the test specimen and detect changes in the eddy current flowd. provide DC saturationB.3.16


29. Which of the following eddy current test coil arrangements uses one areaof the test specimen as a reference standard against which another area onthe same specimen is simultaneously compared?a. single absolute coilb. double absolute coilc. DC saturation coild. differential coilB.3.13


30. Reference standards used for electromagnetic testing:a. must contain artificial discontinuities such as notches and drilled holesb. must contain natural discontinuities such as cracks and inclusionsc. must be free of measurable discontinuitiesd. may contain artificial or natural discontinuities or be free ofdiscontinuities depending on the test system and the type of test beingconducted8.6.7-9

31. A reference standard used to ensure that the amplitnde and phasecharacteristics of a test system do not drift during continuous testing is calleda:a. DGS standardb. calibration standardc. reference blockd. none of the above8.7.26


32. Which of the following could not be tested by the eddy current testingmethod?a. a 102 mm (4 in.) thick plate to be tested for small discontinuitiesthroughout the plateb. tubing to be tested for surface cracksc. rod to be tested for laps and seamsd. tubing to be tested for variations in outside diameterB.2.20

33. Which of the following is not true about an eddy current test?a. it can be used for high-speed testingb. it can accurately measure conductivityc. it can be set up to provide high sensitivity to small discontinuitiesd. it can penetrate up to 152 mm (6 in.) in a test partB.2.20


34. The entire cross-sectional area of a tube can be evaluated at one time when using:a. an encircling coilb. a probe coilc. a secondary windingd. none of the aboveB.3.9

35. When attempting to determine the exact circumferential location of a discontinuity in a tube, the test system should include:a. a phase shifterb. a probe coilc. an attenuatord. a penetrameterC.54


36. It is often possible to sort various non ferromagnetic alloys of a metal bymeans of an eddy current test when:a. there is a unique range of permeability values for each alloyb. there is a unique range of conductivity values for each alloyc. the direction of induced eddy currents varies for each alloyd. the magnetic domains for each alloy are differentE.69

37. Which of the following products would be most applicable to a test using an inside coil?a. sheetb. rodc. bolt holed. coating thicknesses6.3.2


38. When eddy current testing rod for discontinuities, which of the following conditions could produce extraneous indications? a. improper adjustment of the hold-down rollers used to center the rod in the coilb. feeding rod through the coil at an excessive speedc. changes in dimensiond. all of the abovee. none of the aboveE.24

39. One method of reducing non relevant indications when eddy current testing ferromagnetic materials is to:a. decrease the pressure on the hold-down rollersb. use a direct current saturation coil to magnetically saturate the test specimenc. readjust the gain controld. increase the rate of feed through in the coilE.62


40. In order to generate measurable eddy currents in a test specimen, the specimen must be:a. a conductorb. an insulatorc. either a conductor or an insulatord. a ferromagnetic material6.2.4

41. When using an encircling coil with both primary and secondary windings, the excitation alternating current is applied to:a. the secondary windingb. the primary windingc. either the primary or secondary winding depending on the setting of an instrument controld. both the primary and secondary coilsE.14


42. Which of the following is not a readout system used to present eddy current test information?a. alarmsb. litmus paperc. cathode ray tubed. digital data storageE.26

43. Which of the following statements best describes the selection of eddy current test frequency?a. the frequency must equal the f/fc ratio to give an accurate testb. the frequency must be within ±3% of the f/fc ratio to give an accurate testc. there is a range of suitable frequencies centered around the optimumfrequencyd. the frequency should be within ±25% of the characteristic frequencyE.83


44. ·Which of the following options would not have the potential to improvethe displayed signal-to-noise ratio of a test?a. change to a test frequency that will decrease the noiseb. increase the amplification of the test instrumentc. improve the fill factord. enable filter functions in the instrumentE.24

45. When conducting an eddy current test on tubing, the magnitude of theindication caused by a discontinuity is dependent on:a. the depth of the discontinuityb. the width of the discontinuityc. the length of the discontinuity (for MFL Amplitude =k∙D/W where D=depth, W=width)?d. all of the aboveE.63


46. A coil's magnetic field may be viewed as a distribution of lines of fluxaround the coil. The number of lines in a unit area is defined as:a. magnetic probabilityb. flux densityc. magnetic couplingd. hysteresis densityB.2.19/E.43

47. Demagnetization is generally needed when the residual field in aspecimen:a. may affect the operation or accuracy of instruments when the specimen isplaced in serviceb. may interfere with the proper functioning of the partc. might cause particles to be attracted and held to the surface of moving partsd. any of the above reasons could make demagnetization necessaryJ.67


48. Eddy current test techniques can be used to:a. measure nonmetallic coating thicknesses on conductorsb. measure cladding thicknesses (metal-to-metal)c. gage the thickness of conductive sheetsd. all of the aboveB.5.13

49. Eddy currents cannot be induced in:a. latex paintb. aluminwnc. steeld. copperE.13


50. Which of the following statements is not true of ferromagnetic materials?a. they have permeability values much greater than Ib. they do not exhibit any magnetic hysteresis characteristicsc. they will have a definite saturation point on a B/H curved. they will exhibit some degree of residual magnetismC.18

51. Eddy currents always travel:a. in circular pathsb. in nonconductive materialsc. radially when testing rod with an encircling coild. in a gasB.2.5


52. For online eddy current inspections in a tubing mill, the effective DCsaturation point of ferromagnetic materials is reached when the currentapplied to the saturation coil is set at a value where for any further increase inthat current, the eddy current signal-to-noise ratio will:a. start to increaseb. start to decreasec. show no significant changed. suddenly drop to zeroB.2.13


53. When sorting on the variation between two distinct alloys, it is desirable tohold all indications within the bounds of the readout device in order to:a. eliminate overloadingb. detect the possible existence of a third alloyc. make proper balancing possibled phase the readings correctlyA.275

54. A term used to define a standardized condition in a device or system which results in zero output is:a. high frequency standardizationb. integrationc. null or balanced. differentiationB.6.19/K.203


55. A term used to describe holes, grooves, notches, etc., that are introduced into a reference standard to provide accurately reproducible quality levels is: a. a natural discontinuityb. an artificial discontinuityc. an ellipsed. none of the aboveB.6.9

56. A term used to define one or more turns or loops of a conductor wound in such a manner as to produce an axial magnetic field when current passes through the conductor is:a. a coilb. a resistorc. a capacitord. an oscillatorB.1.14/C.21


57. Nondestructive tests are commonly conducted to:a. determine the quality of finished productsb. locate defective material before excessive fabrication is performed on the materialc. monitor material production techniques and processesd. all of the aboveA.2/1.7

58. An eddy current coil arrangement that does not make a comparison with either two sections of the test specimen or one section of the test part and a reference standard is called:a. an absolute coil arrangementb. a self-comparison differential coil arrangementc. an external reference differential coil arrangementd. none of the aboveB.3.12


59. Which of the following are common applications for eddy current testing?a. measurement of conductivity or a combination of conductivity andpermeabilityb. measurement of the thickness of thin metal sections cladding or coatingc. detection of surface and subsurface discontinuitiesd. all of the aboveE.91


60. Which of the following is not a primary purpose for using an eddy currentstandard?a. to determine if the eddy current test system is capable of performing thetest properlyb. to determine if a discontinuity is a cause for rejectionc. to determine the instrument control settings needed to pass the highest percentage of test specimens rund. to determine if the sensitivity of a test system has drifted with timeB.6.4


61. Material must be reasonably centered in an encircling test coil of a discontinuity detection system because, even with an acceptable fill factor ratio:a. the coil would otherwise be out of balanceb. parts of the material farthest away from the coil, radially, may receive a less sensitive inspectionc: the flow of eddy currents around the product will be disturbed, resulting inimproper penetrationd. lack of proper centering may change the phase adjustment of theinstrumentB.3.10


62. When you determine that a discontinuity detection instrument has beenset up incorrectly, or is defective, all material:a. should be retested since the time that a correct setup or proper operation was last verifiedb. accepted should be retestedc. rejected should be retestedd. none of the aboveC.61

63. An eddy current system will measure variations caused by differences in:a. size or shapeb. grade or chemistry of the materialc. the way in which the material has been processedd. all of the aboveB.4.8


64. A length of tubing containing a notch of uniform Width and depth runningfrom end to end, when tested with an encircling self-reference differential coilsystem, will produce:a. erratic signalsb. a continuous, sustained signalc. no signal changed. excessive signalsB.3.13

65. In encircling coil eddy current testing, optimum sensitivity to a knowndiscontinuity placed at random on the surface of a nonferrous length of tubingis obtained by:a. proper choice of frequencyb. centering the tubing in the coilc. proper adjustment of phased. all of the aboveD.10


66. One principal advantage of spinning probe eddy current testing is:a. The ability to locate the exact position of discontinuitiesb. its relative insensitivity to permeability variationsc. the variety of internal and surface discontinuities that may be detectedd. all of the aboveC.54


67. At any given instant, a spinning probe eddy current instrument should beinspecting:a. one complete circumference of the productb. an area defined by the size of the probe coilc. one longitudinal line the length of the productd. none of the aboveC.54

68. A spinning probe eddy current instrument would be most useful in:a. measuring the hardness of ferromagnetic steel productsb. discontinuity detection in hexagonal and shaped materialc. detecting and precisely locating surface discontinuitiesd. inspection of copper bus bars for electrical conductivityC. 54


69. In a feed through encircling coil eddy current system, a calibration standard may be used to:a. ensure repeatability and reliability of the setupb. determine the circumferential extent of a discontinuityc. reduce sensitivity to vibrationd. measure the test frequencyC.61

70. What causes phase shift in an eddy current test coil?a. a change in the ratio of inductive reactance (XL) to resistance (R)b. a change in the sensitivity setting of the instrumentc. use of modulation analysisd. none of the aboveC.32


71. In a feedthrough encircling coil discontinuity detection eddy currentsystem, what would be the purpose of running a calibration discontinuityseveral times but in various positions (such as top, bottom, left and right)?a. to check the phase selectivityb. to ensure proper centering of the material in the test coilc. to select the modulation analysis settingd. to select the proper operating speedB.3.10


72. In a feedthrough encircling coil eddy current system, DC saturation wouldprobably be most helpful in testing:a. copper water tubingb. titanium tubingc. ferromagnetic steel tubingd. brass rivet wireB.2.13

73. In an electromagnetic test system, the test frequency is controlled by the:a. oscilloscopeb. sensitivity settingc. oscillator circuitd. modulation analysis settingA.175


7 4. Variations in the chemical composition of a nonferromagnetic alloy would most likely affect its:a. permeabilityb. conductivityc. diameterd. frequencyB.7.5

75. Which of the following frequencies will provide the greatest eddy currentpenetration in aluminum?a. 1kHzb. 10kHzc. 3kHzd. 300HzC.43


76. A symbol commonly used to express conductivity is:a. μb. σc. XLd. RC.Vii/E.57

77. A symbol commonly used to express permeability is:a. μb. σc. XLd. RE.47


78. The method used to generate eddy currents in a test specimen by meansof a coil can most closely be compared with the action of a:a. transformerb. capacitorc. storage batteryd generatorC.36


79. When eddy current testing a nonferrous specimen, a discontinuity will:a. increase the effective conductivity of the specimenb. increase the effective permeability of the specimenc. decrease the effective conductivity of the specimend. none of the aboveD.25

Comments: The presence of crack, decrease the effective conductivity of the specimen by the presence of break (discontinuity), reducing the eddy current flow; generating less secondary magnetic field that interact with the exciting/pick-up coil. The resistance component will decrease and the inductive reactance will increase as less energy is taken away from the exciting coil.

Decrease effective conductivity of specimen Decrease effective resistance of exciting coil Increase inductive reactance of exciting coil


If the eddy current circuit is balanced in air and then placed on a piece of aluminum, the resistance component will increase (eddy currents are being generated in the aluminum and this takes energy away from the coil, which shows up as resistance) and the inductive reactance of the coil decreases (the magnetic field created by the eddy currents opposes the coil's magnetic field and the net effect is a weaker magnetic field to produce inductance). If a crack is present in the material, fewer eddy currents will be able to form and the resistance will go back down and the inductive reactance will go back up. Changes in conductivity will cause the eddy current signal to change in a different way.


80. In multifrequency tubing inspection applications, signal analysis is most often performed using:a. phase angle analysis onlyb. signal amplitude analysis onlyc. a careful correlation of both amplitude and phase informationd. the ellipse methodB.86

81. When testing tubes with an ID bobbin probe:a. low voltage signals indicate insignificant discontinuity depthsb. high voltage signals are always from rejectable discontinuitiesc. signals from support plates always hide discontinuity signalsd. none of the above is trueA.403


82. A multicoil array probe used in a surface scanning application:a. should improve detection of localized discontinuitiesb. can cover a large surface area in one passc. might increase the complexity of signal detection and interpretationd. all of the aboveB.8.14

83. Data from the external-reference differential channels of ID bobbin probedata can be used to detect:a. long, gradually tapering discontinuitiesb. one-sided erosionc. temperature differencesd. all of the aboveD.14


84. Self-comparison differential channels would be best for the detection of:a. long tapered discontinuitiesb. short abrupt discontinuitiesc. temperature differencesd. all of the aboveB.3.13

85. Which of the following affects the characteristics of the primary coil in an eddy current system?a. the presence of a crackb. the presence of an edgec. change in material propertiesd. all of the aboveF.320


86. Which of the following is applicable to eddy current testing?a. it can be used to provide high sensitivity to small discontinuitiesb. it can be used for high-speed testingc. it can be used to measure coating thicknessesd. all of the aboveF.314

87. A secondary magnetic field produced by eddy currents induced in a nonmagnetic conductor close to the inducing coils:a. induces a magnetic field parallel to the surfaceb. aids the coil's magnetic fieldc. opposes the coil's magnetic fieldd. decreases the frequency of the currentF.319


88. A test specimen used as a basis for calibrating test equipment or as acomparison when evaluating test results is referred to as a:a. null-balancerb. phase shifterc. reference standardd. high pass filterB.6.4/H.40.5

31. A reference standard used to ensure that the amplitnde and phasecharacteristics of a test system do not drift during continuous testing is calleda:a. DGS standardb. calibration standardc. reference blockd. none of the above8.7.26


89. The process of comparing the reading or output of an instrument, deviceor dial with a standard to determine the instrument's accuracy, capacity orgraduations is referred to as:a. calibrationb. differentiationc. integrationd. phase shiftingG(Vol. 11).2.13

90. Figure 1 is an illustration of a material's:a. phase analysis loopb. sine wavec. hysteresis loopd. none of the aboveC.19/H.33.3


91. Ferromagnetic materials that have been magnetically saturated tosuppress permeability variations may retain a certain amount of themagnetization. This is called:a. coercive forceb. residual magnetismc. hysteresis loopd. hysteresis lossC.17-18

92. An alternating current flowing in a conductor will set up:a. an alternating current field around the conductorb. a periodically changing voltage tangent to the conductorc. an alternating magnetic field around the conductord. none of the aboveB.2.4


93. The characteristics of the alternating magnetic field in the vicinity of the AC coil are affected by:a. the coil parametersb. the magnitude of the applied AC currentc. the frequency of the applied AC currentd. all of the aboveI.346


94. The region around a magnet that attracts other pieces of iron or steel is called:a. amaxwellb. retentivityc. the magnetic fieldd. alternating currentH.30.2

95. Testing that requires that the test article be loaded and/or sectioned to verify and/or establish mechanical or physical properties is known as:a. impedance testingb. phase analysis testingc. destructive testingd. nondestructive testingH.4.1


96. The depth of penetration would ____ if the localized permeability ofa material increased.a. increaseb. decreasec. remain constantd. increase the conductivity8.2.22


Eddy Current Testing Level II Q&A

TWO


Answers to Eddy Current Testing Level II1.a 2.d 3.a 4.b 5.d 6.a 7.d 8.a 9.c 10.c 11.b 12.a 13.c 14.d 15.d 16.b 17.b 18.c 19.d 20.b 21.b 22.a 23.c 24.d 25.b 26.c 27.b 28.c 29.c 30.a 31.d 32.d 33.b 34.c 35.a 36.b 37.a 38.d 39.c 40.a 41.d 42.b 43d 44.c 45.c 46.d 47.d 48.b 49.b 50.d 51.a 52.d 53.b 54.d 55.c 56.b 57.b 58.a 59.d60.a 61.a 62.c 63.c 64.c 65.a 66.a 67.c 68.a 69.b 70.d 71.b 72.a 73.b 74.a 75.c 76.c 77.d 78.a 79.a 80.c 81.a 82.a 83.b 84.c 85.d86.d 87.b 88.c


1. A method of minimizing the effect of indications caused by gradual dimensional changes while retaining the indications caused by discontinuities is to: a. enable a high-pass filter in the eddy current test equipmentb. enable a low-pass filter in the eddy current test equipmentc. increase the band pass of the amplifierd. use the impedance method of testingA.29,186

2. Which of the following methods may be used to improve the signal-to-noise ratio of an electromagnetic testing system?a. filtering or differentiationb. phase discriminationc. integrationd. all of the aboveA.173


3. In order to decrease the effect on conductivity readings due to variations intest part thickness:a. the test frequency should be increasedb. the test frequency should be decreasedc. the fill factor should be decreasedd. there is no practical method fordecreasing this effectA.54

4. When testing by the eddy current method, discontinuities will be most easily detected when the eddy currents are:a. coplanar with the major plane of the discontinuityb. perpendicular to the major plane of the discontinuityc. parallel to the major plane of the discontinuityd. 90 degrees out of phase with the current in the coilD.25/E.32


5. A term used to describe the effect observed due to a change in the electromagnetic coupling between a test specimen and a probe coil when the distance of separation between them is varied is:a. fill factorb. edge effectc. end effectd. lift-offA.130,324

6. A term used to define the phenomenon where, at very high frequencies, the eddy current flow is restricted to an extremely thin outer layer of the conductor is: a. skin effectb. high-frequency filtrationc. low-frequency filtrationd. any one of the aboveA.131jD.23/K.8


7. The fill factor when a 13 mm (0.5 in.) diameter bar is inserted in a 25 mm (I in.) diameter coil is:a. 0.5 (50%)b. 0.75 (75%)c. 1.0 (100%) [(D1/D2)2 , (.5/1)2 = 0.25]d. 0.25 (25%)D.24/E.89

8. Which of the following could be used to suppress unwanted high-frequencyharmonics?a. low-pass filterb. oscillatorc. phase discriminatord. high-pass filterA.186


9.The impedance change of an eddy current test coil due to a change in test part characteristics can be most easily analyzed as a combined change in: a. capacitive reactance and resistanceb. harmonic frequencies and inductive reactancec. signal amplitude and phased. retentivity and harmonic frequenciesE.65


10. The inductive reactance of a test coil can be calculated using the formula:a. XL= 2πLb. XL = 0.5 π Lc. XL= 2πfLd. X1.= IRE.18/H.36.1

(XL=ωL = 2πfL)


11. When conducting, an electromagnetic test, variations in the test material can be detected as variations in:a. test speedb. impedance of a pickup coilc. none of the aboved. both a and bA. 51-52

12. A term used to define two or more coils electrically connected in opposition such that any electromagnetic condition which is not common to both a test specimen and a reference specimen will produce a signal change in the system is: a. differentialb. Absolute (absolute, differential, reflection)c. laminard. flying probesA.52,129


13. In a manufacturing environment, tubing is generally inspected using:a. U -shaped coilsb. gap coilsc. encircling coilsd. none of the aboveD.9/E.32

14. When performing a hardness test on small parts with an encircling coil arrangement, which of the following test parameters may be considered important?a. length of the test sampleb. thickness of the test samplec. cross-sectional area of the test sampled. all of the aboveA.74,271

Hardness affects conductivity?


15. In a test coil consisting of both a primary and secondary winding, thevoltage across the secondary is a function of:a. test material permeabilityb. test frequencyc. geometry of the test objectd. all of the aboveD.28

16. Eddy current testing relies on the principle of:a. magnetostrictionb. electromagnetic inductionc. piezoelectric energy conversiond. magnetomotive force (Ф= NI/S, F=NI)A.28,33


17. When the H field strength around a ferromagnetic material is increased and then decreased to zero, the induced field B within the part does not return to zero. The term to define this B value when H has returned to zero is:a. coercive forceb. residual magnetismc. saturation valued. hysteresis lossA.48

18. The three major specimen parameters that influence eddy current testing are:a. electrical conductivity, frequency andmaterial geometryb. density, permeability and frequencyc. electrical conductivity, permeabilityand material geometryd. thermal conductivity, electricalconductivity and permeabilityE. 57


19. Doubling the number of turns on a coil will:a. double the inductanceb. halve the inductance (L= μoN2A/L)c. decrease the inductance by a factor of fourd. increase the inductance by a factor of fourD.15/E.13

20. The frequency ratio f/fg can be defined as:a. the argument of the mathematical function describing theelectromagnetic field within the test specimenb. test frequency divided by limit frequencyc. neither a nor bd. both a and bD.28/E.85


21. When testing tubing using an encircling coil, what is the phase relationship of the output signals from identical ID and OD discontinuities?a. the signals are in phaseb. the phase of the OD discontinuity leads the phase of the ID discontinuityc. the phase of the OD discontinuity lags the phase of the ID discontinuityd. indeterminateE.86

22. A term used to define an instrumentation technique that discriminates between variables in the test part by the phase angle response differences seen on the output device is:a. phase analysisb. phase distortionc. phase shiftingd. phase discriminationA.472/E.65,142


23. If the characteristic frequency (fg) of a material is 125 Hz, the test frequency required to give an f/fg ratio of 10 wouldbe:a. 1.25 Hzb. 12.5 Hzc. 1.25 kHzd. 12.5 kHzE.85


24. At a fixed test frequency, in which of the following materials will the eddy current penetration be greatest?a. aluminum (35% IACS)b. brass (15% IACS)c. copper (95% IACS)d. lead (7% IACS)E.84


25. If the test frequency increases while the field strength is held constant, the surface eddy current density:a. decreasesb. increasesc. remains the samed. could do any of the aboveE.83-84

26. As the fill factor decreases, the impedance variation of a pickup coil produced by a given change in conductivity will:a. increaseb. remain the samec. decreased. could do any of the aboveA.130


27. The abscissa values on the impedance plane shown in Figure 2 are given in terms of:a. absolute conductivityb. normalized resistancec. absolute inductanced. normalized inductanceD.29

ωLo = Inductive reactance of free space


28. In Figure 2 (an impedance diagram for solid nonmagnetic rod), the fg orcharacteristic frequency is calculated by the formula:a. fg = σμ /d2

b. fg = δμ/d2

c. fg = 5066/σμrd2

d. fg = R/L


29. In Figure 2, a change in the f/fg ratio will result in:a. a change in only the magnitude of the voltage across the coilb. a change in only the phase of the voltage across the coilc. a change in both the phase and magnitude of the voltage across thecoild. no change in the phase or magnitude of the voltage across the coilE.86


30. In Figure 3, the solid curves are plots for different values of:a. fill factor (lift-off)b. heat treatmentc. conductivityd. permeability


31. Which of the following would be easier to detect in tubing by the eddy current method using the self-comparison differential coil arrangement? a. gradual changes in diameterb. gradual changes in conductivityc. changes in temperatured. short discontinuitiesA.156


32. Figure 4 illustrates the fact that eddy current responses:a. can be caused by several parametersb. differ in phase and magnitude with different parameter changesc. can be made selective with regard to the variable of interestd. all of the aboveE.57

Charlie C

hong/ Fion Zhang


33. To eliminate any dependence on the number of test coil turns, the inductance values of an impedance diagram are:a. disregardedb. Normalized ( divided by 1/ωLo)c. corrected to a value of 1d. none of the aboveA.137

34. A term used to define a system that indicates only the magnitude ofvariations in the total coil impedance regardless of the phase or direction inwhich it occurs on an impedance plane is:a. inductive reactance magnitude systemb. feedback-controlled systemc. impedance-magnitude systemd. impedance vector analysis systemE.65


35. When eddy current testing tubing with a system that includes adjustablefilter functions, which of the following variables would be classified as a highfrequency variable?a. small discontinuitiesb. conductivity changesc. diameter changesd. wall thickness variationsE.82

36. A major problem for an untrained or inexperienced operator using theeddy current test method is the:a. inability of eddy current testing to accurately measure conductivityb. large number of variables that appear in the output readout mechanismc. need to test at low speeds to prevent skippingd. inability of eddy current testing to detect small discontinuitiesE.11


37. Figure 5 illustrates the fact that the limit frequency (fg) equations and theimpedance diagrams for long solid rods and long thin-walled tubing are:a. differentb. identicalc. similard. unrelatedE.85

Solid rod fg = 5066*/Gd2

Thin wall tube = 5066/GdiWWhat is G?G = μoσ?

*Could be 5060, 5056 or in this case 5066!


37. Figure 5 illustrates the fact that the limit frequency (fg) equations and the impedance diagrams for long solid rods and long thin-walled tubing are:a. differentb. identicalc. similard. unrelatedE.85

Solid rod fg = 5066*/Gd2

Thin wall tube = 5066/GdiWWhat is G?G = μoσ? *Could be 5060, 5056 or in this case 5066!

long solid rods

thin-walled tubing


3.1.2 Limiting Frequency fg of Encircling CoilsEncircling coils are used more frequently than surface-mounted coils. With encircling coils, the degree of filling has a similar effect to clearance with surface-mounted coils.The degree of filling is the ratio of the test material cross-sectional area to the coil cross-sectional area. Figure 3.7 shows the effect of degree of filling on the impedance plane of the encircling coil. For tubes, the limiting frequency [point where ohmic losses of the material are the greatest (and no more?) ] can be calculated precisely from Eq. (3.2 & 3.3):

fg = 5056/(σ∙di∙w∙μr) (3.2)

Where:fg = limiting frequency σ = conductivity di = inner diameter w = wall thickness μr (rel) = relative permeability

For Solid Rod:

fg = 5060/(σ∙μr∙d2) (3.3)

Where:d= solid rod diameter

Introduction to Nondestructive Testing: A Training Guide, Second Edition, by Paul E. Mix


38. When a direct current saturation technique is applied to a ferromagneticmaterial, the flux density in the material is:a. less than the flux density generated by the test coil because of heat lossesb. less than the flux density generated by the test coil because of resistivityc. the same as the flux density generated by the test coild. greater than the flux density generated by the test coilB.2.20/E.101


39. In eddy current testing, the specimen is coupled to the test coil by:a. core couplingb. magnetic saturationc. the coil's magnetic fieldd. magnetic domainsA.51/E.89,136

40. The thickness of non conductive coatings on a conductive base can be most simply measured by:a. observing the lift-off effect caused by the coatingb. testing both sides of the specimenc. varying the current in the test coild. varying the test frequency over a given range during the testA.461


41. The use of magnetic shielding around the exciting coil will generally:a. increase the magnetic field extension but decrease the eddy currentpenetrationb. increase the magnetic field extension and eddy current penetrationc. decrease the magnetic field extension but increase the eddy currentpenetrationd. decrease the magnetic field extension and eddy current penetrationA.139,144

42. Which of the following is not a factor that affects the inductance of an eddy current test coil?a. diameter of the coils Ф= NI/S, F= NI, XL=2πfL, L=μoN2A/Lb. test frequencyc. overall shape of the coilsd. distance from other coilsE.17


43. The formula used to calculate the impedance of an eddy current test coil is:a. Z= 2≠ fLb. Z= XL +Rc. Z=√(XL +R)d. Z= √(X2+R2)E.19

44. An out-of-phase condition between current and voltage:a. can exist only in the primary winding of an eddy current coilb. can exist only in the secondary winding of an eddy current coilc. can exist in both the primary and secondary windings of an eddy current coil (in the pure inductance circuit current lag voltage by 90º)d. exists only in the test specimenA.160


45. A surface coil mounted so that the coil can be rotated about the circumference of a test specimen is known as a(n):a. bobbin coilb. encircling coilc. rotating coild. gap coilE.406


46. An eddy current test coil which uses high permeability material to purposely shape the magnetic field is known as a(n):a. bobbin coilb. encircling coilc. rotating coild. shielded coil (magnetic shielding versus eddy current shielding)A.144


47. The conductivity (σ) value for a metal is a function of the:a. heat treatment given the metalb. cold working performed on the metalc. aging process used on the metald. all of the aboveA.53

48. Which of the following materials would be more likely used to create a holding fixture for a probe coil?a. aluminurnb. plasticc. copperd. steel0.19


49. A term used to define the timing relationships involved in alternatingcurrent signals is:a. magnitudeb. phasec. impedanced. reactanceB.1.16/E.15

50. When eddy current testing a nonferrous material, the choice of mode of operation and test frequency will be affected by the:a. degree of phase discrimination requiredb. eddy current penetration neededc. discontinuity detection and sizing criteriad. all of the abovee. a and b onlyA.403


51. Which of the following coil arrangements would eliminate or decrease theeffects of minor variations in diameter, chemical composition, hardness, etc.,which occur gradually along the length of a wire?a. self-comparison differentialb. external reference absolutec. single coil absoluted. double coil absoluteA.156


52. Which of the following conditions are not valid criteria when selectingspecimens to be used as reference standards?

a. the specimen should be of the same size and shape as the piece to be tested

b. the specimen should have the same heat treatment as the piece to be tested

c. the surface finish of the specimen should be the same as the piece to beTested

d. if the material is aluminum, the surface should always be anodizedA.270


53. An eddy current test coil's magnetic field intensity in air:a. increases with distance outside the coil and varies across the diameter

inside the coilb. decreases with distance outside the coil and varies across the diameter

inside the coilc. decreases with distance outside the coil and is assumed to be

constant across the diameter inside the coild. increases with distance outside the coil and is assumed to be constant

across the diameter inside the coilE.66


54. The circuitry or electronic functions that make it possible to minimize theeffect of signals caused by variables of no interest on the readout mechanism are based on differences in:a. amplitudeb. phasec. frequencyd. any one or a combination of the quantities listed aboveA.174

55. When a nonferromagnetic rod is placed inside an encircling coil:a. the magnetic field generated by the coil is increased in intensityb. the distribution of eddy currents is uniform through the rod's cross sectionc. the distribution of eddy currents is at a maximum at the rod's surface, or near the surface, and decreases to essentially zero at the rod's centerd. the temperature of the rod decreasesE.31


DiscussionSubject: 55. When a nonferromagnetic rod is placed inside an encircling coil:will the magnetic field generated by the coil is decrease and not increased in intensityb. the distribution of eddy currents is uniform through the rod's cross sectionc. the distribution of eddy currents is at a maximum at the rod's surface, or near the surface, and decreases to essentially zero at the rod's centerd. the temperature of the rod decreasesE.31


56. A decrease in conductivity is equivalent to:a. an increase in permeabilityb. an increase in resistivity (σ=1/ρ), ρ= Rl /Ac. a decrease in permeabilityd. a decrease in resistivityA.53/8.2.8

57. When the voltage applied to a circuit and the current through the circuit both reach their maximums and minimums at the same time, the voltage and current are:a. additiveb. in phasec. regeneratived. out of phaseE.15


Conductivity and ResistivityConductivity and resistivity is related as follows:

σ =1/ ρ

Where σ = Conductivity (sigma) and ρ =Resistivity (rho). Conductivity can be quantified in Siemens per m (S/m) or in Aerospace NDT in % lACS(International Annealed Copper Standard). One Siemen is the inverse of an ohm. Another common unit used for conductivity measurement is Siemen per cm (S/cm).


Electrical Conductivity and ResistivityResistance can be defined as follows:R = l /(Aσ) or R = ρl/A

Where:R = the resistance of a uniform cross section conductor in ohms (Ω), l = the length of the conductor in the same linear units as the conductivity or resistivity is quantified, A=Cross Sectional area, σ = conductivity in S/m and ρ = Resistivity in Ω m.


From Eq. (4.3) it can be seen that if the temperature is increased, resistivity increases and conductivity decreases from their ambient temperature levels. Conversely, if temperature is decreased the resistivity decreases and conductivity increases. To convert resistivity values, such as those obtained from Eq. (4.3) to conductivity in terms of% IACS, the conversion formula is,

%IACS = 172.41/ρWhere:IACS = international annealed copper standardρ = resistivity in Ω∙m

ρ100%IACS = 1.724110-8 Ωm = 100% IACS

(4.4)

http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity


3.3.2 Electrical Conductivity and Resistivity

In eddy current testing, instead of describing conductivity in absolute terms, an arbitrary unit has been widely adopted. Because the relative conductivities of metals and alloys vary over a wide range, a conductivity benchmark has been widely used. In 1913, the International Electrochemical Commission established that a specified grade of high purity copper, fully annealed -measuring 1 m long, having a uniform section of 1 mm2 and having a resistance of 1.7241x10-8 ohm-meter at 20°C (100% IACS = 1.7241x10-8

ohm-meter at 20°C) - would be arbitrarily considered 100 percent conductive. The symbol for conductivity is σ and the unit is Siemens per meter. Conductivity is also often expressed as a percentage of the International Annealed Copper Standard (IACS).

Note:100% IACS = 1.7241x10-8 ohm-meter at 20°C


Keywords:

100% IACS – (high purity copper, fully annealed - measuring 1 m long, having a uniform section of 1 mm2 and having a resistance of 1.7241x10-8 ohm-meter at 20°C.

Absolute terms:

Resistivity ρ : 1.7241x10-8 ohm-meter at 20°C.

Conductivity 1/ρ : (1.7241x10-8)-1 /ohm-meter or 5.8001 x 107 Siemens/m at 20°C

Siemens = mho? or (ohm)-1

https://www.nde-ed.org/GeneralResources/IACS/IACS.htm


Electrical Conductivity σElectrical conductivity is a measure of how well a material accommodates the movement of an electric charge. It is the ratio of the current density to the electric field strength. Its SI derived unit is the Siemens per meter (mho/m), but conductivity values are often reported as percent IACS.

IACS is an acronym for International Annealed Copper Standard, which was established by the 1913 International Electrochemical Commission. The conductivity of the annealed copper (5.8001 x 107S/m) ( 1/σ = ρ= 1.724 x 10-8

Ωm) is defined to be 100% IACS at 20°C .

Therefore, iron with a conductivity value of 1.04 x 107 S/m, has a conductivity of approximately 18% of that of annealed copper and this is reported as 18% IACS. An interesting side note is that commercially pure copper products now often have IACS conductivity values greater than 100% IACS because processing techniques have improved since the adoption of the standard in 1913 and more impurities can now be removed from the metal.

https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Physical_Chemical/Electrical.htm


58. Which of the following is not a commonly used eddy current testing readout mechanism?a. signal generatorb. meterc. X-Y displayd. strip-chart recorderA.174

59. Which of the following materials would have the highest resistivity value?a. aluminum with a 42% IACS ratingb. magnesium with a 37% IACS rating %IACS ∝ 1/ρc. cast steel with a 10.7% IACS ratingd. zirconium with a 3.4% IACS ratingA.53


60. The magnetic field generated by eddy currents induced in a test specimen:a. opposes the magnetic field that induced the eddy currentsb. reinforces the magnetic field that induced the eddy currentsc. cancels the magnetic field that induced the eddy currentsd. has no effect on the magnetic field that induced the eddy currentsA. 51

61. The impedance of a test coil usually can be represented by the vector sum of:a. inductive reactance and resistanceb. capacitive reactance and resistancec. inductive reactance and capacitive reactanced. inductance and capacitanceA. 51


62. For age hardenable aluminum and titanium alloys, changes in hardness are indicated by changes in:a. retentivityb. permeabilityc. conductivityd. magnetostrictionE.59


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


63. The penetration of eddy currents in a conductive material is decreasedwhen:a. test frequency or conductivity of the specimen is decreasedb. test frequency is decreased or conductivity of the specimen isincreasedc. test frequency, conductivity of the specimen or permeability of thespecimen is increasedd. permeability of the specimen is decreasedA. 54

δ= 1/√(πfμσ) = (πfμσ) -½


64. When the alternating current in an eddy current coil reverses direction:a. the direction of the eddy currents in a part remains the sameb. the eddy currents in the test part will change phase by 45°c. the direction of the eddy currents in the part also reversesd. the eddy currents in the part remain the sameE.14

65. To be useful, limit frequency equations fg must be:a. used with their impedance diagramsb. used to determine their impedance diagramsc. both a and bd. neither a nor bE.85


66. When a rod is placed in an encircling type of coil, the density of eddy currents will be the greatest:a. at the surfaceb. at the centerc. midway between the surface and the centerd. none of the aboveA.130,151

67. The term fill factor applies to:a. a surface coilb. coaxial cablec. an encircling coild. all of the aboveA.130


68. An eddy current system using handling equipment with automatic marking of the defective areas primarily makes it possible to:a. remove defective areas of the product, if desiredb. eliminate test surface contaminationc. allow an inexperienced operator to establish the discontinuity caused. pass rejectable materialE.98


69. Two test coils are often used in a bridge circuit to:a. eliminate skin effectb. determine the differences between a known standard sample and a test piecec. increase the conductivity of the circuitd. decrease the system sensitivityA.178

70. The actual frequencies used in any specific eddy current inspection should be selected on the basis of the:a. thickness of the materialb. desired depth of penetrationc. degree of sensitivity or resolution requiredd. all of the aboveE.83


71. The term used to define the difference between actual instrument outputand expected output as defined by a straight line calibration curve is:a. phase shiftb. nonlinearityc. lift -offd. skin effectA.324-325

72. A term used to define any change in a sinusoidal signal when the outputis not a linear reproduction of the input is:a. distortionb. linearityc. phase shiftingd. dynamic rangeH.40.41


73. The magnetic domains in an unmagnetized ferromagnetic material:a. are arranged to facilitate the conduction of electronsb. are randomly oriented and neutralize each otherc. are uniformly orientedd. create a major north and south pole in the materialE.44

74. When a magnetic material is placed in a region of an applied magnetizing force, a magnetic field is developed in the material by means of:a. inductionb. conductionc. heat transferd. magnetic domain transferH.30.6


75. The atoms of a metal showing magnetic characteristics are grouped intoregions that are the smallest known permanent magnets. These regions are called:a. lattice structuresb. cellsc. domainsd. planetary spinsE.44

76. The flux density in a magnetized material is usually designated by the:a. symbol μ (permeability μ=B/H)b. symbol σ (conductivity σ= 1/ρ)c. letter Bd. letter H (magnetic field intensity)H.30.22


77. The magnetizing force of a saturation coil is usually designated by the:a. symbol μ (permeability μ=B/H)(H·m-1 or N·A-2)b. symbol σ (conductivity σ= 1/ρ)(Siemens/meter)c. letter B (Tesla, Gauss)d. letter H (magnetic field intensity) (Ampere-meter?)H.30.22

78. The ratio of a material's flux density to the applied magnetizing force can be used to determine the material's:a. Permeability μ=B/Hb. conductivityc. resistivityd. lift-off8.2.14


79. The two sine wave signals (V and I) shown in Figure 6 are:a. in phaseb. 45 degrees out of phasec. 90 degrees out of phased. 180 degrees out of phase8.2.36


80. The two sine wave signals (V and I) shown in Figure 7 are:a. in phaseb. 45 degrees out of phasec. 90 degrees out of phase current lags voltage by 90º -d. 180 degrees out of phase possibly inductive circuit

8.2.37


81. The symbol commonly used to signify impedance is:a. Zb. XLc. Rd. XC

82. In Figure 8, H represents:a. the magnetizing forceb. the material's flux densityc. the material's permeabilityd. the material's conductivityB.2.18


83. In Figure 8, B represents:a. the magnetizing forceb. the material's flux densityc. the material's permeabilityd. the material's conductivityB.2.18

84. In Figure 8, the distance represented by A is a measure of the material's:a. permeabilityb. conductivityc. retentivityd. coercive forceB.2.18


85. In Figure 8, the distance represented by C is a measure of the material's:a. permeabilityb. conductivityc. residual magnetismd. coercive forceB.2.18


86. A term used to define a property of a test system which enables theseparation of signals due to discontinuities in the test specimen that arelocated in close proximity to each other is:a. dynamic rangeb. sensitivityc. linearityd. resolutionH.43.49

87. The inductive reactance of a coil is measured in units of:a. mhosb. ohmsc. henriesd. gauss8.1.22


88. A term used to defme a surface or internal rupture that is attributed toprocessing at too low a temperature or excessive working or metal movementduring the forging, rolling or extruding operation is:a. a cold shutb. microshrinkagec. burstd. an inclusionB.A-10


Eddy Current Testing Level III Q&A

Three


Answers to Eddy Current Testing Level III1.d 2.d 3.b 4.c 5.d 6.a 7.a 8.b 9.b 10.c 11.d 12.a 13.d 14.b15.a 16.b 17.c 18.d 19.b 20.a 21.a 22.d 23.c 24.d 25.d 26.a 27.e 28.a 29.c 30.e 31.b 32.b 33.d 34.e 35.d 36.a 37.a 38.b 39.b 40.d 41.a 42.a 43.c 44.d 45.c 46.b 47.c


1. In a feed through encircling coil eddy current system, a calibration standardmay be used to:a. ensure repeatability and reliability of the setupb. calibrate the approximate depth of detectable discontinuitiesc. measure the test frequencyd. both a and bA.271

2. A calibration standard may be used with a rotating probe eddy current instrument to:a. produce an indication relative to the depth of the discontinuityb. check the instrument for repeatability and freedom from driftc. check probe coil for possible damaged. all of the aboveA.271


3. Handheld probe-type eddy current tests are most useful in:a. detection of surface and subsurface inclusionsb. detection of surface discontinuities such as overlaps and seamsc. detection of internal piping or burstsd. all of the aboveA.358


4. In eddy current testing of tubing with low permeability values, a DC saturation approach might be provided by:a. an encircling solenoidb. permanent magnetsc. either a or b depending upon the test environmentd. neither a nor bD.19


5. In Figure 9, AC current flowing through a primary coil sets up a magneticfield and causes a flow of eddy currents in the rod. The voltage induced in thesecondary coil is dependent upon:a. these eddy currentsb. the primary coilc. the generatord. all of the aboveD.11


6. Which of the following is not a method that might be used to improve thesignal-to-noise ratio?a. increase the amplification of the test instrumentb. change to a test frequency that will decrease the noisec. improve the fill factord. enable filter modes in the instrumentA.173/0.25


7. Which of the following is a property of eddy currents induced in a conductorby an encircling coil?a. the eddy current flow is affected by permeability variations in the sampleb. the magnitude of eddy current flow is large compared to the current flow inthe coilc. the eddy current flow dissipates no power in the conductord. none of the aboveD.3

8. Which of the following is a property of eddy currents induced in ahomogeneous conductor by an encircling coil?a. they are weakest on the conductor surfaceb. the phase of the eddy currents varies throughout the conductorc. they travel in straight linesd. they are maximum along the coil axisD.4

Jx =Joe–x/δ , δ = (πfμσ) -½ , ϴ = x/δ rad.


9. Which factor does not affect the phase shift between the transmitted signaland the reflected signal for a reflection coil (assuming the part isnonferrornagnetic)?a. the conductivity of the sampleb. the magnitude of the transmitted signal θ = x/δ = x∙√(πfμσ)c. the thickness of the sampled. the presence of discontinuities in the sample (?)D.11,56


10. The tubular product parameter having the greatest influence on theprimary flux distribution throughout a nonferromagnetic part is the:a. surface roughness of the productb. outside diameter of the productc. wall thickness of the productd. length of the productA.148

11. Any handling equipment used in an eddy current system must take intoconsideration:a. the operator's abilitiesb. the end use of the product being testedc. speed, frequency of the test, sorting speed and physical control of theproductd. all of the aboveA.356


12. An eddy current system can be calibrated to provide qualitative rating and material marking where the product being inspected:a. does not allow defective areas to be removedb. is not defectivec. is of inferior qualityd. has inconsistent qualityA.356

13. When conducting an eddy current inspection using an automatic handlingsystem, it is advisable to calibrate and adjust the sensitivity levels to:a. some electronic sourceb. another NDT methodc. an NIST standardd. an actual test part being inspectedA.274


14. A distinct advantage of using handling equipment in an eddy current testsystem is to reduce the potential for errors caused by:a. instrument driftb. lift-offc. skin effectd. all of the abovee. none of the aboveA.364


15. Decreased coupling or fill factor will resultin decreased test sensitivity because:a. reduced coupling between the specimen and the pickup coil results insmaller voltages across the pickup coilb. reduced coupling between the driver coil and the specimen increases eddycurrent flow in the specimenc. reduced coupling between the driver coil and the specimen will increase the signal-to-noise ratiod. all of the above0.24

16. Why is it desirable to hold the fill factor or lift-off constant?a. to avoid arcing between the coil and the specimenb. to minimize test output signal changes that are not relevant to conditions within the specimen to be testedc. because a fill factor or lift-off change will shift the operating frequencyd. to minimize the load on the constant current AC excitation circuitsA.356


17. The reactance component is decreased by placing a conducting object inthe coil's electromagnetic field. Why is this so?a. the secondary field is exactly in phase with the primary fieldb. the secondary field is at precisely 90° with the primary fieldc. the phase angle between the two field components is always greater than90° which partially cancels the primary fieldd. the secondary field is 180° out of phase with the primary field which causes a large phase shiftD.4

Comment: the reasoning for choosing “d” is the Lenz’s law.(more reading on the correct choice of “c”)


21. An alternating current produces eddy currents in a test object. The vector Hs represents the secondary AC field in the test piece. What function occurs to produce a workable test situation? (See Figure 10.)a. changes in the test specimen, such as cracks, metallurgical or dimensional changes, will alter the secondary field phase and amplitudeb. the primary alternating current must be 60 cycles to produce this effectc. a temperature rise in the specimend. a mismatch of the Hp and Hs fields produces a change in the outputD.5

Figure 10


18. Test coils may be shielded with either high conductivity or high permeability materials to:a. shape the fieldb. increase sensitivityc. increase resolutiond. all of the abovee. none of the aboveA.144/0.22

19. When a ferromagnetic bar is placed in the coil's electromagnetic field, the coil's reactance is increased. What causes this phenomenon?a. the coil becomes magnetically saturatedb. the ferromagnetic test sample's permeability raises the inductance ofthe test coilc. the ferromagnetic test sample's conductivity increases the reactancevalue of the coild. none of the above; a ferromagnetic bar would cause the coil's reactance todecrease0.22


20. Eddy currents flowing in the test object at any depth produce magnetic fields at greater depths, which oppose the primary field, thus reducing its effect and causing what kind of change in current flow as the depth increases?a. a decreaseb. an increasec. a frequency changed. none of the above0.5


21. An alternating current produces eddy currents in a test object. The vectorHs represents the secondary AC field in the test piece. What function occursto produce a workable test situation? (See Figure 10.)a. changes in the test specimen, such as cracks, metallurgical or dimensional changes, will alter the secondary field phase and amplitudeb. the primary alternating current must be 60 cycles to produce this effectc. a temperature rise in the specimend. a mismatch of the Hp and Hs fields produces a change in the outputD.5

Figure 10


22. Skin effect causes eddy currents to tend to flow near the surface of thetest piece. Which of the following factors alter the skin effect?a. testing frequency:b. test piece temperaturec. test piece hardnessd. all of the aboveD.23

23. When an excitation voltage is applied to a coil, the primary magnetic flux is in phase with the current. No secondary magnetic flux is present When atest object is inserted in this coil, what action takes place?a. the object gets hot and no information is availableb. insertion of the object cancels all informationc. a secondary magnetic flux is produced, thus creating a new total magnetic flux which can be used to supply test informationd. by subtractiug the relative values of the primary flux and voltage vectorsfrom the secondary components, it is possible to predict the net oscillatorpower consumption0.5


24. The electromagnetic field in a test specimen during eddy current testing isdescribed by:a. Bessel functionsb. exponential functionsc. algebraic functionsd. all of theseA.33/D.2/E.85/H.36.13

25. There is one function that responds to variations in eddy currentdiscontinuity and magnetic field conditions. This function actually producesthe output signal from the coil. What is this function?a. phasingb. resistancec. reactanced. impedanceD.21


26. To separate cracks and diameter effects for steel cylinders, the optimumfrequencies correspond to f/fg ratios of less than (see Figure 11):a. 10b. 15c. 50d. 1000.28,30


27. The inductive reactance of a test coil, which is one of the most importantimpedance quantities, depends upon which of the following?a. frequency, coil inductance and coil resistanceb. coil inductance onlyc. coil resistance and inductance only XL=2πfLd. frequency and coil resistance onlye. frequency and coil inductance onlyD.16


28. Figure 12 indicates that the largest eddy current indications from subsurface cracks will occur when the frequency ratio (f/fg) is:a. 5 or lessb. 15c. 50d. 150 or moreD.28,30


29. An operating frequency of 100kHz will have the deepest penetration in:a. titaniumb. copperc. stainless steeld. aluminumD.22,27

30. Disadvantages of using a surface probe coil for the inspection of small-diameter tubing include:a. inability to detect small discontinuitiesb. slow inspection speedc. inherent Mechanical problemsd. both a and ce. both b and cD.9/E.29


31. Figure 13 indicates that the magnitude of a signal from a subsurface crack will increase when the frequency ratio (f/fg):a. remains the sameb. decreasesc. increasesd. none of the aboveD.28,30

Comment:Maximum at f/fg = 15decreasing on both sides


32. Figure 13 indicates that when inspecting for surface cracks in nonferromagnetic cylinders, the optimum frequency ratio (f/fg) is between:a. 5 and 10b. 10 and 50c. 50and100d. 100 and 150D.28,30

33. Of the following eddy current systems, which would be considered best for detection of small discontinuities in tubing?a. surface probe coilsb. encircling coilsc. inside probe (ID) bobbin coilsd. both b and c0.9/E.29


34. In a send-receive system, when the sensing coil is placed near the excitation coil, which of the following statements is true?a. almost the same magnetic flux threads both coilsb. signals from either coil can be used to provide information about the testPiece (?)c. the arrangement is never sensitive to small discontinuitiesd. all of the abovee. both a and bD.11

35. A primary-secondary coil inspection system is being used. To suppressthe primary coil signal induced in the secondary coil, one might:a. use a differential-type secondary coilb. add a 180º out-of-phase input signal to the induced signalc. subtract an in-phase (input) signal from the induced signald. any of the aboveE.33


36. Which material should be selected to provide the most effective shieldingof a test coil from an external RF field?a. Fiberglassb austenitic stainless steelc. copperd. brassD.18

37. Which type of readout mechanism would be best for the detection of anonrepetitive discontinuity indication during high speed testing?a. a storage-type LCD screen (?)b. a meterc. a system using short –persistence window logicd. a dual beam typeD.40


38. Impedance changes produced by small lift -off variations are greatestwhen:a. there is a nonconductive coating on the test materialb. the probe is usually in contact with the test materialc. lower test frequencies are usedd. large diameter coils are usedD.23

39. As the operating frequency is increased, the impedance of the empty coil:a. decreasesb. increasesc. remains the same XL= 2πfL, Z= √(R2+XL

2)d. none of the aboveD.17/J.81


40. When testing for the unknown conductivity of a metal, the measureconductivity (σ) is strongly affected by:a. I2Rb. material thickness variations beyond the three delta point in tbe testspecimenc. coil diameterd. specimen temperatureD.21

41. In selecting a coil for multifrequency tests:a. bandwidth is of major importanceb. frequency response is of minor importancec. the Q of the coil should be less than 1d. the Q of the coil should be less than the inductanceD.37


42. In developing a multifrequency test, the parameter separation limitationsare greatest for those parameters producing:a. nearly similar signalsb. 0° to 90° phase shiftsc. signals having no electrical relationd. 90° to 110° phase shiftsD.37

43. Mutual inductance describes:a. the effect two coils have on each otherb. the coupling between the test coil and test partc. a and bd. neither a nor bE.17

Comment: No restricted to coil-coil interaction only!This include test piece-coil mutual inductance.


44. Increasing the heat-treating temperature of nonferrous metals:a. increases electrical conductivityb. will have no effect on electrical conductivityc. will decrease electrical conductivityd. may either increase or decrease electrical conductivity, dependingupon the alloy and the nature of the heat treatmentD.22/H.42.19

45. Limit frequency fg is defined when the argument of the mathematicalfunction describing the electromagnetic field within a test specimen is setequal to:a. 0b. 0.37c. 1d. 6.25D.28


46. Figure 14 illustrates that the separation of diameter effects and conductivity effects:a. can be accomplished at any f/fg ratiob. can best be accomplished at f/fg ratios larger than 4c. can best be accomplished at f/fg ratios less than 4d. cannot he accomplished at any f/fg ratioD.28

Charlie C

hong/ Fion Zhang


47. Figure 15 illustrates:a. variations in fill factor for a solid rodb. variations in fill factor for a thin-walled tubec. transition between a solid rod andthin-walled tubed. all of the aboveD.24,29


making


Good Luck

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

Electromagnetic testing q&a 004

Engineering

Transcript of Electromagnetic testing q&a 004