NDT Eddy Current Testing Theory 5

Question 1

What is the primary purpose of a reference standard (calibration standard) in eddy current testing?

Accepted Answer

To establish known signal responses for instrument setup and defect sizing

Answer

Reference standards contain artificial or natural discontinuities of known size that allow the technician to calibrate instrument settings and correlate signal amplitudes/phases to defect sizes.

Question 2

In eddy current testing, 'noise' most commonly refers to:

Accepted Answer

Unwanted signals from material variations, geometry, or probe wobble that mask defect indications

Answer

Noise in ECT is any unwanted signal — from surface roughness, microstructural variation, or probe instability — that reduces the signal-to-noise ratio and makes defect detection harder.

Question 3

An eddy current signal from a through-wall hole in a tube will appear on the impedance plane with:

Accepted Answer

Large amplitude and a phase angle that places it well below the lift-off line

Answer

A through-wall hole represents 100% wall loss and produces the largest signal with a phase angle characteristic of very deep or complete penetration, distinct from surface indications.

Question 4

When testing for cracks parallel to the coil winding direction in an encircling coil, what happens to sensitivity?

Accepted Answer

Sensitivity is minimized because cracks parallel to eddy current flow cause little disruption

Answer

Eddy currents flow circumferentially in a cylindrical test piece under an encircling coil, so longitudinal cracks running parallel to that flow cause minimal disruption and very weak signals.

Question 5

The 'operating point' on an impedance plane diagram is determined by:

Accepted Answer

The coil impedance when placed on a defect-free section of the test material at the selected frequency

Answer

The operating point is where the coil's normalized impedance falls on the impedance plane when coupled to a sound (defect-free) test specimen at the chosen test frequency.

NDT - Non-Destructive Testing Practice Test

NDT - Non-Destructive Testing Practice Test

NDT Eddy Current Testing Theory 5