API 510 Inspection Techniques & Nondestructive Testing 5 — Questions and Answers
Question 1: Infrared thermography (IRT) is used during pressure vessel inspection to detect:
- Precise weld fusion line defects in austenitic stainless steel
- Hot spots in refractory-lined vessels indicating lining failure or thinning (Correct answer)
- Hydrogen embrittlement in high-strength steel components
- Chloride stress corrosion cracking under insulation
Correct answer: Hot spots in refractory-lined vessels indicating lining failure or thinning
IRT detects thermal anomalies; hot spots on externally insulated or refractory-lined vessels indicate areas of lining degradation or local overheating where the protective layer has failed.
Question 2: A vessel inspector conducting a radiographic examination notes 'scattered porosity' in a weld radiograph. How is scattered porosity typically evaluated per ASME Section VIII, Division 1?
- It is always cause for rejection regardless of individual pore size
- It is compared against acceptance charts that consider pore size, density, and distribution (Correct answer)
- Only the largest individual pore diameter is measured for acceptance
- Scattered porosity is acceptable in all welds unless pores are clustered
Correct answer: It is compared against acceptance charts that consider pore size, density, and distribution
ASME acceptance criteria for porosity use charts correlating weld thickness, individual pore size, and the number of pores in a given length to determine acceptability.
Question 3: During time-of-flight diffraction (TOFD) ultrasonic inspection, the lateral wave is used to:
- Detect mid-wall laminations running parallel to the surface
- Serve as a timing reference for calculating flaw depth and height (Correct answer)
- Indicate the back-wall surface position for thickness measurement
- Identify surface-breaking cracks on the far wall
Correct answer: Serve as a timing reference for calculating flaw depth and height
In TOFD, the lateral wave travels along the surface at a known velocity and serves as a precise timing reference, enabling accurate depth sizing of detected flaws.
Question 4: When inspecting a pressure vessel that has experienced high-temperature hydrogen attack (HTHA), the NDT method that can detect the internal microstructural damage (methane voids and fissures) most effectively is:
- Conventional radiography
- Automated ultrasonic testing using creeping wave or TOFD techniques (Correct answer)
- Magnetic particle testing with AC yoke
- Liquid penetrant testing with color contrast method
Correct answer: Automated ultrasonic testing using creeping wave or TOFD techniques
HTHA produces internal methane-filled voids and micro-fissures that conventional methods miss; advanced UT techniques such as TOFD and creeping wave UT can detect this subsurface volumetric damage.
Question 5: Per API 510, what action is required when the calculated remaining life of a pressure vessel is less than 4 years?
- The vessel must be immediately taken out of service for repair
- The next internal or on-stream inspection interval must not exceed half the remaining life (Correct answer)
- A fitness-for-service assessment must be performed within 30 days
- The maximum allowable working pressure must be reduced by 10%
Correct answer: The next internal or on-stream inspection interval must not exceed half the remaining life
API 510 requires that when remaining life is less than 4 years, the next inspection interval shall not exceed half the remaining life to ensure the vessel is re-evaluated before reaching minimum thickness.
Question 6: Positive material identification (PMI) is most critical during vessel inspection when:
- Verifying that the nameplate data matches the original design drawings
- Confirming that replacement materials and weld filler metals are the correct specified alloy (Correct answer)
- Checking that all bolting torque values meet code requirements
- Ensuring hydrostatic test water meets chemical purity standards
Correct answer: Confirming that replacement materials and weld filler metals are the correct specified alloy
PMI ensures replacement components and welds use the correct alloy, preventing material mix-ups that could cause brittle fracture, stress corrosion cracking, or other failures in service.
Question 7: A near-drum inspection of a pressure vessel reveals a 'turtle-back' bulge on the shell. This morphology is most characteristic of which damage mechanism?
- External stress corrosion cracking from chloride exposure
- Hydrogen-induced blistering from wet hydrogen sulfide service (Correct answer)
- Thermal fatigue from cyclic temperature fluctuations
- Erosion-corrosion from high-velocity liquid impingement
Correct answer: Hydrogen-induced blistering from wet hydrogen sulfide service
Turtle-back or dome-shaped bulges on the pressure vessel shell are classic indicators of hydrogen blistering, where hydrogen atoms recombine as H₂ gas within laminations and push the metal outward.
API 510 Inspection Techniques & Nondestructive Testing 5
Infrared thermography (IRT) is used during pressure vessel inspection to detect: