API 510 Repair, Alteration & Rerating Procedures 3 — Questions and Answers
Question 1: Under API 510, when can PWHT be waived for a repair weld on a vessel that originally required PWHT?
- When the repair is smaller than 2 inches in any dimension
- When approved by the API 510 inspector and supported by engineering analysis or code alternatives (Correct answer)
- When the vessel has been in service for more than 20 years
- PWHT can never be waived if it was required originally
Correct answer: When approved by the API 510 inspector and supported by engineering analysis or code alternatives
PWHT may be waived when alternative measures are approved by the inspector and justified by engineering analysis or applicable code provisions.
Question 2: A vessel alteration changes the design pressure from 150 psi to 200 psi. According to API 510, the rerating:
- Is considered a minor alteration requiring no additional calculations
- Requires an engineering review to verify the vessel is suitable for the higher pressure (Correct answer)
- Can be approved by the plant engineer without inspector involvement
- Is only valid if the original vessel was built to ASME Section VIII Division 2
Correct answer: Requires an engineering review to verify the vessel is suitable for the higher pressure
Any rerating to higher pressure requires engineering calculations verifying that all components can safely handle the new MAWP.
Question 3: What is the purpose of a hydrostatic test following a major repair or alteration under API 510?
- To confirm the original design pressure is still valid
- To verify the repair integrity and absence of leaks under pressure (Correct answer)
- To satisfy insurance company requirements only
- To determine the remaining corrosion allowance
Correct answer: To verify the repair integrity and absence of leaks under pressure
Post-repair hydrostatic testing verifies the structural integrity of the repaired area and ensures there are no leaks.
Question 4: When is a pneumatic test permitted instead of a hydrostatic test after a repair, per API 510?
- Whenever the inspector prefers pneumatic testing
- When the vessel design or support structure cannot support the water weight, and precautions are taken for the hazard (Correct answer)
- Pneumatic tests are never permitted as an alternative to hydrostatic tests
- When the vessel will be used for gas service only
Correct answer: When the vessel design or support structure cannot support the water weight, and precautions are taken for the hazard
Pneumatic tests may substitute for hydrostatic tests when filling with water is impractical, but additional safety precautions are required due to the stored energy hazard.
Question 5: Under NBIC and API 510, a 'repair' is distinguished from an 'alteration' because a repair:
- Always involves welding, whereas an alteration may not
- Restores a vessel to its original design condition without changing its pressure-temperature rating or configuration (Correct answer)
- Must be performed by the original manufacturer
- Requires less documentation than an alteration
Correct answer: Restores a vessel to its original design condition without changing its pressure-temperature rating or configuration
A repair restores a vessel to its original design condition, while an alteration changes a design parameter such as MAWP, temperature, or configuration.
Question 6: When adding a nozzle to an existing pressure vessel (an alteration), the reinforcement calculations must account for:
- Only the nozzle wall thickness
- The opening in the shell, nozzle neck, and any reinforcing pad contribution (Correct answer)
- The total vessel surface area only
- The original design factor of safety without recalculation
Correct answer: The opening in the shell, nozzle neck, and any reinforcing pad contribution
Reinforcement area calculations for a new nozzle must consider the material removed from the shell, the nozzle neck thickness, and any reinforcing pad area.
Question 7: API 510 specifies that temporary repairs such as leak boxes or enclosures must be:
- Removed within 30 days of installation
- Approved by the inspector and have a defined plan for permanent repair (Correct answer)
- Limited to non-pressure-containing welds only
- Installed only by the vessel's original manufacturer
Correct answer: Approved by the inspector and have a defined plan for permanent repair
Temporary repairs must be reviewed and approved by the authorized inspector with documentation of the timeline and plan for permanent correction.
API 510 Repair, Alteration & Rerating Procedures 3
Under API 510, when can PWHT be waived for a repair weld on a vessel that originally required PWHT?