API 510 Pressure Vessel Design & Inspection Codes 5 — Questions and Answers
Question 1: According to API 510, post-weld heat treatment (PWHT) of a repair weld may be waived under certain conditions. Which factor most commonly allows this waiver?
- The weld is made during daytime hours only
- The base metal P-number, wall thickness, and preheat meet the exemption criteria in the construction code (Correct answer)
- The vessel has been in service for more than 10 years
- The repair is made with a low-hydrogen electrode only
Correct answer: The base metal P-number, wall thickness, and preheat meet the exemption criteria in the construction code
PWHT waivers are based on material P-number, thickness, preheat temperature, and other criteria specified in the original construction code such as ASME VIII.
Question 2: Under ASME Section VIII Division 1, what is the minimum required thickness for a flat head cover versus a hemispherical head of the same diameter and design pressure?
- Flat heads require significantly more thickness because they resist pressure by bending rather than membrane action (Correct answer)
- Flat heads require less thickness because they have no curvature to cause stress concentration
- Both require identical thickness under ASME VIII rules
- Flat heads require the same thickness as 2:1 ellipsoidal heads
Correct answer: Flat heads require significantly more thickness because they resist pressure by bending rather than membrane action
Flat heads must resist pressure by bending, which is far less efficient than the membrane (hoop) stress action in curved heads, requiring substantially greater thickness.
Question 3: According to API 510, what is a 'rerating' of a pressure vessel?
- A routine recertification of the vessel's nameplate data
- A change to the established MAWP or temperature rating of the vessel (Correct answer)
- The process of repainting and re-inspecting the vessel exterior
- The replacement of all pressure-retaining parts of the vessel
Correct answer: A change to the established MAWP or temperature rating of the vessel
Rerating is a formal change to the vessel's MAWP or design temperature, either upward or downward, based on engineering calculations and inspection findings.
Question 4: When API 510 refers to 'on-stream inspection,' what primary technique is used to assess internal corrosion without vessel entry?
- Visual inspection through open manholes with the vessel pressurized
- Ultrasonic thickness measurement from the external surface (Correct answer)
- Radiographic examination requiring personnel inside the vessel
- Pressure testing to confirm the vessel holds design pressure
Correct answer: Ultrasonic thickness measurement from the external surface
Ultrasonic thickness (UT) scanning from the outside is the primary on-stream method for measuring wall thickness and detecting internal corrosion without vessel entry.
Question 5: In ASME VIII Division 1, the 'U' stamp on a pressure vessel certifies that:
- The vessel has passed its most recent API 510 inspection
- The vessel was fabricated in accordance with ASME Section VIII Division 1 requirements (Correct answer)
- The vessel has been repaired under the National Board 'R' stamp program
- The vessel is rated for ultra-high pressure service above 3,000 psi
Correct answer: The vessel was fabricated in accordance with ASME Section VIII Division 1 requirements
The ASME 'U' stamp indicates the vessel was designed, fabricated, inspected, and tested per ASME Section VIII Division 1, with a certified manufacturer's data report.
Question 6: According to API 510, which document records the vessel's design data, material specifications, and inspection history and must be maintained by the owner/operator?
- The National Board Inspection Code (NBIC)
- The vessel inspection record and documentation file (Correct answer)
- The piping and instrumentation diagram (P&ID)
- The process hazard analysis (PHA) report
Correct answer: The vessel inspection record and documentation file
API 510 requires the owner/operator to maintain vessel inspection records including design data, inspection findings, repairs, and alterations throughout the vessel's service life.
Question 7: Under ASME VIII Division 1, which head type is considered the code standard and typically used as the basis for most shell-and-tube heat exchanger channel closures?
- Hemispherical heads
- 2:1 semi-ellipsoidal heads (Correct answer)
- Flat heads
- Toriconical heads
Correct answer: 2:1 semi-ellipsoidal heads
The 2:1 semi-ellipsoidal head is the standard ASME VIII head type widely used in industrial vessels including heat exchanger channels due to its balance of efficiency and fabrication practicality.
API 510 Pressure Vessel Design & Inspection Codes 5
According to API 510, post-weld heat treatment (PWHT) of a repair weld may be waived under certain conditions.
Which factor most commonly allows this waiver?