API 510 Inspection Methods & Nondestructive Testing 3 — Questions and Answers
Question 1: During phased array ultrasonic testing (PAUT) of a pressure vessel weld, what does the S-scan (sectorial scan) display show?
- A cross-sectional view of the weld using multiple beam angles from a single probe position (Correct answer)
- A plan view of the weld surface showing defect locations
- A linear scan along the weld length at a fixed angle
- The amplitude vs. time response from a single element
Correct answer: A cross-sectional view of the weld using multiple beam angles from a single probe position
The S-scan (sectorial scan) sweeps through multiple angles electronically, displaying a fan-shaped cross-section of the weld in a single probe placement.
Question 2: When performing external visual inspection of a pressure vessel, an inspector observes blistering of the paint coating near a weld. What should this observation prompt?
- Further NDE such as UT or MT to evaluate for possible cracking or corrosion beneath the coating (Correct answer)
- Immediate vessel shutdown for replacement
- Application of a new protective coating without further investigation
- Documentation only, as blistering is cosmetic
Correct answer: Further NDE such as UT or MT to evaluate for possible cracking or corrosion beneath the coating
Blistering near welds can indicate disbonded coating over corrosion or stress corrosion cracking, warranting follow-up NDE.
Question 3: A pressure vessel inspector uses acoustic emission (AE) testing during a hydrostatic pressure test. What does a cluster of AE activity at a specific location most likely indicate?
- Active crack growth or significant stress concentration at that location (Correct answer)
- Uniform general corrosion across the shell
- Proper seating of the vessel flanges
- Background noise from the pressurization pump
Correct answer: Active crack growth or significant stress concentration at that location
Clustered AE signals at a specific location suggest active crack propagation or significant plastic deformation, requiring follow-up NDE.
Question 4: When evaluating a pressure vessel shell with shear-wave UT, the inspector sets refracted angle at 45°. In which material condition would a 60° probe be preferred over 45°?
- When the weld has a steep bevel or narrow groove geometry where 45° beams cannot adequately illuminate the fusion line (Correct answer)
- When inspecting for laminations parallel to the surface
- When the material thickness exceeds 4 inches
- When inspecting austenitic welds with coarse grain structure
Correct answer: When the weld has a steep bevel or narrow groove geometry where 45° beams cannot adequately illuminate the fusion line
Steep-bevel narrow welds are better interrogated with a 60° beam that can more effectively sweep the near-vertical fusion faces.
Question 5: Under API 510, which condition requires an inspector to recommend a fitness-for-service (FFS) assessment rather than routine repair?
- A crack-like flaw detected by UT in a high-cycle fatigue service vessel (Correct answer)
- Minor surface rust on external insulation banding
- A small scratch on a non-pressure nameplate
- Paint peeling on the skirt support
Correct answer: A crack-like flaw detected by UT in a high-cycle fatigue service vessel
Crack-like flaws in fatigue service require API 579 FFS assessment to determine remaining life and acceptability before continuing operation.
Question 6: What is the significance of the 'dead band' or 'screen distance' setting when calibrating a straight-beam UT instrument for thickness measurement on a pressure vessel?
- It sets the near-surface zone where the instrument cannot reliably distinguish the front-wall echo from the back-wall echo (Correct answer)
- It defines the maximum measurable wall thickness range
- It establishes the search unit's transducer frequency
- It controls the ultrasonic beam spread angle
Correct answer: It sets the near-surface zone where the instrument cannot reliably distinguish the front-wall echo from the back-wall echo
The dead band (initial pulse zone) near the surface limits the minimum measurable thickness because the initial pulse obscures near-surface reflections.
Question 7: When using magnetic flux leakage (MFL) to inspect a pressure vessel floor or shell, what type of defect is MFL least sensitive to?
- Planar cracks oriented parallel to the magnetic flux direction (Correct answer)
- Pitting corrosion on the inspection surface
- Metal loss on the opposite surface
- Surface-breaking cracks perpendicular to the flux
Correct answer: Planar cracks oriented parallel to the magnetic flux direction
MFL is insensitive to planar defects that run parallel to the flux lines because they do not disrupt the flux path enough to create a detectable leakage field.
API 510 Inspection Methods & Nondestructive Testing 3
During phased array ultrasonic testing (PAUT) of a pressure vessel weld, what does the S-scan (sectorial scan) display show?