NDT Discontinuity Interpretation and Evaluation 3 — Questions and Answers
Question 1: An ASME code requires that any linear indication greater than 3/16 inch in a weld be rejected. A PT indication measures 3/16 inch exactly. The correct disposition is:
- Reject — it equals the maximum allowable
- Accept — it does not exceed the limit (Correct answer)
- Grind and re-inspect before deciding
- Reject only if it is surface-breaking
Correct answer: Accept — it does not exceed the limit
The code specifies 'greater than' 3/16 inch, so an indication exactly at 3/16 inch is acceptable under that criterion.
Question 2: During UT inspection, multiple small signals appear scattered throughout the weld volume with low amplitude. The most likely cause is:
- Centerline hot crack
- Distributed porosity (Correct answer)
- Lack of sidewall fusion
- Undercut
Correct answer: Distributed porosity
Scattered low-amplitude signals throughout the volume are characteristic of distributed porosity, where each pore produces a small reflection.
Question 3: A radiographic image shows a dark, irregular line with a herringbone or chevron pattern along the weld centerline. This pattern is associated with:
- Solidification (hot) cracking (Correct answer)
- Hydrogen-induced cracking
- Lamellar tearing
- Overlap
Correct answer: Solidification (hot) cracking
Solidification cracks form along weld centerlines during cooling and often display a jagged or herringbone pattern following dendritic grain boundaries.
Question 4: In magnetic particle testing, a broad fuzzy linear indication is observed. Compared to a sharp, crisp indication, this suggests the discontinuity is:
- Closer to the surface
- Deeper below the surface (Correct answer)
- Wider at the opening
- Caused by a higher magnetizing current
Correct answer: Deeper below the surface
Subsurface discontinuities cause broader, less defined magnetic particle indications because the leakage flux spreads as it reaches the surface.
Question 5: An eddy current scan of a heat exchanger tube shows a signal whose depth reading is 80% through-wall. Per most fitness-for-service criteria, this tube should be:
- Monitored only
- Plugged or repaired immediately (Correct answer)
- Re-tested in six months
- Accepted if below 100%
Correct answer: Plugged or repaired immediately
Most industry standards (ASME, TEMA) require plugging or repair of heat exchanger tubes when wall loss reaches or exceeds 40–80% depending on code; 80% typically requires immediate action.
Question 6: A surface-breaking crack detected by PT is evaluated and found to be relevant. The next required step per most codes is:
- Report and monitor for growth
- Assess against the applicable acceptance criteria (Correct answer)
- Perform UT to determine depth before deciding
- Apply corrosion inhibitor and close the file
Correct answer: Assess against the applicable acceptance criteria
Once a relevant indication is identified, it must be compared against the applicable code acceptance criteria to determine accept or reject disposition.
Question 7: During radiographic interpretation, the film shows an area of uniform density lighter than the surrounding base metal. This most likely represents:
- Porosity cluster
- Thicker section or added material (Correct answer)
- Undercut
- Internal crack
Correct answer: Thicker section or added material
Lighter (less dense) areas on a radiograph indicate greater material thickness or higher density, which absorbs more radiation.
NDT Discontinuity Interpretation and Evaluation 3
An ASME code requires that any linear indication greater than 3/16 inch in a weld be rejected.
A PT indication measures 3/16 inch exactly.
The correct disposition is: