NEW SOUTH WALES DEPARTMENT OF EDUCATION AND TRAINING Manufacturing and Engineering ESD. Sample Examination EA605

Transcription

1 Name: NEW SOUTH WALES DEPARTMENT OF EDUCATION AND TRAINING Manufacturing and Engineering ESD Sample Examination EA605 EDDY CURRENT TESTING AS3998 LEVEL 2 GENERAL EXAMINATION 6161C * * * * * * * Time allowed Two hours plus 10 minutes reading time PART A ATTEMPT ALL QUESTIONS PART B ATTEMPT ALL QUESTIONS PART A 2 marks per question PARTB 4 marks per question TOTAL MARKS AVAILABLE = 110 PART A ALL QUESTIONS TO BE ANSWERED ON THE EXAMINATION PAPER PART B ALL QUESTIONS TO BE ANSWERED ON THE EXAMINATION PAPER Non-programmable calculators may be used.

2 SECTION A Answer ALL questions by placing the letter representing your answer in the space provided. There is only ONE correct answer to each question. Each question 2 marks 1. One method for reducing indications caused by gradual dimensional changes and finding indications caused by discontinuities is to: A) include a high-pass filter in the eddy current test equipment B) include a low-pass filter in the eddy current test equipment C) increase the band pass of the amplifier D) use the impedance method of testing. 2. To decrease the effect on conductivity readings due to variations in test part thickness when testing: A) the test frequency should be increased B) the test frequency should be decreased C) the fill-factor should be decreased D) there is no practical method for decreasing this effect. 3. Discontinuities will be most easily detected when the eddy currents are: A) coplanar with the major dimension of the discontinuity B) perpendicular to the major dimension of the discontinuity C) parallel to the major dimension of the discontinuity D) 90 degrees out of phase with the current in the coil 4. 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-factor B) edge effect C) end effect D) lift-off

3 5. A term used to define the phenomenon where, at very high frequencies, the eddy current flow is restricted to en extremely thin outer later of the conductor is: A) skin effect B) high-frequency filtration C) low-frequency filtration D) any one of the above 6. Which of the following could be used to suppress unwanted highfrequency harmonics? A) a low-pass filter B) an oscillator C) a phase discriminator D) a high-pass filter 7. The impedance change of an eddy current test coil due to a change in test part characteristics can be most easily analysed as a combined change in: A) capacitive reactance and resistance B) harmonic frequencies and inductive reactance C) signal amplitude and phase D) retentivity and harmonic frequencies 8. The inductive reactance can be calculated using the formula: A) X L = 2 π L B) X L = 1/2 π L C) X L = 2 π f L D) X L = 1 R 9. When conducting an eddy current test, variations in output signal can be caused by variations in: A) test speed B) impedance of a pickup coil C) magnetic reaction field D) all of the above

4 10. 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) differential probe B) absolute probes C) bobbin probes D) double wound 11. In a test coil consisting of both a primary and secondary winding, the voltage across the secondary is a function of: A) test material permeability B) test frequency C) geometry of the test object D) all of the above 12. Eddy current testing relies on the principle of: A) magnetostriction B) electromagnetic induction C) piezoelectric energy conversion D) magnetomotive force 13. Magnetic saturation of a ferromagnetic test sample is best done with: A) a.c. fields B) d.c. fields C) either of the above D) neither A or B 14. The three major specimen parameters which influence eddy current testing are: A) electrical conductivity, frequency, and material geometry B) density, permeability, and frequency C) electrical conductivity, permeability, and material geometry D) thermal conductivity, electrical conductivity, and permeability

5 15. Doubling the number of turns on a coil will: A) double the inductance B) halve the inductance C) decrease the inductance by a factor of four D) increase the inductance by a factor of four 16. 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 phase B) The phase of the OD discontinuity leads the phase of the ID discontinuity C) The phase of the OD discontinuity lags the phase of the ID discontinuity D) indeterminent 17. A term used to define an instrumentation technique which discriminates between variables in the test part by the different phase angle changes which these conditions produced in the test signal is: A) phase distortion B) phase shifting C) phase discrimination D) phase analysis 18. 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 Hz B) 1.25 khz C) 12.5 Hz D) 12.5 khz 19. At a fixed test frequency in which of the following materials will the eddy current penetration be greatest? A) aluminium (57 % IACS conductivity) B) brass (15% IACS conductivity) C) copper (95% IACS conductivity) D) stainless steal (4% IACS conductivity)

6 20. If the test frequency increases while the field strength is held constant, the surface eddy current density: A) decreases B) increases C) remain the same D) could do any of the above 21. As the fill-factor decreases, the impedance variation of a pickup coil produced by a given change in conductivity will: A) increase B) remain the same C) decrease D) could do any of the above 22. In Figure 1, a change in the f/fg ratio will result in: A) a change in only the magnitude of the voltage across the coil B) a change in only the phase of the voltage across the coil C) a change in both the phase and magnitude of the voltage across the coil D) no change in the phase or magnitude of the voltage across the coil FIGURE 1

7 23. In Figure 2, the solid curves are plots for different values of: A) heat treat B) conductivity C) fill-factor D) permeability FIGURE 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 diameter B) gradual changes in conductivity C) changes in temperature D) short flaws 25. The magnetic domains in an unmagnetised ferromagnetic material are: A) arranged to facilitate the conduction of electrons B) randomly oriented and neutralise each other C) uniformly oriented D) create a major north and south pole in the material

8 26. When a magnetic material is placed in a region of an applied magnetising force (H), magnetic field (B) is developed in the material by means of: A) induction B) conduction C) heat transfer D) magnetic domain transfer 27. With all ferrous materials, an increase in carbon content: A) reduces the resistivity of the material B) increases the saturation flux density of the material C) decreases the permeability of the material D) decreases the retentivity of the material 28. To eliminate any dependence upon the number of turn of a test coil, the inductance values of an impedance diagram are: A) disregarded B) normalised C) corrected to a value of 1 D) none of the above 29. When testing a rod by eddy current method, the best sensitivity will be attained when the: A) fill-factor is as low as possible B) fill-factor is 0.5 C) fill-factor is as high as possible D) coil is made as large as possible 30. The use of magnetic shielding around the exciting coil will generally: A) increase the magnetic field extension but decrease the eddy current penetration B) increase the magnetic field extension and eddy current penetration C) decrease the magnetic field extension but increase the eddy current penetration D) decrease the magnetic field extension and eddy current penetration.

9 31. The formula used to calculate the impedance of an eddy current test coil is: A) Z = 2πfL B) Z = X L + R C) Z = X L + R D) Z 2 2 X L + R 32. A term used to define a standard used to ensure that the amplitude and phase characteristics of an eddy current test system do not drift during continuous testing is: A) calibration reference B) reference block C) performance reference D) penetrameter 33. Which of the following coil arrangements would eliminate or decrease the effects of minor variations in diameter, chemical composition, hardness, etc., which occur gradually along the length of a wire? A) external reference differential B) self-comparison differential C) single coil absolute D) double coil absolute 34. If the conductivity of a test par in an eddy current test coil decreases, the magnitude of the eddy currents at a given depth in the test specimen: A) increases B) remains the same C) decreases D) may increase or decrease 35. When the voltage applied to a circuit and the current through the circuit both reach their maximums and minimums at the same time, the voltage and current are: A) additive B) in phase C) regenerative D) out of phase.

10 Answer ALL questions in the space provided. SECTION B MARKS QUESTION 36 4 Determine a suitable probe frequency to achieve a standard depth of penetration of 5 mm when testing type 304SS having a conductivity of 4% IACS. QUESTION 37 4 A sample of aluminium bronze tubing 3.0 mm way thickness and conductivity 12% IACS is to be tested for cracks using an internal coil. What frequency would give a 90 separation between near-side (internal) and far-side (external) indications?

11 QUESTION 38 4 A probe with coil diameter 5 mm is to be used to measure the conductivity of an aluminium alloy. The conductivity is expected to be approximately 20% IACS and nil lift-off. Which the assistance of Figure 1, determine the optimum frequency at which measurement should be carried out. FIGURE 1

12 QUESTION 39 4 Give two advantages of Eddy Current (ET) inspection when compared with Liquid Penetrant (PT) inspection and one advantage of Liquid Penetrant inspection when compared with Eddy Current inspection. QUESTION 40 Define the terms and list the units and symbols for the following: 2 (a) Impedance 2 (b) Capacitive Reactance

13 QUESTION 41 4 State two (2) advantages of a differential probe over an absolute probe and a test requirement which makes use of one of these advantages. QUESTION 42 Magnetic field spread can create problems when performing an eddy current inspection. 1 (a) What is it? 1 (b) Is it more pronounced at high or low frequencies? 2 (c) What method is used to contain the field?

14 QUESTION 43 4 Sketch the normalised hysteresis curves for a ferromagnetic material, including the virgin curve, label the axes and all relevant features. QUESTION 44 4 Sketch the difference in the impedance plane display you would expect if you detected a surface defect with: (a) an absolute surface probe and (b) a differential surface probe. Briefly explain the reason for the difference in the displays.

15 QUESTION 45 Eddy current is used to measure the conductivity of aluminium alloys. This measurement assists in establishing the temper condition of aluminium alloy material. 2 (a) Name the units normally used by NDT personnel to measure conducitivity. 2 (b) Overaging results in a change in conductivity, is it an increase or a decrease? END OF EXAMINATION