NDT Eddy Current Testing Theory 3

Question 1

Which of the following materials has the HIGHEST electrical conductivity, making eddy current testing most effective at low frequencies?

Accepted Answer

Copper

Answer

Copper has electrical conductivity of approximately 58 MS/m, far higher than titanium, stainless steel, or carbon steel, allowing eddy currents to flow very freely.

Question 2

What is 'phase analysis' used for in eddy current testing?

Accepted Answer

Distinguishing between different types of discontinuities and their depth

Answer

Phase analysis uses the phase angle of the eddy current signal to discriminate between defect types (surface vs. subsurface) and estimate their depth.

Question 3

An eddy current technician notices the signal drifts continuously during scanning of a large aluminum plate. The MOST likely cause is:

Accepted Answer

Thermal drift changing probe impedance as temperature varies

Answer

Thermal drift occurs when probe or material temperature changes during scanning, causing a gradual impedance shift unrelated to defects.

Question 4

In the context of eddy current testing, what does 'fill factor' describe for encircling coil probes?

Accepted Answer

The ratio of the test piece cross-sectional area to the coil's inside area

Answer

Fill factor (η) is the ratio of the test piece's cross-sectional area to the coil's inner cross-sectional area, and a higher fill factor improves coupling and sensitivity.

Question 5

When testing nonconductive coatings over a conductive substrate, the eddy current technique can measure coating thickness because:

Accepted Answer

Coating thickness changes the effective lift-off distance from the conductor

Answer

A nonconductive coating acts as a spacer, increasing the effective lift-off between the probe and the conductive base material, which is directly related to coating thickness.

NDT - Non-Destructive Testing Practice Test

NDT - Non-Destructive Testing Practice Test

NDT Eddy Current Testing Theory 3