NDT Discontinuity Interpretation and Evaluation 2 — Questions and Answers
Question 1: A weld radiograph shows a dark, elongated indication with fuzzy edges running parallel to the weld axis. This is most likely:
- Slag inclusion
- Incomplete fusion (Correct answer)
- Porosity cluster
- Tungsten inclusion
Correct answer: Incomplete fusion
Incomplete fusion appears as an elongated dark line with fuzzy or diffuse edges parallel to the weld joint.
Question 2: In ultrasonic testing, a discontinuity signal that appears at half the material thickness and disappears when the probe is angled slightly is most characteristic of:
- Porosity
- Lamination (Correct answer)
- Lack of penetration
- Transverse crack
Correct answer: Lamination
Laminations are planar discontinuities parallel to the plate surface that produce signals at mid-thickness and are highly angle-sensitive.
Question 3: During magnetic particle testing, a tight linear indication is found perpendicular to the applied field. The inspector should:
- Accept it as a surface scratch
- Re-inspect with field perpendicular to the indication (Correct answer)
- Reject the part immediately without further testing
- Apply a stronger magnetizing current only
Correct answer: Re-inspect with field perpendicular to the indication
An indication perpendicular to the field may be a false indication; rotating the field 90° confirms whether it is a true discontinuity.
Question 4: A liquid penetrant indication that bleeds out rapidly and becomes large and diffuse most likely indicates:
- A tight fatigue crack
- A shallow scratch
- A subsurface void
- A gross surface porosity or large opening (Correct answer)
Correct answer: A gross surface porosity or large opening
Rapid, diffuse bleed-out is characteristic of wide, open discontinuities such as gross porosity that hold large volumes of penetrant.
Question 5: When evaluating a radiograph, a bright (white) round spot surrounded by a dark halo is most likely:
- Gas porosity
- Tungsten inclusion (Correct answer)
- Slag inclusion
- Undercut
Correct answer: Tungsten inclusion
Tungsten inclusions appear as bright white dense spots because tungsten is more radiographically opaque than the surrounding weld metal.
Question 6: A phased array ultrasonic S-scan image shows a curved, bright indication originating from the weld root. The most probable discontinuity is:
- Centerline crack
- Lack of root penetration (Correct answer)
- Root concavity
- Slag at root
Correct answer: Lack of root penetration
Lack of root penetration produces a strong reflector at the root region visible on S-scan as a bright indication at the expected root depth.
Question 7: In eddy current testing, a discontinuity signal whose phase angle is near 0° on the impedance plane most likely indicates:
- A deep subsurface void
- A surface crack
- Conductivity variation
- Lift-off change (Correct answer)
Correct answer: Lift-off change
Lift-off signals appear near 0° phase on the impedance plane, which is why lift-off direction is established first to separate it from defect signals.
NDT Discontinuity Interpretation and Evaluation 2
A weld radiograph shows a dark, elongated indication with fuzzy edges running parallel to the weld axis.
This is most likely: