electromagnetic testing q&a 001

Electromagnetic TestingQuestions & Answers -001EC&FL Testing-Book(E) 1995My ASNT Level III Pre-Exam Preparatory My Self Study Notes 10th April 2015

Charlie Chong/ Fion Zhang


Petrochemical Applications



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1. A test specimen used as a basis for calibrating test equipment or as a comparison when evaluating test results is referred to as a:A. Null‐BalancerB. Phase ShifterC. Reference StandardD. High Pass Filter

2. In an eddy current testing situation, which of the following can provide sources of noise?A. Instrumentation Electronic CircuitsB. Nonspecific Variations With The Test ObjectC. Electrical interferenceD. All Of The Above

Tallied choice & standard answer

Standard answer

My Choice of wrong answer


Eddy Current Testing Method


Level I Q&A


Level I - Standard Answers

1. C 2. D 3. B 4. D 5. C 6. A 7. B 8. A 9. A 10. A 11. D 12. B 13. D 14. C 15. D 16. B 17. A 18. C 19. C 20. B 21. B 22. D 23. A 24. C 25. B

26. D 27. B 28. C 29. D 30. A 31. D 32. B 33. D 34. C 35. D 36. B 37. A 38. D 39. A 40. B 41. B 42. C 43. D 44. B 45. D 46. A 47. B 48. C 49. D 50. B

51. B 52. C 53. B 54. D 55. B 56. C 57. D 58. B 59. B 60. A 61. C 62. C 63. B 64. C 65. B 66. D 67. B 68. A 69. D 70. B 71. A 72. D 73. C 74. B 75. A

76. D 77. C 78. D 79. B 80. A 81. B 82. C 83. B 84. A 85. A 86. A 87. B 88. C 89. C 90. B 91. D 92. B 93. D 94. B 95. A 96. A 97. C 98. D 99. C


1. A test specimen used as a basis for calibrating test equipment or as a comparison when evaluating test results is referred to as a:A. Null‐BalancerB. Phase ShifterC. Reference StandardD. High Pass Filter

2. In an eddy current testing situation, which of the following can provide sources of noise?A. Instrumentation Electronic CircuitsB. Nonspecific Variations With The Test ObjectC. Electrical interferenceD. All Of The Above

3. The ratio of the response or amplitude from signals of interest to the response or amplitude of the 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 Ratio XL/R ?


4. IACS is recognized abbreviation for:A. Induced Alternating Current SystemB. Inductively Activated Comparison SystemC. Internal Applied Current SystemD. International Annealed Copper Standard

5. Which of the following is not basic component of eddy current equipment?A. AmplifierB. CoilC. Liquid CouplantD. Detector

6. The process of comparing the reading or output of an instrument, device, or dial with a standard to determine the instrument’s accuracy, capacity, or graduations is referred to as:A. CalibrationB. DifferentiationC. IntegrationD. Phase Shifting


7. When conducting an eddy current test using a differential comparison coil arrangement that compares an external reference standard with the test specimen, 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 Coil

8. The impedance of an eddy current test coil will increase if the:A. Test Frequency Increases XL=2πfLB. Inductive Reactance Of The Coil DecreasesC. Inductance Of The Coil DecreasesD. Resistance Of The Coil Decreases

9. 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 Above


FIGURE 8-44 Impedance plane before normalization. (a) Movement of air point with change in frequency. (b) Variation of conductance with frequency

XL= 2πfL

X L X L


FIGURE 8-45 Effect of test variables on impedance curve operating point.

Factors that increase current flow (of induced eddy current?)result in clockwise movementof the impedance operating point along the semicircle,

while those that restrict current flow result in counterclockwise movement of the operating point， as seen in Figure 8-45.


10. Which of the following would normally be considered the best fill factor when testing straight tubing with an encircling or feed through coil?A. 0.95 (95%)B. 1.75 (175%)C. 0.50 (50%)D. 0.25 (25%)

11. When a magnetic metal part is placed in an eddy current test coil, the impedance of the coil will be change by which of the following properties of the part?A. ConductivityB. DimensionsC. PermeabilityD. All Of The Above Electric (conductivity) /Magnetic (permeability, dimensions) Factors

12. An eddy current is circulating electrical current induced in a conducting article by:A. Gamma RaysB. An Alternating Magnetic FieldC. A piezoelectric ForceD. Any Of The Above


13. The conductivity of a material can be changed by changing the:A. Alloy Of The SpecimenB. Heat Treatment Of The SpecimenC. Temperature Of The SpecimenD. All Of The Above

14. Figure 1 is an illustration of the material’s:A. Phase Analysis LoopB. Sine WaveC. Hysteresis LoopD. None Of The Above

15. When testing ferromagnetic materials, 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 MaterialD. All Of The Above δ = (2/ωμσ)-½


Figure 1


16. 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 Effect

17. 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 Effect

18. Lift off is utilized in:A. Measuring Permeability changesB. Measuring Conductivity ChangesC. Measuring The Thickness Of Nonconductive CoatingsD. Determining Proper Test Frequency


19. In eddy current test systems where encircling coils are used, coupling efficiency is referred to as:A. Lift OffB. Edge EffectC. Fill FactorD. Phase Differentiation

20. When inspecting products with a uniform cross section, an eddy current signal is produced when the leading end or trailing end of the product approaches the test coil.This phenomenon is referred to as:A. Lift OffB. End Effect (edge effect?)C. Fill FactorD. Phase discrimination

21. Which of the following conditions would be the most difficult to detect when eddy current testing 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 conductivity


22. When testing tubing with an inside diameter 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 Tubing

23. Which of the following test frequencies would produce eddy currents with the largest depth of penetration?A. 100 HzB. 10 kHzC. 1 MHzD. 10 MHz

24. An eddy current test coil’s opposition to the flow of alternating current is called:A. ResistanceB. Inductive Reactance (XL)C. Impedance (Z) [Z = R + jωL = R+ j2πfL = R+ jXL = √(R2+XL

2)]D. Capacitive Reactance

→


Eddy Current Bobbing Coil

http://www.ndt.net/search/docs.php3?id=14618&content=1


Eddy Current Impedance Diagram

https://www.nde-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/impedance.htm


25. An increased in the impedance of an eddy current test coil will:A. Cause An Increase In The Current Flow Through The Test CoilB. Cause A Decrease In The Current Flow Through The Test CoilC. Not Affect Current Flow In The Test CoilD. Decrease The Voltage Applied To The Coil


Recalling the mistakes


26. Which of the following will affect the impedance of an encircling eddy current test probe?A. Conductivity Of A Test Specimen In The CoilB. Permeability Of A Test Specimen In The CoilC. Fill FactorD. All Of The Above

27. When a test coil consists of a double winding arrangement, and one winding is referred to as a primary winding, the other winding is referred to as the:A. Absolute WindingB. Secondary WindingC. Phase WindingD. None Of The Above

28. Eddy current test coils which are wound to form a wide coil would normally be used to detect:A. PittingB. Small InclusionsC. Change In Conductivity D. Porosity


29. Eddy current test coils, which are wound to form a narrow coil, would normally be used to detect:A. Slow Changes In DimensionsB. Gradual Changes In ConductivityC. Variation In Heat TreatmentD. Small Surface Defects

30. Direct current saturation coils would most likely be used when testing:A. SteelB. AluminumC. CopperD. Brass

31. The single absolute coil arrangement can be used in:A. Encircling Coil OnlyB. Probe Coils OnlyC. Probe And Encircling Coils OnlyD. Probe, Encircling, And Inside Diameter Coils


32. The primary purposes of the secondary winding in an eddy current coil is to:A. Induce Eddy Currents In The Test SpecimenB. Detect Changes In The Eddy Current FlowC. Induce Eddy Currents In The Test Specimen And To Detect Changes In The

Eddy Current FlowD. Provide Desaturation

33. Which of the following eddy current test coil arrangements uses one of the test specimens as a reference standard against which another area on the same specimen is simultaneous compared?A. Single Absolute CoilB. Double Absolute CoilC. Desaturation CoilD. Differential Coil

34. The readout mechanism used when testing by the ellipse method is a:A. MeterB. Strip Chart RecorderC. Cathode Ray TubeD. Any Of The Above


35. Reference standards used for eddy current 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 Of

Discontinuities Depending On The Test System And The Type Of Test Being Conducted

36. A reference standard used to ensure that the amplitude and phase characteristics of an eddy current system do not drift during continuous testing is called a:

A. DGS StandardB. Calibration StandardC. Reference BlockD. None Of The Above

37. Which of the following could not be tested by the eddy current testing method?A. A 102 mm (4 in.) Thick Plate To be Tested For Small Discontinuities

Throughout 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 Diameter


I


38. Which of the following is not applicable to eddy current testing?A. Can Be Used For High Speed TestingB. Can Accurately Measure ConductivityC. Can Be Set Up To Provide High Sensitivity To Small DiscontinuitiesD. Can Penetrate Up To 152 mm (6 in.) In A Test Part

39. The entire circumference of a test part is evaluated at one time when using:A. An Encircling CoilB. A Probe CoilC. A Secondary WindingD. None Of The Above

40. When attempting to determine the exact point location of a discontinuity, the test system should include:A. A Phase ShifterB. A Probe CoilC. An AttenuatorD. A Pentameter


41. It is often possible to sort various nonmagnetic alloys of a metal by means 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 Current Varies For Each AllowD. The Magnetic Domains For Each Alloy Are Different

42. Which of the following products would be most applicable to a test using an inside coil?A. SheetB. RodC. Bolt HoleD. Coating Thickness

43. 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. Rod Is Fed Through The Coil At Varying SpeedsC. All Of The AboveD. None Of The Above


74. Material must be reasonably centered in the test coil of flaw detection system because:

A. The Coil Would Otherwise Be Out Of BalanceB. Parts of the material furthest away from the coil radially, may receive a

less sensitive inspectionC. The Flow Of Eddy Current Around The Product Will Be Disturbed,

Resulting In Improper PenetrationD. Lack Of Proper Centering May Change The Phase Adjustment Of the

Instrument


44. One method of reducing nonrelevant indications when eddy current testing ferromagnetic material 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 The Coil

45. Eddy currents are circulating currents induced in a conducting material by a:A. Varying Piezoelectric FieldB. Standing Wave FrontC. Direct CurrentD. Varying Magnetic Field

46. In order to generate measurable eddy currents in a test specimen, the specimen must be:A. A ConductorB. An InsulatorC. Either A Conductor Or InsulatorD. A Ferromagnetic Material


47. All ferromagnetic materials that have been magnetically saturated to suppress permeability variations may retain a certain amount of the magnetization called the:A. Coercive ForceB. Residual MagnetismC. Hysteresis LoopD. Hysteresis Loss

48. An AC 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 Above

49. 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 CurrentD. All Of The Above


50. 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 Coils


51. Which of the following is not a read out system used to present eddy current test information?

A. Calibrated And Uncalibrated MetersB. Litmus PaperC. Cathode Ray TubeD. Strip Chart Recorders

52. Which of the following statements best describes the selection of eddy current test frequency?

A. The Frequency Must Equal The f/fg Ratio To Give An Accurate TestB. The Frequency Must Be Within + or ‐ 3% Of The f/fg Ratio To Give An Accurate

TestC. There Is A Range Of Suitable Frequencies Centered Around The Optimum

FrequencyD. The Frequency Should Be Within + or ‐ 25% Of The Characteristic Frequency

53. Which Of the Following Is Not A Method That May Be Used To Improve The Signal To Noise Ratio?

A. Change To A Test Frequency That Will Decrease The NoiseB. Increase The Amplification Of The Test InstrumentC. Improve The Fill FactorD. Add Filter Circuits To The Instrument


54. When conducting an eddy current test on tubing, the magnitude of the indication caused by a discontinuity is dependent on:A. The Depth Of The DiscontinuityB. The Width Of The DiscontinuityC. The Length Of The DiscontinuityD. All Of The Above

55. A coil’s magnetic field may be viewed as a distribution of lines of flux around the coil. The number of lines in a unit area is defined as:A. Magnetic DensityB. Flux DensityC. Magnetic CouplingD. Hysteresis Density

56. Which of the following discontinuities would be easiest to detect with an eddy current test?A. A Crack That Lies parallel To The Direction Of The Eddy Current FlowB. A Discontinuity Located In The Center Of A 51 mm (2 in.) Thick Diameter RodC. A Radial Crack That Extends To the Outer Surface Of A RodD. A Subsurface Radial Crack Located At A Depth Of 13 mm (0.5 in.) In A 51 mm

(2 in.) Diameter Rod


57. Eddy current test techniques can be used to:A. Measure Coating ThicknessB. Measure Cladding ThicknessC. Gauge The Thickness Of SheetD. All Of The Above

58. Eddy currents cannot be induced in:A. AluminumB. Latex PaintC. SteelD. Copper

59. Which of the following characteristics do not apply to magnetic materials?A. High Permeability ValueB. No Hysteresis loopC. Definite Saturation Point On Hysteresis LoopD. Appreciable Residual Magnetism


60. Which of the following is not an eddy current testing method?A. Pulse Echo TestingB. Impedance TestingC. Phase Analysis TestingD. Modulation Analysis Testing

61. Eddy current always travel:A. In Nonconductive MaterialsB. Radially When Testing Rod With An Encircling CoilC. In Closed PathsD. In A Gas

62. For the purposes of eddy current testing, saturation of ferromagnetic material is reached when the current is at such a value that for any further increase in current the signal to noise ratio will:A. Start To IncreaseB. Start To DecreaseC. Show No Significant ChangeD. Suddenly Drop To Zero


63. When sorting a known mix of two alloys with a comparator having a quantitative readout device, it is desirable to hold 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 Correctly

64. A term used to define a condition of balance in a device or system which results in zero output is:A. High Frequency StandardizationB. IntegrationC. Null BalanceD. Differentiation

65. A term used to define a condition of balance in a device or system which results in zero output is:A. A MaxwellB. A GaussC. An OhmD. A Mho


66. Changes in the hardness of age hardenable aluminum and titanium alloy will normally be accompanied by change in:A. RetentivityB. PermeabilityC. MagnetostrictionD. Conductivity Hardness ≡ conductivity

67. A term used to describe holes, grooves, notches, etc., that are introduced into a reference standard to provide accurately reproducible quality level is:A. A Natural DiscontinuityB. An Artificial DiscontinuityC. An EllipseD. None Of The Above

68. 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 Oscillator


69. 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 Production TechniquesD. All Of The Above

70. The region around a magnet that attracts other pieces of iron or steel is called:A. A MaxwellB. The Magnetic FieldC. RetentivityD. Alternating Current

71. 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 Above


72. Which of the following are common applications for eddy current testing?A. Measurement Of Conductivity Or Combination Of Conductivity And PermeabilityB. Measurement Of The Thickness Of Thin Metal Sections, Cladding, Or CoatingC. Detection Of Surface And Subsurface DiscontinuitiesD. All Of The Above

73. Which of the following is not primary purpose for using an eddy current standard?A. Determine If The Eddy Current Test System Is Capable Of Performing The Test

ProperlyB. Determine If A discontinuity Is Cause For RejectionC. Determine The instrument Control Settings Needed To pass The Highest

Percentage Of Test Specimens RunD. Determine If The Sensitivity Of A Test System Has Drifted With Time


74. Material must be reasonably centered in the test coil of flaw detection system because:

A. The Coil Would Otherwise Be Out Of BalanceB. Parts of the material furthest away from the coil radially, may receive a

less sensitive inspectionC. The Flow Of Eddy Current Around The Product Will Be Disturbed,

Resulting In Improper PenetrationD. Lack Of Proper Centering May Change The Phase Adjustment Of the

Instrument


75. When you determine that a flaw detection instrument has been set up incorrectly, or is defective, all material:A. Should Be Retested Since The Time Correct Set Up Or Proper

Operation Was Last VerifiedB. Accepted Should Be RetestedC. Rejected Should Be RetestedD. None Of The Above


76. An eddy current system (60 cycle comparator type) 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 Above

77. A length of tubing containing a notch running from end to end and having uniform width and depth, when tested with an encircling self reference differential coil system, will produce:A. Erratic SignalsB. A Continuous, Sustained SignalC. No SignalD. Excessive Signals

78. In eddy current testing, optimum sensitivity to a known defect placed at random on the surface of a nonferrous length of tubing is obtained by:A. Proper Choice Of FrequencyB. Centering The Tubing In The CoilC. Proper Adjustment Of PhaseD. All Of The Above


79. Spinning probe type eddy current instruments are most useful in the detection of:A. Surface And Subsurface InclusionsB. The Smallest Surface BlemishesC. Internal Piping Or BurtD. All Of The Above

80. One principal advantage of spinning probe eddy current instruments is:A. The Ability To Locate The Circumferential Position Of DefectsB. Relative Insensitivity To VibrationC. The Variety Of Internal And Surface Defects That May Be detectedD. All Of The Above

81. At any given instant, a spinning probe eddy current instrument should be inspecting: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. One Of The Above


82. A spinning probe eddy current instrument would be most useful in:A. Measuring Hardness Of Ferromagnetic Steel ProductsB. Flaw Detection In Hexagonal And Shaped MaterialC. Detecting And Precisely Locating Surface And Subsurface

DiscontinuitiesD. Inspection Of Copper Bus Bars For Electrical Conductivity

83. Which of the following is not a nondestructive testing method?A. Ultrasonic TestingB. Fatigue TestingC. Eddy Current TestingD. Radiographic Testing

84. Which of the following is not applicable to spinning probe type instruments?A. The Size Of Product To Be Inspected Is Limited By The DC Saturation

Capability of The SystemB. The Frequency May Be Varied To Accommodate Various Metals And

AlloysC. They May Be Used On Straight Or Coiled Wire ProductsD. They Are Useful In Seam Detection


85. In a feed through encircling coil eddy current system, a calibration standard may be used to:A. Insure Repeatability And Reliability Of The SetupB. Precisely Calibrate The Flaw DepthC. Reduce Sensitivity To VibrationD. Measure The Test Frequency

86. What causes phase shift in an eddy current test coil?A. A Change In The Ratio Of Inductive Reactance (XL) To Resistance RB. A Change In The Sensitivity Setting Of The InstrumentC. Use Of Modulation AnalysisD. None Of The Above

87. In a feed through encircling coil flaw detection eddy current system, what would be the purpose of running a calibration defect several 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 Speed


88. In a feed through encircling coil eddy current system, DC saturation would probably be most helpful in testing:A. Copper Water TubingB. Titanium TubingC. Ferromagnetic Steel TubingD. Brass Rivet Wire

89. In a feed through encircling coil eddy current system, the test frequency is controlled by the:A. OscilloscopeB. Sensitivity SettingC. OscillatorD. Modulation Analysis Setting

90. Alloy variations in nonmagnetic material would most likely affect:A. PermeabilityB. ConductivityC. DiameterD. Frequency


91. Which of the following frequencies will provide the greatest eddy current penetration in aluminum?A. 1 kHzB. 10 kHzC. 3 kHzD. 300 Hz

92. The coercive force of a soft iron electromagnetic core would be the ______________ coercive force of a permanent magnet.A. Greater ThanB. Less ThanC. TwiceD. Equal To

93. Metals that do not react or react only slightly to magnetic fields are called:A. Diamagnetic MetalsB. Paramagnetic MetalsC. Nonmagnetic MetalsD. All Of The Above


94. A symbol commonly used to express conductivity is:A. μB. σC. XLD. R

95. A symbol commonly used to express permeability is:A. μB. σC. XLD. R

96. The method used to generate eddy currents in a test specimen by means of a coil can most closely be compared with the action of a:A. TransformerB. CapacitorC. Storage BatteryD. Generator


97. 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 Above

98. Demagnetization is generally needed when the residual field in a specimen:A. May Affect The Operation Or Accuracy of Instruments When The Specimen Is Placed 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 Necessary

99. A term used to define testing that requires that the test article be loaded and or sectioned to verify and or establish mechanical or physical properties is:A. Impedance TestingB. Phase Analysis TestingC. Destructive TestingD. Nondestructive Testing


Lesson Learned


Eddy Current Testing Level I (20 Questions)1.B2.B3.C4.B5.D6.B7.C8.D9.B10.D11.D12.C13.B14.B15.D16.B17.D18.D19.C20.A

http://ndt-samplequestions.blogspot.com/2011/06/eddy-current-testing-level-i-20.html


Q.1 Generation of eddy currents depends on the principle of:A. wave guide theory.B. electromagnetic induction.C. magneto-restrictive forces.D. all of the above.

Q.2 A secondary field is generated by the test object and is:A. equal and opposite to the primary field.B. opposite to the primary field, but much smaller.C. in the same plane as the coil is wound.D. in phase with the primary field.

Q.3 When a non-ferromagnetic part is placed in the test coil, the coil's voltage:A. increases.B. remains constant because this is essential.C. decreases.D. shifts 90 degrees in phase.



Q.4 Eddy currents generated in a test object flow:A. in the same plane as magnetic flux.B. in the same plane as the coil is wound.C. 90 degrees to the coil winding plane.D. Eddy currents have no predictable direction.

Q.5 The discovery of electromagnetic induction is credited to:A. Arago.B. Oersted.C. Maxwell.D. Faraday.

Q.6 A standard depth of penetration is defined as the point in a test object where the relative eddy current density is reduced to:A. 25 percent.B. 37 percent.C. 50 percent.D. 100 percent.



Q.7 Calculate the standard depth of penetration at 10 kHz in copper; σ = 5.7•107 mhos per meter. A. 0.1 mmB. 0.02 mmC. 0.66 mm δ = √ (2/ωμσ) = √(2/πfσμ) = (πfσμ)-½ , D. 66 mm (for non-magnetic material μ = 4π x 10-7 N∙A-2) (remember this!)

Q.8 Differential coils are usually used in:A. bobbin coils.B. probe coils.C. OD coils.D. any of the above.

Q.9 When using a probe coil to scan a test object,______A. the object must be dry and polished.B. the object must be scanned carefully to insure inspection coverage.C. the object must be scanned in circular motions at constant speeds.D. the probe must be moving at all times to get a reading.



Q.10 A "spinning probe" would most likely be a (an):A. bobbin coil.B. ID coil.C. OD coil.D. probe coil.

Q.11 A "feed-through" coil is:A. a coil with primary/secondary windings connected so that the signal is fed through the primary to the secondary.B. an encircling coil.C. an OD coil.D. both B and C.

Q.12 When inspecting a tubular product with an encircling coil, which statement is not true?A. OD discontinuities can be found.B. Axial discontinuity locations can be noted.C. Circumferential discontinuity locations can be noted.D. ID discontinuities can be found.



Q.13 An absolute coil measurement is madeA. by comparing one spot on the test object to another.B. without reference to or direct comparison with a standard.C. only with probe coils.D. by comparative measurement to a known standard.

Q.14 When coils in a differential arrangement are affected simultaneously with the same test object variables, the output signalA. is directly proportional to the number of variables.B. is "0" or near-"0."C. is indirectly proportional to the number of variables.D. is primarily a function of the exciting current.

Q.15Which coil type inherently has better thermal stability?A. BobbinB. AbsoluteC. ODD. Differential



Q.16 A hybrid coil is composed of two or more coils. The coils -A. must be aligned coplanar to the driver axis.B. may be of widely different dimensions.C. must be impedance-matched as closely as possible.D. are very temperature sensitive.

Q.17 Proper selection of test coil arrangement is determined by:A. shape of test object.B. resolution required.C. sensitivity required.D. all of the above.

Q.18 A coil's resistance is determined by:A. wire material.B. wire length.C. wire cross-sectional area.D. all of the above.



Q.19 Inductance is analogous to:A. force.B. volume.C. inertia.D. velocity.

Q.20 The unit of inductance is the:A. henry.B. maxwell.C. ohm.D. farad.



Level II Q&A

TWO


Level II – Q&A

1. A 2. D 3. A 4. B 5. D 6. A 7. D 8. B 9. A 10. C 11. C 12. B 13. A 14. C 15. D16. D 17. B 18. B 19. A 20. C 21. D 22. B 23. B 24. D 25. C

26. A 27. D 28. B 29. B 30. C 31. B 32. C 33. C 34. C 35. D 36. D 37. B 38. A 39. A 40. B 41. C 42. A 43. C 44. C 45. D 46. C 47. D 48. C 49. A 50. D

51. B 52. D 53. C 54. C 55. D 56. C 57. D 58. A 59. C 60. D 61. A 62. D 63. A 64. B 65. C 66. B 67. D 68. B 69. D 70. A 71. B 72. B 73. D 74. B 75. D

76. C 77. A 78. B 79. C 80. B 81. A 82. D 83. A 84. C 85. A 86. B 87. C 88. D 89. D 90. A 91. A 92. C 93. C 94. C 95. D 96. C 97. A 98. A 99. C 100. A

101. B 102. A 103. E 104. D

1. A method of minimizing the effect of indications caused by gradual dimensional changes while retaining the indications caused by discontinuities is to:A. Include a high pass filter in the eddy current test equipment 高通滤波器B. Include a low pass filter in the eddy current test equipmentC. Increase the band pass of the amplifierD. Use the impedance method of testing

2. Which of the following methods may be used to improve the signal to noise ratio of an eddy current test system?A. Filtering or differentiationB. Phase discriminationC. IntegrationD. All of the above

3. In order decrease the effect on conductivity readings due to variations in test 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 for decreasing this effect



High Pass Filter 高 “通” 滤波器

http://www.cchrispeters.com/SynthesisTerms/HighPassFilter.htm


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 coil

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 off

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 of the above


7. The fill factor when a 13 mm (0.5 in) diameter bar is inserted in a 25 mm (1 in) diameter coil is:A. 0.5 (50%)B. 0.75 (75%)C. 1.0 (100%)D. 0.25 (25%) η = (D1/D2)2 = (.5)2

8. The term used to define the difference between actual instrument output and expected output as defined by a straight line calibration curve is:A. Phase shiftB. NonlinearityC. Lift offD. Skin effect

9. Which of the following could be used to suppress unwanted high frequency harmonics?A. Low pass filterB. OscillatorC. Phase discriminatorD. High pass filter


10. 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 frequencies

11. The inductive reactance of a test coil can be calculated using the formula:A. XL = 2πLB. XL = 0.5πLC. XL = 2πfLD. XL = 1R

12. When conducting an eddy current test, variations in the test material can be detected as variations in:A. Test speedB. Impedance of a pickup coilC. None of the aboveD. All of the above


13. 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 an unbalance in the system is:A. DifferentialB. AbsoluteC. LaminarD. Flying probes

14. Tubing is generally inspected using:A. U shaped coilsB. Gap coilsC. Encircling coilsD. None of the above

15. When testing small parts in an eddy current encircling coil for permeability σmeasurements, 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 above


16. In a test coil consisting of both a primary and secondary winding, the voltage across the secondary is a function of:A. Test material permeabilityB. Test frequencyC. Geometry of the test objectD. All of the above

17. Eddy current testing relies on the principle of:A. MagnetostrictionB. Electromagnetic inductionC. Piezoelectric energy conversionD. Magnetomotive force

18. When the H field strength around a material is increased and then decreased to zero, the induction field B within the part does not return to zero. The term to define the B value when H has returned to zero is:A. Coercive forceB. Residual magnetism (retentivity, remanence)C. Saturation valueD. Hysteresis loss


Residual Magnetism – Retentivity, Remanence

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magperm.html


Coercivity and Remanence in Permanent MagnetsA good permanent magnet should produce a high magnetic field with a low mass, and should be stable against the influences which would demagnetize it. The desirable properties of such magnets are typically stated in terms of the remanence and coercivity of the magnet materials.

When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. The amount of magnetization it retains at zero driving field is called its remanence. It must be driven back to zero by a field in the opposite direction; the amount of reverse driving field required to demagnetize it is called its coercivity. If an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retraceability of the magnetization curve is the property called hysteresis and it is related to the existence of magnetic domains in the material. Once the magnetic domains are reoriented, it takes some energy to turn them back again. This property of ferrromagnetic materials is useful as a magnetic "memory". Some compositions of ferromagnetic materials will retain an imposed magnetization indefinitely and are useful as "permanent magnets".

The table below contains some data about materials used as permanent magnets. Both the coercivity and remanence are quoted in Tesla, the basic unit for magnetic field B. The hysteresis loop above is plotted in the form of magnetization M as a function of driving magnetic field strength H. This practice is commonly followed because it shows the external driving influence (H) on the horizontal axis and the response of the material (M) on the vertical axis. Besides coercivity and remanence, a quality factor for permanent magnets is the quantity (BB0/μ0)max. A high value for this quantity implies that the required magnetic flux can be obtained with a smaller volume of the material, making the device lighter and more compact.


The alloys from which permanent magnets are made are often very difficult to handle metallurgically. They are mechanically hard and brittle. They may be cast and then ground into shape, or even ground to a powder and formed. From powders, they may be mixed with resin binders and then compressed and heat treated. Maximum anisotropy of the material is desirable, so to that end the materials are often heat treated in the presence of a strong magnetic field.

The materials with high remanence and high coercivity from which permanent magnets are made are sometimes said to be "magnetically hard" to contrast them with the "magnetically soft" materials from which transformer cores and coils for electronics are made.

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magperm.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/solids/magperm.html


Rare Earth MagnetsThe permanent magnets which have produced the largest magnetic flux with the smallest mass are the rare earth magnets based on samarium and neodymium. Their high magnetic fields and light weight make them useful for demonstrating magnetic levitation over superconducting materials.

The samarium-cobalt combinations have been around longer, and the SmCo5 magnets are produced for applications where their strength and small size offset the disadvantage of their high cost. The more recent neodymium materials like Nd2Fe14B produce comparable performance, and the raw alloy materials cost about 1/10 as much. They have begun to find application in microphones and other applications that exploit their high field and light weight.

The production is still quite costly since the raw alloy must be ground to powder, pressed into the desired shape and then sintered to make a durable solid.



δμσ∝∞∙ωΩπθ√ρφ°≤ewwwwwww


19. The term used to define the value of H field required to decrease the remanence of a material to zero is:A. Coercive forceB. Magnetizing forceC. Back emfD. The overlap value

20. The three major specimen parameters that influence eddy current testing are:A. Electrical conductivity, frequency, and material geometryB. Density, permeability, and frequencyC. Electrical conductivity, permeability, and material geometryD. Thermal conductivity, electrical conductivity, and permeability

21. Doubling the number of turns on a coil will:A. Double the inductanceB. Halve the inductanceC. Decrease the inductance by a factor of fourD. Increase the inductance by a factor of four L= (μ0μrN2A)/l


21. Doubling the number of turns on a coil will:A. Double the inductanceB. Halve the inductanceC. Decrease the inductance by a factor of fourD. Increase the inductance by a factor of four

L= (μ0μrN2A)/l , L= (μN2A)/l


Self Inductance of a CoilInductance is the name given to the property of a component that opposes the change of current flowing through it and even a straight piece of wire will have some inductance. Inductors do this by generating a self-induced emf within itself as a result of their changing magnetic field.When the emf is induced in the same circuit in which the current is changing this effect is called Self-induction, ( L ) but it is sometimes commonly called back-emf as its polarity is in the opposite direction to the applied voltage.

When the emf is induced into an adjacent component situated within the same magnetic field, the emf is said to be induced by Mutual-induction, ( M ) and mutual induction is the basic operating principal of transformers, motors, relays etc. Self inductance is a special case of mutual inductance, and because it is produced within a single isolated circuit we generally call self-inductance simply, Inductance.

The basic unit of measurement for inductance is called the Henry, ( H ) after Joseph Henry, but it also has the units of Webers per Ampere ( 1 H = 1 Wb/A ).Lenz’s Law tells us that an induced emf generates a current in a direction which opposes the change in flux which caused the emf in the first place, the principal of action and reaction. Then we can accurately define Inductance as being: “a coil will have an inductance value of one Henry when an emf of one volt is induced in the coil were the current flowing through the said coil changes at a rate of one ampere/second”.In other words, a coil has an inductance, ( L ) of one Henry, ( 1H ) when the current flowing through it changes at a rate of one ampere/second, ( A/s ) inducing a voltage of one volt, ( VL ) in it. This mathematical representation of the rate of change in current through a coil per unit time is given as:…….Read more on: http://www.electronics-tutorials.ws/inductor/inductance.html

Inductance (measured in henry) is an effect which results from the magnetic field that forms around a current carrying conductor. Current flowing through the inductor creates a magnetic field which has an associated electromotive field which opposes the applied voltage. This counter electromotive force (emf) is generated which opposes the change in voltage applied to the inductor and current in the inductor resists the change but does rise. This is known as inductive reactance. It is opposite in phase to capacitive reactance. Inductance can be increased by looping the conductor into a coil which creates a larger magnetic field…….Read more on http://www.raftabtronics.com/TECHNOLOGY/ElectromagneticBasics/InductorBasics/tabid/109/Default.aspx

Basic inductance formula:

L = (μN2A)/l = (μ0μrN2A)/lWhere:L = Inductance in henriesμ0 = permeability of free space = 4π × 10-7 H/mμr = relative permeability of core materialN = number of turnsA = area of cross-section of the coil in square metres (m2)l = length of coil in metres (m)

http://www.raftabtronics.com/TECHNOLOGY/ElectromagneticBasics/InductorBasics/tabid/109/Default.aspx


22. Frequency ratio, f/fg, can be defined as:A. The argument of the mathematical function describing the electromagnetic field

within the test specimenB. Test frequency divided by limit frequencyC. Neither of theseD. Both of these

23. When testing tubing, using an encircling (OD) 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. Indeterminate

24. A term used to define an instrumentation technique that discriminates between variables in the test part by the different phase angle changes which these conditions produced in the test signal is:

A. Phase distortionB. Phase shiftingC. Phase discriminationD. Phase analysis


Note: Subsurface indication lag the near surface indication, (as it’s signal comes later to show up).


Phase Analysis – OD & ID Phase Angles

http://innospection.com/pdfs/Eddy%20Current%20Theory.pdf


In eddy current testing, what is impedance plane analysis?Impedance plane analysis or phase analysis is used because the signals generated in an eddy current test are vector and not scalar quantities. That is to say, they are properly described by two quantities, their amplitude and phase rather than just by their amplitude. Phase analysis of the test signal using a cathode ray oscilloscope or LCD screen instead of mere amplitude measurements with a meter allows a greater level of differentiation between relevant signals and unwanted noise. The effect of eddy currents on the coil impedance is described on the impedance plane diagram.Eddy currents have surprisingly well ordered effects on the amplitude and phase of coil voltages. Thanks mainly to the efforts of Dr Forster in the immediate post-war years, these effects have been rationalised using mathematics. Computers can now be used with a good level of accuracy to predict eddy current test responses to simulated defects.

http://www.twi-global.com/technical-knowledge/faqs/ndt/faq-in-eddy-current-testing-what-is-impedance-plane-analysis/


Phase Lag Phase lag is a parameter of the eddy current signal that makes it possible to obtain information about the depth of a defect within a material. Phase lag is the shift in time between the eddy current response from a disruption on the surface and a disruption at some distance below the surface.

The generation of eddy currents can be thought of as a time dependent process, meaning that the eddy currents below the surface take a little longer to form than those at the surface. Disruptions in the eddy currents away from the surface will produce more phase lag than disruptions near the surface. Both the signal voltage and current will have this phase shift or lag with depth, which is different from the phase angle discussed earlier. (With the phase angle, the current shifted with respect to the voltage.)

Note: Subsurface indication lag the near surface indication, (as it comes later to show up).

https://www.nde-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/phaselag.htm


Phase lag is an important parameter in eddy current testing because it makes it possible to estimate the depth of a defect, and with proper reference specimens, determine the rough size of a defect. The signal produced by a flaw depends on both the amplitude and phase of the eddy currents being disrupted.

A small surface defect and large internal defect can have a similar effect on the magnitude of impedance in a test coil [ standard depth, δ = (πfμσ) -½ , intensity at depth jx =jo∙e –x/δ ].

However, because of the increasing phase lag with depth, there will be a characteristic difference in the test coil impedance vector.Phase lag can be calculated with the following equation. The phase lag angle calculated with this equation is useful for estimating the subsurface depth of a discontinuity that is concentrated at a specific depth. Discontinuities, such as a crack that spans many depths, must be divided into sections along its length and a weighted average determined for phase and amplitude at each position below the surface.

θ = x/ δ where: x = depth, δ = standard depth



At one standard depth of penetration, the phase lag is one radian or 57º. This means that the eddy currents flowing at one standard depth of penetration (δ) below the surface, lag the surface currents by 57º. At two standard depths of penetration (2δ), they lag the surface currents by 114º. Therefore, by measuring the phase lag of a signal the depth of a defect can be estimated. On the impedance plane, the liftoff signal serves as the reference phase direction. The angle between the liftoff and defect signals is about twice the phase lag calculated with the above equation. As mentioned above, discontinuities that have a significant dimension normal to the surface, will produce an angle that is based on the weighted average of the disruption to the eddy currents at the various depths along its length.

In the applet below, the relationship between the depth and dimensions of a discontinuity and the rotation produced on the impedance plane is explored. The red lines represent the relative strength of the magnetic field from the coil and the dashed lines indicate the phase lag of theeddy currents induced at a particular depth.



25. If the characteristic frequency (fg) of a material is 125 Hz, the test frequency required to give an f/fg ratio of 10 would be:A. 1.25 HzB. 12.5 HzC. 1.25 kHzD. 12.5 kHz


More Reading on Phase Analysis

http://eddy-current.com/another-thing-not-so-easy-about-eddy-current-testing-of-tubes/


Another inconvenience that arises during the eddy current testing of heat exchanger tubes is that although phase analysis (measuring defect depth based on the angle on the screen) is usually the best measure of a defect’s depth, it is not perfect.The two eddy current screens shown in the diagram are a bit cluttered because you can see the dent and five defects of an ASME calibration tube that we’ve used for examples in previous articles. The green horizontal signal is, of course, the dent signal. Then, rotated clockwise from this at about 45 degrees, are the through wall hole, followed by the 80, 60, 40, and 20 per cent O.D. pits, all of similar amplitude.

http://eddy-current.com/another-thing-not-so-easy-about-eddy-current-testing-of-tubes/


More Reading on Phase Analysis – Flaw Angles

http://www.ndt.net/apcndt2001/papers/224/224.htm


More Reading on Phase Analysis – Flaw Depths


?


More Reading on Phase Analysis – Flaw Length



Level II – Q&A





101. B 102. A 103. E 104. D


26. A term used to define any change in a sinusoidal signal when the output is not a linear reproduction of the input is:A. DistortionB. LinearityC. Phase shiftingD. Dynamic range

27. At a fixed test frequency, in which of the following materials will the eddy current penetration, be greatest?A. Aluminum (35% IACS conductivity)B. Brass (15% IACS conductivity)C. Copper (95% IACS conductivity)D. Lead (7% IACS conductivity)

28. The heating effect in magnetic material caused by the work required to rotate magnetic domains (AC?) can be eliminated by:A. Increasing the rate of displacement of the specimen through the coilB. Magnetically saturating the test specimenC. Decreasing the rate of displacement of the test specimen through the test coilD. Testing in an air conditioned room


Magnetic Domain – Hysteresis Curve


29. 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 above

30. 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 above

Note on Q30 – The impedance increase similar to lift off effect. The impedance variation by a given change in σ decrease, due to reduce sensitivity by the lift off effect.


31. The abscissa values on the impedance plane shown in Figure 2 are given in terms of:A. Absolute conductivityB. Normalized resistanceC. Absolute inductanceD. Normalized inductance


32. In Figure 2 (an impedance diagram for solid nonmagnetic rod), the fg or characteristic frequency is calculated by the formula:A. fg= σμ/d²B. fg= δμ/dC. fg= 5060/σμd²D. fg= R/L

33. 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 the

coilD. No change in the phase or magnitude of the voltage across the coil


34. In Figure 3, the solid curves are plots for different values of:A. Heat treatmentB. ConductivityC. Fill factorD. Permeability


35. 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 above


Figure 4

Charlie C

hong/ Fion Zhang

Figure 4


36. 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 flaws

37. The magnetic domains in an un-magnetized ferromagnetic material are:A. Arranged to facilitate the conduction of electronsB. Randomly oriented and neutralize each otherC. Uniformly orientedD. Create a major north and south pole in the material


38. When a magnetic material is placed in a region of an applied magnetizing force (H), magnetic field (B) is developed in the material by means of:A. InductionB. ConductionC. Heat transferD. Magnetic domain transfer

39. Figure 5 illustrates the fact that the limit frequency, fg, equations and impedance diagrams for long solid rods and long thin walled tubing are:A. DifferentB. IdenticalC. SimilarD. Unrelated

40. To eliminate any dependence upon the number of turns of a test coil, the inductance values of an impedance diagram are:A. DisregardedB. NormalizedC. Corrected to a value of 1D. None of the above


Figure 4

Charlie C

hong/ Fion Zhang

Figure 5

Charlie C

hong/ Fion Zhang

ωLo = Eo, for ωL = Eimg, R = Ereal


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) can be calculated precisely from Eq. (3.2):

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∙ d 2) (3.2)

Where:d= solid rod diameter

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


41. A term used to define a system that indicates only the magnitude of variations in the total coil impedance regardless of the phase or direction in which it occurs on an impedance plane is:A. Inductive reactance magnitude systemB. Feedback controlled systemC. Impedance magnitude systemD. Impedance vector analysis system

42. When eddy current testing tubing with a system that includes a frequency discriminating circuit, which of the following variable would b classified as high frequency variable?A. Small discontinuitiesB. Conductivity changesC. Diameter changesD. Wall thickness variations

43. A major problem associated with the eddy current test method is the:A. Inability of eddy current testing to accurately measure conductivityB. Need to test at low speeds to prevent skippingC. Large number of known and unknown variables that appear in the output indicationD. Inability of eddy current testing to detect small discontinuities


44. The atoms of a metal showing magnetic characteristics are grouped into regions that are the smallest known permanent magnets. The regions are called:A. Lattice structuresB. CellsC. DomainsD. Planetary spins

45. When a coil’s magnetizing force is applied to a ferromagnetic material, 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 the resistivityC. The same as the flux density generated by the test coilD. Greater than the flux density generated by the test coil

46. The Flux density in a magnetic material is usually designated by the:A. Symbol μB. Symbol σC. Letter BD. Letter H


47. The magnetizing force of an eddy current test coil is usually designed by the:A. Symbol μB. Symbol σC. Letter BD. Letter H

48. In eddy current testing, the specimen is coupled to the test coil by:A. Core couplingB. Magnetic saturationC. The coil’s magnetic fieldD. Magnetic domains

49. The thickness of nonconductive 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 test


50. The use of magnetic shielding around the exciting coil will generally:A. Increasing the magnetic field extension but decrease the eddy current

penetrationB. Increase the magnetic field extension and eddy current penetrationC. Decrease the magnetic field extension but increase the eddy current

penetrationD. Decrease the magnetic field extension and eddy current penetration

eddy current

magnetic field extension


Shielded and unshielded probes Probes are normally available in both shielded and unshielded versions; however, there is an increasing demand for the shielded variety. Shielding restricts the magnetic field produced by the coils to the physical size of the probe or even less. A shield can be made of various materials, but the ones mostly used are: ferrite (like a ceramic made of iron oxides), Mumetal®, and mild steel.

Ferrites make the best shields because they provide an easy path for the magnetic field but have poor conductivity. This means that there are few eddy current losses in the shield itself. Mild steel has more losses but is widely used for spot probes and ring probes due to its machinability and when ferrites are not available in certain sizes or shapes. Mumetal® is used sometimes for pencil probes as it is available in thin sheet; however, it is less effective than ferrite. Shielding has several advantages: first, it allows the probe to move in (or close to) geometry changes, such as edges, without giving false indications; next, it allows the probe to touch ferrous fastener heads with minimal interference; last, it allows the detection of smaller defects due to the stronger magnetic field concentrated in a smaller area. On the other hand, unshielded probes allow somewhat deeper penetration due to the larger

magnetic field. They are also slightly more tolerant to lift-off. Unshielded probes are recommended for the inspection of ferrous materials (steel) for surface cracks, andin particular with meter instruments. The reason for this is that the meter responseis too slow to allow the signal from a shielded probe to be displayed at normal

scanning speeds due to the smaller sensitive area.

http://www.olympus-ims.com/en/resources/white-papers/eddy-current-probes-and-application-guide/


Level II – Q&A





101. B 102. A 103. E 104. D


51. Which of the following is not a factor that affects the inductance of an eddy current test coilA. Diameter of coilsB. Test frequency L=μoN2A/lC. Overall shape of the coilsD. Distance from other coils

52. The formula used to calculate the impedance of an eddy current test coil is: D

53. 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 coilD. Exists only in the test specimen


Inductance The increasing magnetic flux due to the changing current creates an opposing emf in the circuit. The inductor resists the change in the current in the circuit. If the current changes quickly the inductor responds harshly. If the current changes slowly the inductor barely notices. Once the current stops changing the inductor seems to disappear.

http://sdsu-physics.org/physics180/physics196/Topics/inductance.html

Charlie Chong/ Fion Zhang http://sdsu-physics.org/physics180/physics196/Topics/inductance.htmlhttp://sdsu-physics.org/physics180/physics196/Topics/images_196/32_ind1.swf

RL Circuit


RL Circuit

http://sdsu-physics.org/physics180/physics196/Topics/inductance.htmlhttp://sdsu-physics.org/physics180/physics196/Topics/images_196/32_ind2.swf

Charlie Chong/ Fion Zhang http://sdsu-physics.org/physics180/physics196/Topics/inductance.htmlhttp://sdsu-physics.org/physics180/physics196/images_196/32_oscillation2.swf

Oscillation in LC Circuit


54. A term used to define an eddy current test coil which uses magnetic material to purposely shape the magnetic field is:A. Bobbin coilB. Encircling coilC. Spinning coilD. Gap coil

55. A term used to define an eddy current test coil which uses magnetic material to purposely shape the magnetic field is:A. Bobbin coilB. Encircling coilC. Spinning coilD. Gap coil Gap Coil ≡ horse shoe coil?

56. The vector point, ellipse, and linear time base methods are all subdivisions of the:A. Impedance method of testingB. The modulation analysis method of testingC. The phase analysis method of testingD. None of the above


57. It is frequently possible to separate the conductivity variable from the permeability and dimensional variables when using:A. The vector point method of testingB. The ellipse method of testingC. The linear time base method of testingD. Any of the above methods of testing

58. When eddy current testing by the ellipse method, the normal indication when the test specimen and reference standard are the same is approximately:A. A straight horizontal line on a cathode ray tubeB. An ellipse on a cathode ray tubeC. A null reading on a meterD. A clean base line on a strip chart

59. When eddy current testing by the ellipse method, one variable may be indicated by the angle of the ellipse or straight line while another variable may be indicated by the:A. Brightness of the ellipseB. Horizontal length of the straight lineC. Size of the ellipse openingD. Sinusoidal shape of the waveform

→


60. When eddy current testing by the linear time base method, _________ is applied to the vertical deflection plates of a cathode ray tube when the test specimen and reference standard are the same and the balance controls are properly adjusted.A. A sinusoidal wave in phase with the timing voltageB. A sinusoidal wave 90 degrees out of phase with the timing voltageC. A sawtooth waveformD. Zero net voltage

61. When eddy current testing by the linear time base method, what is applied to the vertical deflection plates of the cathode ray tube when a condition of unbalance exists between the test specimen and the reference standard?A. A sinusoidal waveB. A sawtooth waveC. A squarewaveD. No voltage

62. The conductivity value for a metal is a function of the:A. Heat treatment give the metalB. Cold working performed on the metalC. Aging process used on the metalD. All of the above


63. The ratio of the specific diameter of a probe to the minimum discontinuity of interest should be:A. Less than 2B. Greater than 2C. Greater than 4D. Greater than 10

64. Which of the following materials would be more likely used as a mounting material for a probe coil?A. AluminumB. FiberglassC. CopperD. Steel

65. A term used to define a surface or internal rupture that is attributed to processing at too low a temperature or excessive working or metal movement during the forging, rolling, or extruding operation is:A. A cold shutB. MicroshrinkageC. BurstD. An inclusion


66. A term used to define the timing relationships involved in alternating current signals is:A. MagnitudeB. PhaseC. ImpedanceD. Reactance

67. When eddy current testing a nonferrous material, the choice of test frequency is determined by the:A. Degree of phase discrimination required θ = x/δB. Eddy current penetration needed δ = (πfμσ) -½

C. Rate of response requiredD. All of the above

68. When testing ferrous materials, a small but detectable portion of the magnetic flux in the material will pass outside the metal when a surface discontinuity is encountered. This flux is called:A. Air fluxB. Leakage fluxC. Induced fluxD. None of the above


69. A term used to define a property of a test system which enables the separation of signals due to discontinuities in the test specimen that are located in close proximity to each other is:A. Dynamic rangeB. SensitivityC. LinearityD. Discontinuity resolution

70. A term used to define a material having a permeability less than that of a vacuum is:A. DiamagneticB. FerromagneticC. ParamagneticD. Magnetic

71. The inductive reactance of a coil is measured in units of:A. MhosB. Ohms XL= ωLC. HenrysD. Gauss


72. Which of the following coil arrangements would eliminate or decrease the effects of minor variations in diameter, chemical composition, harness, etc., which occur gradually along the length of a wire?A. External reference differentialB. Self comparison differentialC. Single coil absoluteD. Double coil absolute

73. Which of the following conditions are not important when selecting specimens to be used as reference standards?A. The specimen should be of the same size and shape as the piece to be testedB. The specimen should have the same heat treatmentC. The surface finish of the specimen should be the same as the piece to be testedD. If the material is aluminum, the surface should be anodized


74. An eddy current test coil’s magnetic field intensity in air:A. Increase 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 coil

75. The circuits which make it possible to minimize the effects of signals caused by variables of no interest on the read out mechanism are based on differences in:

A. AmplitudeB. PhaseC. FrequencyD. Any one or a combination of the quantities listed above


Level II – Q&A





101. B 102. A 103. E 104. D


76. When a nonmagnetic rod is placed inside an eddy current test coil:A. The magnetic field generated by the coil is increased in intensityB. The distribution of eddy current is uniform through the rod’s across sectionC. The distribution of eddy currents is 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 decreases

77. The symbol commonly used to signify impedance is:A. ZB. XjεC. RD. Xc

78. A decrease in conductivity is equivalent to:A. An increase in permeabilityB. An increase in resistivity R = ρl/A , σ = 1/ρC. A decrease in permeabilityD. A decrease in resistivity


79. If the conductivity of a test part in an eddy current test coil decreases, the magnitude of the eddy currentsat a given depth in the test specimen:A. IncreasesB. Remains the sameC. DecreaseD. May increase or decrease

80. When the voltage applied to a circuit and the current though the circuit both reach their maximums and minimums at the same time, the voltage and current are:A. AdditiveB. In phaseC. RegenerativeD. Out of phase

81. Which of the following is not a commonly used eddy current testing readout mechanism?A. Signal generatorB. MeterC. Cathode ray tubeD. Strip chart recorder


82. Which of the following materials would have the highest resistivity value?A. Aluminum with a 42% IACS ratingB. Magnesium with a 37% IACS ratingC. Cast steel with a 10.7% IACS ratingD. Zirconium with a 3.4% IACS rating


83. The two voltages (V1 and V2) shown in figure 6 are:A. In phaseB. 45 degrees out of phaseC. 90 degrees out of phaseD. 180 degrees out of phase


84. The two voltages (V1 and V2) in figure 7 are:A. In phaseB. 45 degrees out of phaseC. 90 degrees out of phaseD. 180 degrees out of phase


85. In figure 8, H represents:A. The coil’s magnetizing forceB. The material’s flux densityC. The material’s permeabilityD. The material’s conductivity

86. In figure 8, B represents:A. The coil’s magnetizing forceB. The material’s flux densityC. The material’s permeabilityD. The material’s conductivity

87. In figure 8, the distance represented by A is a measure of the material’s:A. PermeabilityB. ConductivityC. Residual magnetismD. Coercive force


88. In figure 8, the distance represented by C is a measure of the material’s:A. PermeabilityB. ConductivityC. Residual magnetismD. Coercive force

89. The ratio of a material’s flux density to a test coil’s magnetizing force, (B/H), can be used to determine the material’s:A. ConductivityB. ResistivityC. Lift offD. Permeability

90. 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 induce the eddy currents


91. 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 capacitance

92. For age hardenable aluminum and titanium alloys, change in hardness are indicated by changes in:A. RetentivityB. PermeabilityC. ConductivityD. Magnetostriction

93. The penetration of eddy currents in a conductive material is decreased when:A. Test frequency or conductivity of the specimen is decreasedB. Test frequency is decreased or conductivity of the specimen is increasedC. Test frequency, conductivity of the specimen, or permeability of the specimen are increased δ = (πfσμ) -½D. Permeability of the specimen is decreased


95. When testing magnetic materials in an AC field, increasing the field strength, (H?)A. Has not effectB. Increases eddy current penetrationC. Decreases eddy current penetrationD. Decreases eddy current penetration to some minimum value, and then increases it to its maximum value when the specimen becomes magnetically saturated

δ = (πfσμ)-½


94. When electrical 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 degreesC. The direction of the eddy currents in the part also reversesD. The Eddy currents in the part remain the same

95. When testing magnetic materials in an AC field, increasing the field strength:A. Has not effectB. Increases eddy current penetrationC. Decreases eddy current penetrationD. Decreases eddy current penetration to some minimum value, and then increases it to its maximum value when the specimen becomes magnetically saturated

δ = (πfσμ)-½


96. Impedance diagrams have been mathematically derived and experimentally verified for materials of any conductivity and permeability having rectangular, cylindrical, or spherical symmetry. To test all specimens of similar geometry under the same condition, it is only necessary to choose a test frequency, f, so that frequency ratio f/fg lies at the same point on the impedance diagram for each specimen. This principle is based upon:A. Ohm’s lawB. Kirchoff’s lawC. The similarity lawD. None of the above


97. To be useful, limit frequency equations must be:A. Used with their impedance diagramsB. Used to determine their impedance diagramsC. Both of theseD. Neither of these

98. 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 above

99. The term fill factor applies to:A. A surface coilB. Coaxial cableC. An encircling coilD. All of the above


100. 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 defect causeD. Pass rejectable material

101. Two test coils are often used in a bridge circuit to:A. eliminate skin effectB. Determine the difference between a known standard sampleC. Increase the conductivity of the circuitD. Decrease the system sensitivity

102. In inspecting ferromagnetic materials, relatively low frequencies are normally used because of the:A. Low penetrability of these materialsB. Higher resolutionC. Lower resolutionD. Higher penetrability of these materials


103. The actual frequencies used in any specific eddy current inspection should be selected on the bases of the:A. Thickness of the materialB. Desired depth of penetrationC. Degree of sensitivity or resolution requiredD. Purpose of the inspectionE. All of the above

104. In modulation analysis testing, which of the following would not modulate the test frequency applied to the test coil?A. Discontinuities in the test specimenB. Dimension changes of the test specimenC. Chemical composition of the test specimenD. A filter in the test circuit


Level III Q&A

Three


Level III – Q&A

1. b 2. c 3. d 4. b 5. c 6. d 7. b 8. b 9. c 10. b 11. b 12. b 13. b 14. c 15. d 16. b 17. d 18. b 19. d 20. b 21. c 22. d 23. b 24. c 25. a

26. a 27. e 28. b 29. d 30. e 31. a 32. a 33. b 34. a 35. b 36. b 37. c 38. a 39. e 40. d 41. d 42. c 43. e 44. d 45. c 46. c 47. a 48. c 49. b 50. a

51. b 52. d 53. b 54. c 55. c 56. d 57. a 58. c 59. a 60. d 61. c 62. c 63. b 64. a 65. c 66. d 67. b 68. d 69. a 70. a 7 1. c 72. c 73. d 74. b 75. b

76. b 77. c 78. b 79. d


Q1. In a feedthrough encircling coil eddy current system, what would be thepurpose of running a calibration defect several 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 speed

Q2. In a feedthrough encircling coil eddy current system, a calibration standard may be used to:a. insure repeatability and reliability of the setupb. calibrate the approximate depth of detectable flawsc. both a and bd. measure the test frequency


Q3. A calibration standard may be used with a spinning probe eddy current instrument to:a. produce an indication relative to the depth of the flawb. check the instrument for repeatability and freedom from driftc. check probe coil for possible damaged. all of the above

Q4. Spinning probe-type eddy current instruments are most useful in:a. detection of surface and subsurface inclusionsb. detection of surface defects such as overlaps and seamsc. detection of internal piping or burstd. all of the above


Q5. A product can be viewed in terms of electrical, magnetic effects. A diameter change of the product in an encircling coil is:a. an electrical effectb. a conductivity effectc. a magnetic effectd. all of the above

Q6. In Figure 9, ac flowing through a primary coil set-up a magnetic field and causes a flow of eddy currents in the rod. The voltage of the secondary coil isdependent upon:a. these eddy currentsb. the primary coilc. the generatord. all of the above


Figure 9


Q7. Which of the following is not a method that may be used to improve the signal-to-noise ratio?a. change to a test frequency that will decrease the noiseb. increase the amplification of the test instrumentc. improve the fill factord. add filter circuits to the instrument

Q8. In eddy current testing, the theoretical maximum testing speed is determined by the:a. magnetic flux densityb. testing frequencyc. conveyor drived. test coil impedance


Q9. In eddy current testing of ferromagnetic materials, the desaturating field may be provided by:a. an encircling solenoidb. a magnetic yokec. both a and bd. none of the above

Q10. Which of the following is a property of eddy currents induced in a conductor by an encircling coil?a. the magnitude of eddy current flow is large compared to the current flow in the coilb. the eddy current flow is affected by permeability variations in the samplec. the eddy current flow dissipates no power in the conductord. none of the above


Q11. Which of the following is a property of eddy currents induced in a homogeneous 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 axis

Q12. Which factor does not affect the phase shift between the transmitted signal and the reflected signal for a reflection-type coil (assuming the part isnonferromagnetic)?a. the conductivity of the sampleb. the magnitude of the transmitted signalc. the thickness of the sampled. the presence of defects in the sample


Q13. Lift-off certainly reduces the amplitude of the flux leakage signal. The other significant effect it has on the signal is a change in:a. phaseb. frequencyc. increasing lift-off which reduces the apparent width of the defectd. none of the above

Q14. The tubular product parameter having the greatest influence on the flux density of the magnetic field in the part (assuming the magnetizing force, H, remains constant) is the:a. surface roughness of the productb. diameter of the productc. wall thickness of the productd. length of the product


15. Any handling of equipment used in an eddy current system must take into consideration:a. the operator's abilitiesb. the use of the product being testedc. speed, frequency of test, sorting speed, and physical control of the productd. all of the above

16. An eddy current system lends itself to quality ratings such as "Quality Numbers" where the product being inspected:a. is not defectiveb. does not allow defective areas to be removedc. is of inferior qualityd. has inconsistent quality


17. When inspecting material with eddy currents in an automatic handling system, it is advisable to calibrate and adjust the sensitivity levels to:a. some electronic sourceb. another NDT methodc. an NBS standardd. an actual test part being inspected

18. A distinct advantage of using handling equipment in an eddy current test system is to reduce the error caused by:a. instrument driftb. lift-offc. skin effectd. all of the abovee. none of the above


19. Decreased coupling or fill factor results in decreased test sensitivity because:a. reduced coupling between the driver coil and the specimen induces less eddy current flow in the specimenb. reduced coupling between the specimen and the pickup coil results in smaller voltages across the pickup coilc. electrical circuits designed to provide fill factor compensation may prove to be inadequate, depending upon the extent of fill factor lossd. all of the above

20. 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 tester output signal changes that are not relevant to conditions within the specimen to be testedc. a fill factor or lift-off change will shift the operating frequencyd. to minimize the load on the constant current ac excitation circuits


21. The reactance component is decreased by placing a conducting object in the 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 degrees with the primary fieldc. the phase angle between the two field components is always greater than 90 degrees which partially cancels the primary fieldd. the secondary field is 180 degrees out of phase with the primary field which causes a large phase shift

Charlie C

hong/ Fion Zhang


22. Test coils may be shielded with conducting material or magnetic material to:a. shape fieldb. increase sensitivityc. increase resolutiond. all of the abovee. none of the above

23. When a magnetic bar is placed in the coil's electromagnetic field, thecoil's reactance is increased. What causes this phenomena?a. the coil becomes magnetically saturatedb. the permeability raises the inductance of the test coilc. the magnetic test sample's conductivity increases the reactance value of the coild. this effect is described mathematically by the equation μ = B/H


24. When an excitation voltage is applied to a primary winding, only themagnetic flux is in phase and the secondary magnetic flux is minor. 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. the insertion of the test object intensifies the secondary magnetic flux producing a new total magnetic flux which can be used to supply testinformationd. by subtracting the primary voltage from the secondary voltage, the net voltage is obtained


25. The test coil excitation current should be held constant so that the testpiece information obtained by an eddy current system will:a. contain only flaw information and not indicate variations in magnetic field strengthb. not contain signals generated by cross talkc. not contain electrical noised. all of the above

26. Eddy currents flowing in the test object at any depth produce magneticfields at greater depths, which oppose the primary field, thus reducing itseffect and causing what kind of change in current flow as depth increases?a. a decreaseb. an increasec. a frequency changed. none of the above


27. 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 hardness (affect conductivity?)d. test piece permeabilitye. all of the above

δ = (πfμσ) -½

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


28. Which of the following is not a common undesirable effect to the test coilcaused by the testing environment?a. temperature variationb. crack in test samplec. test object making contact with test coild. foreign object in the test coil fielde. test coil vibration

29. There is one function that responds to variations in eddy current flaw andmagnetic field conditions. This function actually produces the output signalfrom the coil. What is this function?a. phasingb. resistancec. reactanced. impedance


30. 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, coil resistanceb. coil inductance onlyc. coil resistance and inductance onlyd. frequency and coil resistance onlye. frequency and coil inductance only

XL = ωL


31. An ac current produces eddy currents in a test object. The vector Hprepresents the secondary ac field in the test piece. what function occurs toproduce a workable test situation? (See Figure 10.)a. changes in the test specimen such as a crack, metallurgical or dimensional change alter the secondary field phase and amplitudeb. the primary ac 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 output


32. 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. 100e. 150

Figure 11


33. Thin-walled tubes should be tested for cracks, alloy or wall thickness at frequency ratios between (see Figure 12):a. 0.1 and 0.4b. 0.4 and 2.4c. 2.4 and 4.0d. 4.0 and 10

Figure 12


34. Figure 13 indicates that the largest eddy current indications fromsubsurface cracks will occur when the frequency ratio (f/fg) is:a. 5 or lessb. 15c. 50d. 150 or more

Figure 13


35. 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 above


36. Figure 14 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. 50 and 100d. 100 and 150

Figure 14


37. An operating frequency of 100kHz will have the deepest penetration in:a. titaniumb. copperc. stainless steeld. Aluminum

δ = (πfσμ)-½

38. As the operating frequency is increased, the impedance of the empty coil:a. increasesb. decreasesc. remains the samed. none of the above

XL = 2πfL


39. Disadvantages of using a surface probe coil for the inspection of small diameter tubing include: a. inability to detect small discontinuities b. slow inspection speedc. inherent mechanical problemsd. both a and ce. both b and c


40. Differential coil systems can be of which of the following types? (see Figure 15)a. sketch no. 1b. sketch no. 2 (reflection differential coils)c. sketch no. 3d. all of the abovee. both a and b

Figure 15


41. The sensing element in an eddy current system can be which of the following?a. the secondary winding of a differential coilb. an absolute coilc. a single winding coild. all of the abovee. both a and b

42. Of the following test coil systems, which would be considered best for definitive detection of small discontinuities in tubing?a. encircling coilsb. inside probe (ID) coilsc. surface probe coilsd. both a and b


43. In a test coil system, when the sensing coil is placed near the excitationcoil, 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 test piecec. the arrangement is never sensitive to small discontinuitiesd. all of the abovee. both a and b


44. In linear time-base equipment:a. the balance control will not affect the phase of the signal on the CRTb. the balance control changes the horizontal position of the signal displayed on the CRTc. the phase control permits initial smoothing of the input signalsd. the phase control shifts the signal to the left or right on the CRT

45. Filters are used in modulation analysis to:a. amplify crack or other discontinuity signalsb. reduce the signal-to-noise ratioc. eliminate effect of small random changes in conductivity and permeability of test sampled. separate conductivity variations from permeability variations


46. In modulation analysis, the type of display usually used is:a. cathode ray tubeb. analog meterc. chart recorderd. digital voltmeter

47. When the slit technique is used with the linear timebase method:a. a shift in phase will move the waveform on the CRT to the left or rightb. after calibration, the waveform on CRT will move up or down when a discontinuity appearsc. the equipment can be adjusted so that permeability and conductivity changes will show little or no change in the slit valued. dimension effects will not be displayed at the slit. when the conductivity effect is on the horizontal line


48. In linear time-base equipment, which type of signal is applied to the horizontal deflection plates?a. sinusoidal voltageb. square-wave voltagec. sawtooth voltaged. amplitude-modulated sinusoidal voltage


49. In the ellipse method, the following (see Figure 16) indication should be interpreted as:a. change in dimensionb. change in conductivity and dimensionc. change in conductivityd. no change


50. The ellipse test method, used with feed through coils:a. can test rods, tubes, and wires for surface and subsurface cracksb. cannot be used for measuring diameter of rods that have surface cracksc. has limited value in the alloy sorting of nonferrous rodd. is not affected by lift-off variations


51. In cathode ray tube ellipse testing:a. a straight line trace will appear when the two voltages applied to the deflection plates are 90 degrees out of phaseb. the presence of a crack in a test specimen will generally produce a phase shiftc. changes in diameter of a rod cannot be separated from crack effectsd. a circle will appear on the screen whenever no voltage is applied to the vertical plates


Ellipse Methodthe display on the CRT will be a straightline.This condition indicates that there is an acsignal on the horizontal plates and zerodifferential voltage 'standard and test speci-men are the same) from the test coils onthe vertical plates.Now let's see what happens when we get a change in dimension. After all of our dis-cussion you probably expect to see an ellipse on the CRT - but not yet. A change indimension will just tilt the horizontal line asshown in this illustration.

NASA Nondestructive Testing Eddy Current Equipments Methods & Applications Volume-2


A dimension change will not noticably changethe phase of the signal on the test coil, but itwill give a difference in voltage.So now weno longer have a zero differential from thetest coil. We have a voltage difference, butthe test signal is still in phase with the signal on the horizontal plates.Thus ourstraight line remains straight but is inclined. A straight line results because, whentwo voltages having the same phase are applied simultaneously to thhorizontal andvertical plates of the CRT, a straight line will result.

Dimension change (tube diameter, thicknessor shape) will give an inclined straight line on the cathode ray tube.Suppose that rather than a dimension change we have a crack or discontinuity in thespecimen that gives us a conductivity change in the coil. Ah ha! Now we get an ellipse finally.



An ellipse is displayed on the cathode ray tube when the specimendiscontinuitygives a conductivity change in the coils. However, unlike the dimension change, wenow get a phase change on the signal to the vertical plates rather than a voltage change.This phase change causes the horizontal straight line to open up into an ellipse.

No Defect Conductivity Defect

Both Dimension &Conductivity Change


Small Change Large Change


52. Eddy current test instruments that indicate only the magnitude of variationin total impedance of the test coil are: (total impedance method?)a. unable to sort aluminum rods having different diameters, but the same chemical compositionb. normally used to measure wall thickness variations in as-cast pipe ?c. not used with cathode-ray tube indicatorsd. more sensitive to dimensional changes than variations in electrical conductivity (more sensitive to magnetic effects than electric effects)

53. When using an inspection system having an "ellipse display" readout, thesignal applied to the vertical input of the scope is related to that applied to thehorizontal input as follows:a. the vertical signal is demodulated; the horizontal signal is notb. the vertical and horizontal signals are of the same frequencyc. the vertical and horizontal signals are always in phased. none of the above


54. Which material should be selected to provide the most effective shielding of a test coil from an external RF field?a. fiberglassb. austenitic stainless steelc. copperd. Brass

55. To allow maximum current to flow through the coil, the capacitor should be adjusted so that:a. the capacitive impedance is equal to the generator impedanceb. the capacitive impedance is minimumc. the capacitive reactance is equal to the inductive reactanced. the capacitive impedance is maximum

Xc = 1/ωC, XL= ωL


56. 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 180 degree out-of-phase signal to the induced signalc. subtract an in-phase signal from the induced signald. any of the above

C.2-40, 2-41

C.* Eddy Current Testing, Classroom Training Handbook ( CT-6-5 ). San Diego, CA: General Dynamics/Convair Division. 1967. (Now published by The American Society for Nondestructive Testing, Inc.)


57. Which type of readout oscilloscope would be best for examining a nonrepetitive flaw indication during high speed testing?a. a storage typeb. a sampling typec. a type having a short persistance screend. a dual beam typeG.38.36

58. An ink-writing strip chart recorder generally provides an accurate representation of its input signal:a. if the signal frequency is 2 000 Hz or greaterb. if the signal frequency is at least 200 Hzc. if the signal frequency is limited to 20Hzd. only if the signal frequency is limited to 2 HzV.88


59. A probe coil inspection system is being used to detect cracks in bars. If the cracks have a minimum length of 6 mm (0.25 in.), reliable inspection is best achieved by making the coil diameter:a. 6 mm (0.25 in.)b. 13 mm (0.5 in.)c. any multiple of 6 mm (0.25 in.)d. coil diameter is irrelevantG.38.31

60. To ensure reliable flaw detection, the maximum velocity of tubing through an encircling coil must be limited. This limitation is determined by:a. the inspection coil lengthb. the desired flaw size resolutionc. the test frequencyd. all of the aboveC.4-29


61. Normal test speeds for modulation analysis testing is:a. 0-1.2 m (0-4 ft)/minb. 1.2-9 m ( 4-30 ft)/minc. 9-91 m (40-300 ft)/mind. 91-1219 m (400-4 000 ft)/minC.4-29

62. When performing modulation analysis testing, the type of test coil:a. must be of the differential typeb. must be of the absolute typec. can be any basic typed. a and b are the best answersC.4-29


63. A major limitation of modulation analysis is that the system is based on:a. static testsb. moving testsc. absolute coil arrangementsd. differential coil arrangementsC.3-26

64. Chemical composition, alloy changes, and heat treat changes usually have a frequency modulation that is:a. lowb. mediumc. highd. very highC.3-25


65. Modulation would be defined as:a. a process of comparing an instrument reading with a standardb. a process of grouping articles by their response to eddy currentsc. a process of applying a variable effect to something that is constantd. the point where increases in the coil's magnetizing force does not increase the material's flux densityD.S-116

66. In modulation analysis, the coil's excitation frequency is being modulated by:a. test article conductivityb. test article dimensionsc. test article defectsd. all of the aboveD.S-126


67. Impedance changes produced by small lift-off variations are greatest when:a. there is a nonconductive coating on the test materialb. the coil is usually in contact with the test materialc. lower test frequencies are usedd. large diameter coils are usedU.280

68. When testing for the unknown conductivity of a metal, the measured conductivity is strongly affected by:a. I2Rb. material thicknessc. coil diameterd. specimen temperatureV.78


69. 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 inductanceA.216

70. In developing a multifrequency test, the parameter separation limitations are greatest for those parameters producing:a. nearly similar signalsb. 0 degrees to 90 degrees phase shiftsc. signals having no electrical relationd. 90 degrees to 110 degrees phase shiftsA.216


71. Mutual inductance describes:a. the effect two coils have on each otherb. the coupling between the test coil and test partc. a and bd. none of the aboveR.29

72. Leakage flux testing is most applicable for the inspection of:a. shallow surface seams on finished roller bearingsb. heavy-wall copper tubingc. surface and subsurface cracks in hot-rolled rough surface ferromagnetic piped. soft spots on polished steel bar stockN.122


73. 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, depending upon the alloy and the nature of the heat treatmentG.42.19

74. Limit frequency, fg , is defined when the argument of the mathematical function describing the electromagnetic field within a test specimen is setequal to:a. 6.25b. 1c. 0.37d. 0G.36.13


75. Referring to Figure 17, suppose a test is being conducted at an f/fg ratio of 1. Due to a mix in alloys, a new test piece with a conductivity value fourtimes as great as the original material is inserted in the coil. The new f/fg ratio will be:a. 0.25b. 4c. 16d. unchangedS.l0l

Rod: fg = 5060/σμd2

Tube: fg = 5056/σdiwμ

Figure 17


76. Figure 18 illustrates that the separation of diameter effects and conductivity effects:a. can be accomplished at any f/fg Eb. can best be accomplished at f/fg larger than 4c. can best be accomplished at f/fg less than 4d. cannot he accomplished at any f/fg


Figu

re 1

8


77. Figure 19 illustrates:a. variations in fill factor for a solid rodb. variations in fill factor for a thin-walled tubec. transition between a solid rod and thin-walled tubed. all of the aboveG.38.9


Figu

re 1

9


78. Figure 20 illustrates the impedance diagram for tubing where the ratio ofthe inside diameter to outside diameter is 80 percent. It is possible tocalculate an approximate limit frequency, f , by using only the outsidediameter. Thus the maximum test sensitivity for effects of conductivity, wallthickness and cracks occurs at a frequency ratio of:a. 6.25b. 13c. 25d. 400G.38.11, 38.12

Charlie C

hong/ Fion Zhang

Figure 20


79. The electromagnetic field in a test specimen during eddy current testing is described by:a. Bessel functionsb. exponential functionsc. algebraic functionsd. all of these


Flux Leakage Testing Method


Level I Q&A-Flux Leakage Testing Method


Level I - Standard Answers1. c 2. a 3. e 4. c 5. c 6. b 7. d 8. a 9. c 10. d 11. a 12. b 13. d 14. d 15. d 16. d

17. a 18. d 19. d 20. e


1. In flux leakage testing of a ferromagnetic object, magnetized close to the saturation point using an encircling coil as a sensor, what is a primarycondition which needs to be met in order to obtain a response from the flaw?a. using a coil with a high number of turnsb. providing electrical connection between coil and tested objectc. moving the tested object in relation to the coild. shielding the cable which connects the coil with the recordere. using a strip chart recorderEE.62


2. What will be the relative flux leakage level on the surface of the I X 7 strandcable (Figure FL-1) caused by an outer wire break compared with that causedby an inner wire break? (Assume that the gap between the ends of brokenwire is the same in both cases.)a. greaterb. smallerc. the same, if diameters of both wires are the samed. the same, even if diameters of both wires are differentEE.63


3. What method of magnetization can be used in flux leakage testing?a. permanent magnetb. high frequency acc. dcd. a and be. a and cZ.43


4. Flux leakage may occur at a surface defect in a ferromagnetic material:a. when the magnetizing force is presentb. after the magnetizing force has been removedc. a and bd. none of the aboveZ.51

5.Flux leakage inspection can normally be applied to:a. ferromagnetic and nonmagnetic materialb. nonmagnetic materials onlyc. ferromagnetic materials onlyd. nonconductors onlyU.330


6. Rotational transverse magnetization in bar or pipe testing is used for the detection of:a. transverse defectsb. defects that have a longitudinal componentc. only longitudinal defectsd. both transverse and longitudinal defectse. only holesAA.16

transverse magnetization ≡ circumferential magnetization

Level II Q&A22. In the examination of tubular products, a circumferential (transverse)magnetic field can be established by:a. properly positioning north and south poles of a magnet with respect to the tubeb. using a central conductor positioned in the tubec. a and bd. neither a nor bDD.629


Rotational Transverse Magnetization by Coil

transverse magnetization ≡circumferential magnetization ≡ circular magnetization?

Pipe axis

B


7.With rotational flux leakage detection systems, distinctions between similar OD and ID defects are accomplished by:a. observing a difference in amplitudeb. measurement of impedance changec. observing the signal to noise ratiod. frequency analysise. only by visual observation of test pieceL.54


8. Using Figure FL-2, what is the vertical component of the leakage flux at the middle of the defect gap of a surface defect?a. zerob. maximumc. equal to horizontal componentd. divergente. convergentY.91

Figure FL-2


Vertical component of the leakage flux at the middle of the defect = 0

At maxima only horizontal component


9. In circular magnetization, the recommended magnetizing current in amperes per linear inch of section thickness is:a. 200 to 400 A/inb. 400 to 600 A/inc. 600 to 800 A/ind. 800 to 1000 A/ine. 1000 to 1200 A/inG.30.13

circular magnetization → circumferential magnetization?

10. Flux leakage techniques can normally examine for:a. surface flaws onlyb. subsurface defects onlyc. defects at any locationd. surface and near-surface defectsG.30.1


11. A relative motion between specimen and a ___ _ is needed in order to pick-up leakage flux.a. search coilb. hall probec. magneto probed. magneto resistore. piezoelectric crystal0.302

12. For a given crack with a given magnetic field, more magnetic lines of force are deflected out of the magnetic path when the:a. length of the crack is parallel to the magnetic lines of forceb. length of the crack is perpendicular to the magnetic lines of forcec. length of the crack is diagonal to the magnetic lines of forced. edges of the crack are polarizedG.30.3-4


13. The curve shown in Figure FL-3 is called a:a. hysteresis loopb. minor loopc. recoil curved. magnetization curvee. permeability curveG.33.3

Figure FL-3


14. A Hall effect probe measures:a. permeabilityb. conductivityc. tangential field strengthd. field strength perpendicular to the probe surfacee. reluctanceG.33.11

15. The ratio BIH is equivalent to a material's:a. field strengthb. reluctancec. permittivityd. permeabilitye. relative permeabilityG.33.15


PermittivityIn electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how much electric field (more correctly, flux) is 'generated' per unit charge in that medium. More electric flux exists in a medium with a low permittivity (per unit charge) because of polarization effects. Permittivity is directly related to electric susceptibility, which is a measure of how easily a dielectric polarizes in response to an electric field. Thus, permittivity relates to a material's ability to resist an electric field and "permit" is a misnomer.

https://en.wikipedia.org/wiki/Permittivity/


16. Which discontinuity in Figure FL-4 would show the strongest indication?a. Ab. Bc. Cd. DU.46

Figure FL-4(for FLT the detection principle is interference with the magnetic fields not the eddy current induced)


17 The optimum angle at which the magnetic field must intersect a discontinuity in a test specimen is:a. 90°b. 60°c. 45°d. 30°U.46

18. In the flux leakage examination of tubular products, which of the following discontinuities can be detected?a. longitudinally orientedb. transversely orientedc. sliversd. all of the aboveDD.627


19. In the flux leakage testing of tubular products, the amplitude of the signalreceived from a discontinuity will depend upon:a. the depth of the discontinuityb. the orientation of the discontinuityc. the distance between the flux leakage sensor and the tubed. all of the abovee. a and cDD.629

20. Flux leakage inspection can reveal the presence of:a. discontinuitiesb. voidsc. inclusionsd. either b or ce. a, b, and cC.l0-2


TWO

Level II Q&A-Flux Leakage Testing Method


Level II - Standard Answers1. D 2. d 3. c 4. b 5. a 6. c 7. b 8. d 9. a 10. d 11. a 12. c 13. a 14. d 15. b16. c 17. a 18. c 19. b 20. c 21. d 22. c 23. d 24. e


1. In flux leakage inspection of wire ropes using an encircling coil as a sensor,the response of the coil depends on what parameters of the wire break?a. cross-sectional area of broken wireb. location of broken wire within the cross-sectionc. gap between the ends of the broken wired. all of the aboveBB.144-46

2. The highest sensitivity of a Hall generator is obtained when the direction ofthe magnetic field in relation to the largest surface of the Hall probe is:a. parallelb. at an angle of 46°c. at an angle of 30° or 60°d. perpendiculare. none of the aboveG.33.11


3. The best flaw detection sensitivity is obtained when the magnetizing flux is:a. parallel to the flaw's longest dimensionb. perpendicular to the flaw's shortest dimensionc. perpendicular to the flaw's longest dimensiond. none of the aboveU.330

4. In flux leakage inspection for flaws, the part being inspected should be magnetized:a. beyond saturationb. to saturation or near saturationc. well below saturationd. using a combination of ac and de fieldsU.330


5. An advantage that flux leakage testing has in comparison with eddy currenttesting is that flux leakage testing is:a. less sensitive to interferences due to surface roughnessb. useful on products at temperatures above the Curie pointc. useful on austenitic steelsd. capable of much higher inspection ratesN.122-123


6. Using Figure FL-5, flux leakage strength decreases with distance (d) fromthe defect surface and is approximately proportional to:a. db. 1/dc. 1/d2

d. 1d3

e. 1/d4

Figure FL-5


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

d. A =kD3

e. A =kD4

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

Figure FL-6

W


8. What particular type of defect is not indicated by flux leakage techniques?a. overlapb. grain boundary crackc. slag inclusion with crackd. surface contaminatione. longitudinal seamAA.16

9. Electric current flowing in a magnet will alter the direction of magnetic fields in a magneta. trueb. falseG.30.30-34


Grain Boundary Crack


10. The strength of the magnetic field in the interior of a long solenoid isdetermined by:a. the number of turns in the solenoidb. the strength of applied currentc. the length of the solenoidd. all of the abovee. none of the above (for eddy current interior of exciting coil was assumed constant)0.307

11. In longitudinal magnetization by a coil, for most effective magnetization,the part to be magnetized should be:a. held against the inside wall of the coilb. positioned in the center of the coilc. held near the outside wall of the coild. held half way between the wall and center of the coilG.30.14


12. Due to the unique construction and great lengths of wire ropes, a practical and reliable NDT technique for testing is:a. acoustic emissionb. ultrasonicsc. magnetic techniquesd. radiatione. none of the aboveEE.62

13. In dc magnetic testing of steel wire ropes, one type of magnetizing method is preferred over the other for the following reasons:a. permanent magnet: constant magnetic field intensity, no magnetizing currentb. electromagnet: fluctuating magnetic field intensity, heavier, more rugged constructionc. electromagnet: constant magnetic field intensity, lighter-weight constructiond. permanent magnet: fluctuating magnetic field intensity, heavier, more rugged constructionFF.4


14. The number of broken wires at a particular location on a wire rope cannot always be determined because:a. the broken ends overlapb. a visual inspection for verification is impossible because the breaks are inside the ropec. the strip chart recorder speed was too slowd. the conditions stated above are all possibilitiese. the strip chart recorder speed was too fastCC.ll, 16, 18, 19

15. As a general rule, hard materials have:a. high coercive force and are easily demagnetizedb. high coercive force and are not easily demagnetizedc. low coercive force and are easily demagnetizedd. low coercive force and are not easily demagnetizede. none of the aboveG.30.22


16. The point (P) shown on the hysteresis loop in Figure FL-7 is called the:a. coercive forceb. initial permeabilityc. residual field (Remanence)d. leakage fluxe. demagnetization point

Figure FL-7


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

B ∝ D/W ?

D

W


18. A calibration standard is prepared using holes. With respect to thereference size, it is considered good practice to:a. include holes larger in diameter than the reference sizeb. include holes smaller in diameter than the reference sizec. include holes both larger and smaller in diameter than the reference sized. include holes of the reference size onlyDD.630

19. When testing tubes, if the sensor bounces along the surface this may:a. make it difficult to estimate fault severityb. cause false signalsc. decrease speed of inspectiond. distort the magnetizing systemDD.628


20. In flux leakage testing, the greatest tube wall thickness for whichmaximum sensitivity can be maintained in mm (in.) is:a. 0.08 mm (0.003 in.)b. 0.8 mm (0.03 in.)c. 8 mm (0.3 in.)d. 76 mm (3 in.)U.330

21. The following are used in determining magnetic flux leakage:a. coilb. magnetic tapec. Hall elementd. all of the abovee. a and b0.316-317


22. In the examination of tubular products, a circumferential (transverse)magnetic field can be established by:a. properly positioning north and south poles of a magnet with respect to the tubeb. using a central conductor positioned in the tubec. a and bd. neither a nor bDD.629


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


24. Calibration standards used in the flux leakage examination of tubularproducts should be carefully prepared since the flux leakage signal responsefrom the notch will be affected by:a. notch orientationb. notch widthc. notch lengthd. notch depthe. all of the aboveDD.630


Three

Level III Q&A-Flux Leakage Testing Method


Level III - Standard Answers1. B 2. d 3. d 4. a 5. c 6. b 7. c 8. b 9. b 10. c 11. a 12. c 13. e 14. a 15. 2. b 16. c 17. e 18. b 19. e 20. d 21. b


1. In flux leakage testing of wire rope, the system of two different diametersearch coils is frequently used. What is the main reason for using such asystem? (See Figure FL-8.)a. to compensate the influence of testing speedb. to find the radial location of wire breaksc. to detect corrosiond. to detect small cracks inside the ropee. to detect gradual decreasing of rope diameterGG.378

Figure FL-8


2. In flux leakage testing of wire rope, two separate outer broken wires willproduce two separate indications if there is sufficient distance between thebreaks. What is the maximum rope speed in feet per minute that wouldproduce two separate indications when the cutoff frequency of the recorder is60kHz and the breaks are 25 mm (1 in.) apart? (See Figure FL-9.)a. 60 fpmb. 120 fpmc. 240 fpmd. 300 fpm 300x12/60= 60 in/s, 60Hz will detect the indication?e. 360 fpm for 60kHz the speed = 300 x 103 fpm?GG.378

Figure FL-9


3. Which devices are used to detect flux leakage?a. coils, Hall probes, and transistorsb. piezoelectric crystals, Hall probes, and magnetic diodesc. piezoelectric crystals, transistors, and magnetic diodesd. coils, Hall probes, and magnetic diodesN.123


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

FL-10


5. In a properly operating flux leakage system, pipe defects occurring atincreased depths from the surface will generate signals with:a. increased phase differencesb. higher frequency characteristicsc. lower frequency characteristicsd. increased signal noise ratiosL.54

6. Lift-off reduces the amplitude of the flux leakage signal. The other significant effect it has on the signal is a:a. change in phase (?)b. change in frequencyc. change in signal noise ratiod. all of the aboveP.31A


3.9 COUPLINGIn eddy current testing, the test piece is coupled to the test coil by the coil’smagnetic field, which is quite similar to transformer action. Coupling efficiencyis intimately related to lift-off; coupling efficiency is 100% when lift-off is zero.Lift-off describes the change in electromagnetic coupling as a function ofprobe clearance. As lift-off or probe clearance increases from the test surface, coupling efficiency and eddy current probe output decreases.

Lift-off changes both the (1) amplitude and (2) phase of the eddy current signal.

Impedance changes produced by small lift-off variations are greatest when the coil is in contact with the test material. For this reason, spring-loaded probes and self comparison coil or differential coil arrangements are frequently used. With eddy current testing, lift-off is a complex variable that can be detected and compensated for through frequency selection to achieve a desirable operating point on the complex impedance plane

Introduction Nondestructive Testing-PAUL E. MIX


7. Eddy current shielding, the name given to the unidirectional eddy current flow in products inspected by the flux leakage method, is caused by: a. the interaction between the test magnetic field and a residual field in the product b. fluctuations in the de magnetizing currentc. rapidly occurring flux changes in the product created by the rotation of the magnetic fieldd. rapidly occurring impedance changes in the pickup coilsAA.16

12. Too high a rotational test speed or too high active pole rotating headspeed can cause the loss of an indication from an ID defect. What can this beattributed to?a. excessive generated surface noiseb. limitations of the flux sensor elementsc. eddy current shieldingd. reverse magnetization effecte. none of the aboveAA.16


8. A flux leakage pipe inspection system with two inspection heads, eachhaving 152 mm (6 in.) long scan paths and rotating at 180 rpm on a 178 mm(7 in.) diameter tube, can have a maximum throughput speed of ______per minute for 100% inspection coverage.a. 201 m (660ft)b. 55 m (180ft)c. 49 m (162ft)d. 27 m (90 ft)e. 25 m (81 ft)U.330,338

180rpm x 6” = 1080 in/min, 2 head thus coverage = (1080 x2)/12 ft/min = 180’/min.

6 in. 7 in.


9. A flux leakage pipe inspection system with two inspection heads, each having 152 mm (6 in.) long inspection areas and rotating at 180 rpm on a 178 mm (7 in.) diameter pipe, would require a throughput speed of _____per minute to provide a 110% inspection coverage.a. 60 m (198ft)b. 49 m (162ft)c. 45 m (146ft)d. 25 m (81 ft)e. 22 m (73 ft)P.22A

10. The tubular product parameter having the greatest influence on the flux density of the magnetic field in the part (assuming the magnetizing force (H) and the material's permeability μ remains constant) is the: a. chemistry of the product b. diameter of the productc. wall thickness of the productd. length of the productU.330


11. A defect having an inclined angle to the surface has a flux leakage that is (see Figure FL-11):a. lower than a similar normal defect (B∙cos θ?)b. equal to a similar normal defectc. higher than a similar normal defectd. all of the aboveY.91

Figure FL-11


12. Too high a rotational test speed or too high active pole rotating headspeed can cause the loss of an indication from an ID defect. What can this beattributed to?a. excessive generated surface noiseb. limitations of the flux sensor elementsc. eddy current shieldingd. reverse magnetization effecte. none of the aboveAA.16


13. A current carrying conductor is surrounded by a tube (see Figure FL-12). Magnetic fields exist in the tube, if the tube is made of:a. steelb. copperc. aluminumd. leade. all of the aboveG.30.6

Figure FL-12


14. A tube is magnetized by passing a uniform current through the tube.There are inside and outside defects in the tube (see Figure FL-13). The twodefects have the same dimension and geometry. The defect signal strength:a. is stronger for the outside defect than for the inside flawb. is stronger for the inside defect than for the outside flawc. is the same for both defectsd. is an uncertaintye. depends on the permeability of the tubeG.30.6


14. A tube is magnetized by passing a uniform current through the tube. There are inside and outside defects in the tube (see Figure FL-13). The two defects have the same dimension and geometry. The defect signalstrength:a. is stronger for the outside defect than for the inside flawb. is stronger for the inside defect than for the outside flawc. is the same for both defectsd. is an uncertaintye. depends on the permeability of the tubeG.30.6

B= 0 at internal space

https://www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/CircularFields.htm


Circular Magnetic Fields Distribution and Intensity

https://www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/CircularFields.htm


15. A discontinuity in a steel wire rope may be detected with a dc magneticinstrument if:

a. the rope is magnetized to saturation, the discontinuity is polarized, thespeed of the rope is great enough to induce a detectable voltage acrossthe discontinuity

b. the area surrounding the discontinuity is magnetized to saturation, the discontinuity is polarized, the speed of the rope is great enough to induce a detectable voltage across the discontinuity

c. the rope is magnetized to saturation, the speed of the rope is great enough to induce a detectable voltage across the discontinuity

d. the rope is magnetized to saturation, the discontinuity is polarizedCC.10


MFL of Wire Rope Principle the area surrounding the discontinuity is magnetized to saturation, the discontinuity is polarized, the speed of the rope is great enough to induce a detectable voltage

across the discontinuity

MFL of Wire Rope Principle


16. What is the SI unit for magnetic flux density B ?a. Weber ( magnetic flux, Ф)b. Gauss (B in CGS)c. Tesla (B in SI) (1 teslas = 10000 Gauss) http://www.magnii.com/magnetic-units-converter.html

d. none of the abovee. all of the aboveW.71

B is measured in teslas (symbol:T) and newtons per meter per ampere (symbol: N·m−1·A−1 or N/(m·A)) in the SI. https://en.wikipedia.org/wiki/Magnetic_field

17. What is the SI unit for magnetic field strength?a. Weberb. Teslac. Ampered. Henrye. Ampere per meterW.71


A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where

H is measured in units of amperes per meter (symbol: A·m-1 or A/m) in the SI.

B is measured in teslas (symbol:T) and newtons per meter per ampere [symbol: N·m-1·A-1 or N/(m·A)] in the SI. (1 teslas = 10000 Gauss)

B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges. Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic tensor; the split of this tensor into electric and magnetic fields depends on the relative velocity of the observer and charge. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons.

https://en.wikipedia.org/wiki/Magnetic_field


Weber (Magnetic Flux Ф)In physics, specifically electromagnetism, the magnetic flux (often denoted Φor ΦB) through a surface is the surface integral of the normal component of the magnetic field B passing through that surface.

The SI unit of magnetic flux is the weber (Wb) (in derived units: volt-seconds), and the CGS unit is the maxwell.

Magnetic flux is usually measured with a fluxmeter, which contains measuring coils and electronics, that evaluates the change of voltage in the measuring coils to calculate the magnetic flux.

https://en.wikipedia.org/wiki/Magnetic_flux


Gauss (Magnetic Flux Density)gauss, unit of magnetic induction in the centimetre-gram-second CGS system of physical units. One gauss corresponds to the magnetic flux density that will induce an electromotive force of one abvolt (10-8 volt) in each linear centimetre of a wire moving laterally at one centimetre per second at right angles to a magnetic flux. One gauss corresponds to 10-4 tesla (T), the International System Unit. The gauss is equal to 1 maxwell per square centimetre, or 10-4 weber per square metre. Magnets are rated in gauss. The gauss was named for the German scientist Carl Friedrich Gauss.

http://global.britannica.com/science/gauss


Electrical Inductance - HenryThe henry (symbol H) is the unit of electrical inductance in the International System of Units.The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England. The magnetic permeability of a vacuum μo is 4π×10-7 H m-1 (henries per metre).

The National Institute of Standards and Technology provides guidance for American users of SI to write the plural as "henries". The inductance of an electric circuit is one henry when an electric current that is changing at one ampere per second results in an electromotive force across the inductor of one volt:

v(t) = L di/dt

where v(t) denotes the resulting voltage across the circuit, i(t) is the current through the circuit, and L is the inductance of the circuit.

https://en.wikipedia.org/wiki/Henry_(unit)


Magnetic Permeability (B/H)In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. Hence, it is the degree of magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter μ. The term was coined in September 1885 by Oliver Heaviside. The reciprocal of magnetic permeability is magnetic reluctivity.

In SI units, permeability is measured in henries per meter (H·m-1), or newtons per ampere squared (N·A-2). The permeability constant (μ0), also known as the magnetic constant or the permeability of free space, is a measure of the amount of resistance encountered when forming a magnetic field in a classical vacuum. The magnetic constant has the exact (defined) value µ0 = 4π×10-7 H·m-1≈ 1.2566370614…×10−6 H·m-1 or N·A-2).

A closely related property of materials is magnetic susceptibility, which is a dimensionless proportionality factor that indicates the degree of magnetization of a material in response to an applied magnetic field.

https://en.wikipedia.org/wiki/Permeability_(electromagnetism)


18. What is the SI unit for magnetic permeability?a. Ampere per meterb. Henry per meterc. Henryd. Gauss per metere. Tesla

μ = B/H


19. A ferromagnetic part can be demagnetized by:a. raising its temperature above the curie pointb. withdrawing the part from an ac coilc. alternately reversing and reducing the applied fieldd. none of the abovee. all of the aboveG.30.22-23


More Reading: Magnetic Flux & Gauss lawhttp://info.ee.surrey.ac.uk/Teaching/Courses/EFT/dynamics/html/magnetic_flux.html


20. Figure FL-14 shows an arrangement of probe-coils in a Forester probe used for measuring:a. the static field componentb. the normal component of the tangential fieldc. the tangential component of the normal fieldd. the field gradiente. all of the aboveG.33.1

Figure FL-14


21. In flux leakage testing the maximum permissible speed of probe or tube movement with respect to the other is:a. 914 m/min (3 000 ft/min)b. 91 m/min (300 ft/min)c. 9 m/min (30 ft/min)d. 0.9 m/min (3 ft/min)U.338


making


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

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