API 510 Material Evaluation 2 — Questions and Answers
Question 1: When evaluating a pressure vessel for hydrogen-induced cracking (HIC), which metallurgical factor most significantly influences susceptibility?
- High manganese content in the steel
- Sulfur content and sulfide inclusion morphology (Correct answer)
- Carbon equivalent above 0.43
- Elevated silicon content
Correct answer: Sulfur content and sulfide inclusion morphology
Sulfide inclusions, particularly elongated MnS inclusions, are the primary initiation sites for HIC in pressure vessel steels.
Question 2: An API 510 inspector is reviewing mill test reports (MTRs) for a replacement shell course. Which property must be verified to confirm the material meets ASME Section II requirements?
- Only the tensile strength
- Yield strength, tensile strength, and elongation (Correct answer)
- Hardness and impact values only
- Carbon equivalent only
Correct answer: Yield strength, tensile strength, and elongation
MTRs must confirm yield strength, tensile strength, and elongation as minimum mechanical properties per ASME Section II requirements.
Question 3: A carbon steel vessel operating in wet H2S service shows blistering on the internal surface. What is the primary mechanism causing this damage?
- Stress corrosion cracking from chlorides
- Atomic hydrogen diffusing into the steel and recombining at discontinuities (Correct answer)
- High-temperature hydrogen attack above 400°F
- Caustic stress corrosion cracking
Correct answer: Atomic hydrogen diffusing into the steel and recombining at discontinuities
In wet H2S service, atomic hydrogen diffuses into the steel and recombines as molecular hydrogen at internal voids, creating blisters through pressure buildup.
Question 4: According to API 510, what action is required when the actual material of a vessel component cannot be positively identified?
- Assume SA-516-70 and proceed with inspection
- Test the material using PMI or other methods, or assume the lowest-grade material (Correct answer)
- Remove the component immediately
- Contact the original manufacturer only
Correct answer: Test the material using PMI or other methods, or assume the lowest-grade material
When material cannot be identified, API 510 requires PMI or other testing, or the inspector must assume the lowest-strength material for calculations.
Question 5: A vessel fabricated from SA-387 Grade 11 (1.25Cr-0.5Mo) steel is being evaluated after long-term service at 850°F. What material degradation mechanism is the primary concern?
- Graphitization
- Temper embrittlement (Correct answer)
- Sigma phase formation
- Sensitization
Correct answer: Temper embrittlement
Cr-Mo steels in the temperature range of 650-1100°F are susceptible to temper embrittlement from segregation of tramp elements to grain boundaries.
Question 6: When using Positive Material Identification (PMI) to verify alloy content, which technique provides elemental analysis that can detect carbon content?
- X-ray fluorescence (XRF)
- Optical emission spectrometry (OES) (Correct answer)
- Eddy current testing
- Magnetic permeability measurement
Correct answer: Optical emission spectrometry (OES)
OES (spark testing) can detect carbon content, while XRF cannot reliably measure carbon due to the low atomic number limitation of most portable XRF units.
Question 7: A reactor vessel in high-temperature hydrogen service is being evaluated against the Nelson Curves. The operating condition falls above the applicable curve. What does this indicate?
- The vessel is safe for continued operation
- The material is susceptible to high-temperature hydrogen attack (HTHA) (Correct answer)
- The vessel requires immediate shutdown for stress relief
- The hydrogen partial pressure is within acceptable limits
Correct answer: The material is susceptible to high-temperature hydrogen attack (HTHA)
Operating above the Nelson Curve for a given material indicates susceptibility to HTHA, where hydrogen reacts with carbides causing decarburization and fissuring.
API 510 Material Evaluation 2
When evaluating a pressure vessel for hydrogen-induced cracking (HIC), which metallurgical factor most significantly influences susceptibility?