API 510 Inspection Techniques & Nondestructive Testing 4 — Questions and Answers
Question 1: A hydrogen-induced cracking (HIC) inspection of a carbon steel vessel operating in wet H₂S service should prioritize which NDT technique?
- Shear wave UT angle beam scanning of welds
- Straight beam UT or phased array UT to detect internal laminar cracking (Correct answer)
- Fluorescent liquid penetrant testing of external surfaces
- Radiography of base metal away from welds
Correct answer: Straight beam UT or phased array UT to detect internal laminar cracking
HIC produces internal laminar cracks parallel to the plate surface; straight beam UT effectively detects these by identifying loss of back-wall reflection or anomalous mid-wall indications.
Question 2: Guided wave ultrasonic testing (GWUT) is used in pressure vessel piping inspections primarily to:
- Provide precise wall thickness at individual measurement points
- Screen long lengths of pipe for corrosion anomalies from a single probe position (Correct answer)
- Detect surface-breaking weld cracks in high-alloy piping
- Replace radiography for butt weld volumetric examination
Correct answer: Screen long lengths of pipe for corrosion anomalies from a single probe position
GWUT propagates low-frequency waves along the pipe axis, allowing a single probe to screen tens of meters of pipe for corrosion, erosion, or other wall-loss anomalies.
Question 3: When using phased array ultrasonic testing (PAUT) for weld inspection, which advantage does it offer over conventional single-element UT?
- Eliminates the need for calibration reference blocks
- Provides multiple beam angles simultaneously with electronic scanning (Correct answer)
- Is effective on all materials including nonconductive polymers
- Requires no couplant between the probe and test surface
Correct answer: Provides multiple beam angles simultaneously with electronic scanning
PAUT electronically steers and focuses multiple beam angles without physically moving the probe, enabling faster scanning and improved flaw characterization compared to single-element UT.
Question 4: During an internal visual inspection of a pressure vessel, the inspector observes a deposit of orange-brown scale on the bottom head. The most likely cause and recommended follow-up is:
- Erosion from high-velocity flow; perform UT on adjacent nozzles
- Iron oxide from general corrosion; perform UT thickness readings under and near the deposit (Correct answer)
- Sulfur deposits from product contamination; clean and perform PT on head
- Biological fouling; flush with biocide and re-inspect visually
Correct answer: Iron oxide from general corrosion; perform UT thickness readings under and near the deposit
Orange-brown scale is typically iron oxide corrosion product; UT should be performed under and around the deposit to quantify metal loss beneath it.
Question 5: What does the term 'remaining life' mean in the context of API 510 inspection planning?
- The calendar time since the vessel was last hydrostatically tested
- The estimated time before the vessel wall reaches minimum allowable thickness at the measured corrosion rate (Correct answer)
- The number of inspection cycles remaining before mandatory replacement
- The time until the vessel's code stamp must be recertified
Correct answer: The estimated time before the vessel wall reaches minimum allowable thickness at the measured corrosion rate
Remaining life is calculated by dividing the difference between current thickness and minimum allowable thickness by the corrosion rate, giving the estimated time before retirement.
Question 6: Thermoelectric (spark) testing is sometimes used during vessel fabrication inspection to verify:
- Weld bead geometry meets drawing dimensions
- That the correct alloy material has been used (positive material identification) (Correct answer)
- Residual stress levels in heat-affected zones
- Hardness of weld overlays meets minimum requirements
Correct answer: That the correct alloy material has been used (positive material identification)
Thermoelectric testing (along with XRF and OES) is a form of positive material identification (PMI) that distinguishes alloy families by their thermoelectric signature against a reference material.
Question 7: An inspector is evaluating a pressure vessel for fitness-for-service after finding a blister from hydrogen damage. Per API 579-1/ASME FFS-1, the first assessment level for HIC/SOHIC involves:
- Performing a detailed stress analysis using finite element modeling
- Applying screening criteria based on blister dimensions relative to vessel geometry (Correct answer)
- Cutting out the affected area and performing destructive metallurgical analysis
- Conducting a hydrostatic test at 1.5 times design pressure immediately
Correct answer: Applying screening criteria based on blister dimensions relative to vessel geometry
Level 1 FFS assessment for HIC/blistering uses prescriptive screening rules comparing blister size, depth, and proximity to welds against acceptance criteria without requiring complex stress analysis.
API 510 Inspection Techniques & Nondestructive Testing 4
A hydrogen-induced cracking (HIC) inspection of a carbon steel vessel operating in wet H₂S service should prioritize which NDT technique?