Electromagnetic Testing

Question 1

Eddy currents are circulating electrical currents induced in conductive materials by:

A. continuous direct current.

B. gamma rays.

C. an alternating magnetic field.

D. a piezoelectric force.

Answer 1

1) - C

Question 2

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. transformer.

B. capacitor.

C. storage battery.

D. generator.

Answer 2

2) - A

Question 3

ET relies on the principle of:

A. magnetostriction.

B. electromagnetic induction.

C. piezoelectric energy conversion.

D. magnetomotive force.

Answer 3

3) - B

Question 4

What happens when the electrical current in an eddy current coil reverses direction?

A. The direction of the eddy currents in the test part remains the same.

B. The eddy currents in the test part will change phase by 45°.

C. The direction of the eddy currents in the test part also reverses.

D. The eddy currents in the test part will change phase by 90°.

Answer 4

4) - C

Question 5

In order to generate measurable eddy currents in a test specimen, the specimen must be:

A. an electrical conductor.

B. an electrical insulator.

C. a ferromagnetic material.

D. a nonmagnetic material.

Answer 5

5) - A

Question 6

The magnetic field generated by eddy currents induced in a test specimen:

A. reinforces the magnetic field that induced the eddy currents.

B. cancels the magnetic field that induced the eddy currents.

C. opposes the magnetic field that induced the eddy currents.

D. has no effect on the magnetic field that induced the eddy currents.

Answer 6

6) - C

Question 7

In ET, what is IACS a recognized abbreviation for?

A. Induced Alternating Current System

B. Inductively Activated Comparison System

C. Internal Applied Current System

D. International Annealed Copper Standard

Answer 7

7) - D

Question 8

In ET, what is the specimen coupled to the test coil by?

A. Core coupling

B. Magnetic saturation

C. The coil’s electromagnetic fields

D. Magnetic domains

Answer 8

8) - C

Question 9

When is the penetration of eddy currents in a conductive material decreased?

A. When the test frequency or conductivity of the specimen is decreased.

B. When the test frequency is decreased or conductivity of the specimen is increased.

C. When the test frequency, conductivity of the specimen, or permeability of the specimen is increased.

D. When the permeability of the specimen is decreased.

Answer 9

9) - C

Question 10

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)

Answer 10

10) - D

Question 11

A term used to describe the effect observed due to a change in the coupling between a test specimen and a flat probe coil when the distance of separation between them is varied is:

A. liftoff.

B. fill factor.

C. edge effect.

D. end effect.

Answer 11

11) - A

Question 12

When performing eddy current testing, under what condition are discontinuities most easily detected?

A. When the eddy currents are coplanar with the major dimension of the discontinuity.

B. When the eddy currents are perpendicular to the major plane of the discontinuity.

C. When the eddy currents are parallel to the major dimension of the discontinuity.

D. When the eddy currents are 90° out of phase with the current in the coil.

Answer 12

12) - A

Question 13

Which of the following discontinuities is easiest to detect with an electromagnetic test?

A. A subsurface crack which lies parallel to the direction of the eddy current.

B. A discontinuity located in the center of a 51 mm (2 in.) diameter bar.

C. A radial crack that extends to the outer surface of a 51 mm (2 in.) diameter bar.

D. A subsurface radial crack located at a depth of 13 mm (0.5 in.) in a 51 mm (2 in.) diameter bar.

Answer 13

13) - C

Question 14

What is a term used to define the timing relationships involved in alternating current signals?

A. Magnitude

B. Phase

C. Impedance

D. Time-gain correction

Answer 14

14) - B

Question 15

The impedance of a test coil can be represented by the vector sum of:

A. inductive reactance and resistance.

B. capacitive reactance and resistance.

C. inductive reactance and capacitive reactance.

D. inductive reactance, capacitive reactance, and resistance.

Answer 15

15) - A

Question 16

What does the term “fill factor” apply to?

A. A surface coil

B. Coaxial cable

C. An encircling coil

D. The ability to null an eddy current instrument

Answer 16

16) - C

Question 17

Which of the following materials would be more likely used as a mounting material for a probe coil?

A. Aluminum

B. Plastic

C. Copper

D. Nonferromagnetic steel

Answer 17

17) - B

Question 18

Which heat exchanger tube material CANNOT be inspected by standard eddy techniques using an internal coil probe?

A. Copper

B. Austenitic stainless steel

C. Brass

D. Carbon steel

Answer 18

18) - D

Question 19

Reference standards used for ET:

A. must contain artificial discontinuities such as notches and drilled holes.

B. must contain natural discontinuities such as cracks and inclusions.

C. must be free of measurable discontinuities, but may contain artificial or natural discontinuities, or may be free of discontinuities, depending on the test system and the type of test being conducted.

D. must be constructed from the same material of the object being inspected.

Answer 19

19) - C

Question 20

Which of the following conditions would be the most difficult to detect when testing a rod using an encircling coil?

A. A short surface crack that has a depth of 10% of the rod diameter.

B. A small inclusion in the center of the rod.

C. A 5% change in diameter.

D. A 10% change in conductivity.

Answer 20

20) - B

Question 21

The thickness of nonconductive coatings on a conductive base can be most simply measured by:

A. observing the liftoff effect caused by the coating.

B. testing both sides of the specimen.

C. varying the test frequency over a given range during the test.

D. using a specially shaped encircling coil.

Answer 21

21) - A

Question 22

Some of the products commonly tested using encircling coils are:

A. rods, tubes, and wire.

B. interior of hollow tubes.

C. sheets and metal foil.

D. square billets and plates.

Answer 22

22) - A

Question 23

It is often possible to sort various alloys of a nonmagnetic metal using ET when:

A. there is a unique range of permeability values for each alloy.

B. there is a unique range of conductivity values for each alloy.

C. the direction of induced eddy currents varies for each alloy.

D. the magnetic domains for each alloy are different.

Answer 23

23) - B

Question 24

When conducting ET on tubing with a system that includes a frequency discriminating circuit, which of the following variables would be classified as a high-frequency variable?

A. Conductivity changes

B. Diameter changes

C. Wall thickness variations

D. Small discontinuities

Answer 24

24) - D

Question 25

Tubing is generally inspected using: A. U-shaped coils. B. gap coils. C. encircling coils. D. a sliding probe.

Answer 25

25) - C

Question 26

An out-of-phase condition between current and voltage: A. can exist in both the primary and secondary windings of an eddy current coil. B. can exist only in the secondary winding of an eddy current coil. C. can exist only in the primary winding of an eddy current coil. D. exists only in the test specimen.

Answer 26

26) - A

Question 27

For age hardenable aluminum and titanium alloys, changes in hardness are indicated by changes in: A. retentivity. B. permeability. C. conductivity. D. magnetostriction.

Answer 27

27) - C

Question 28

In performing inspection of heat exchanger tubing using an internal differential probe, which type of defect would be difficult to detect? A. Longitudinally oriented crack B. Localized corrosion pit C. Circumferentially oriented crack D. Dent

Answer 28

28) - C