NDT Ultrasonic Testing Principles 5

Question 1

What is the significance of the second critical angle in ultrasonic testing?

Accepted Answer

The incident angle beyond which total internal reflection occurs and no energy enters the second medium

Answer

The second critical angle is where the refracted shear wave reaches 90° and travels along the interface; beyond this angle, total internal reflection occurs and no bulk waves enter the material — only surface waves.

Question 2

What is 'dead zone' in pulse-echo ultrasonic testing?

Accepted Answer

The zone immediately below the test surface where defects cannot be detected due to ring-down of the initial pulse

Answer

The dead zone is the region directly beneath the transducer face where the transmitted pulse has not yet fully decayed, masking any echoes from near-surface defects during that period.

Question 3

Mode conversion during ultrasonic testing refers to:

Accepted Answer

The transformation of one wave type (e.g., longitudinal) into another (e.g., shear) at an interface or boundary

Answer

Mode conversion occurs when an ultrasonic wave strikes an interface at an angle, causing some energy to be transmitted or reflected as a different wave type (e.g., longitudinal converting to shear).

Question 4

Which display format provides the most complete volumetric representation of ultrasonic inspection data?

Accepted Answer

C-scan (plan view amplitude map of the inspected area)

Answer

The C-scan presents a top-view map showing amplitude or depth data across the entire inspected area, giving the most complete spatial picture of flaw distribution and coverage.

Question 5

In weld inspection using angle-beam UT, the 'skip distance' refers to:

Accepted Answer

The surface distance from the probe to the point where the beam reflects off the back wall and returns to the surface

Answer

The skip distance is the surface projection of the full beam path from probe exit point to the back-wall reflection point and back up to the scanning surface, equal to twice the half-skip distance.

NDT - Non-Destructive Testing Practice Test

NDT - Non-Destructive Testing Practice Test

NDT Ultrasonic Testing Principles 5