API 510 Repair, Alteration & Rerating Procedures 5 — Questions and Answers
Question 1: API 510 states that the inspector should review which documents before approving a repair involving welding?
- Only the repair contractor's insurance certificate
- Welding procedure specifications (WPS), welder qualifications, and the repair plan (Correct answer)
- The vessel's original purchase order only
- The plant safety manual and emergency response plan
Correct answer: Welding procedure specifications (WPS), welder qualifications, and the repair plan
Before approving welded repairs, the inspector must review and verify the WPS, welder performance qualifications, and the overall repair plan.
Question 2: A steel pressure vessel shell has corroded to a thickness below the minimum required. The owner plans to restore it by welding a full encirclement sleeve. This is considered a:
- Minor maintenance activity
- Temporary repair only, valid for one inspection interval
- Permanent repair if designed and executed to applicable code requirements (Correct answer)
- Cosmetic enhancement not subject to inspection
Correct answer: Permanent repair if designed and executed to applicable code requirements
A properly designed and installed full encirclement sleeve welded per applicable code can be a permanent repair restoring pressure-containing integrity.
Question 3: Under API 510, when does a change in service fluid (e.g., from water to a lethal gas) require the vessel to be treated as an alteration?
- Any change in service fluid is automatically an alteration
- When the new service results in more severe conditions not covered by the original design or code requirements (Correct answer)
- Only when the new fluid is corrosive
- Only when the operating temperature changes by more than 50°F
Correct answer: When the new service results in more severe conditions not covered by the original design or code requirements
A service change is an alteration when the new conditions (pressure, temperature, corrosivity, or lethal service classification) exceed the original design intent.
Question 4: After completing an alteration, the 'R' stamp holder must update the nameplate to show:
- The repair contractor's name and address
- The new MAWP, temperature, and the 'R' stamp number with the alteration year (Correct answer)
- Only the alteration date
- The name of the authorized inspector only
Correct answer: The new MAWP, temperature, and the 'R' stamp number with the alteration year
Following an alteration, the nameplate must be updated to reflect the revised MAWP, temperature rating, and the R-stamp holder's mark with the year of alteration.
Question 5: When calculating the MAWP for rerating a vessel shell, the inspector uses the 'actual measured thickness' rather than the nominal thickness because:
- Nominal thickness always overstates the actual metal available after corrosion and mill tolerance (Correct answer)
- Regulations prohibit the use of nominal thickness in any calculation
- Actual thickness is always thicker than nominal due to manufacturing tolerances
- ASME code requires only nominal thickness for new construction, not repairs
Correct answer: Nominal thickness always overstates the actual metal available after corrosion and mill tolerance
After service, corrosion and mill under-tolerance reduce wall thickness below nominal, so the actual measured value provides a more accurate and conservative MAWP.
Question 6: API 510 requires that any hot-tap performed on an in-service pressure vessel be:
- Restricted to vessels with MAWP below 150 psi
- Evaluated and approved by the authorized inspector and supported by engineering analysis (Correct answer)
- Performed only when the vessel is fully depressurized
- Prohibited on all pressure vessels without exception
Correct answer: Evaluated and approved by the authorized inspector and supported by engineering analysis
Hot-tapping on in-service vessels requires engineering evaluation of risks and explicit approval by the authorized inspector before proceeding.
Question 7: A vessel was originally built with a joint efficiency (E) of 0.70 (spot radiographed). If during rerating the inspector upgrades the joint efficiency to 1.0 by performing full radiography of all welds, the MAWP will:
- Remain unchanged because joint efficiency does not affect MAWP
- Decrease because more scrutiny reveals more defects
- Increase because the allowable stress is effectively higher at E=1.0 (Correct answer)
- Double because joint efficiency is a multiplier applied to the safety factor
Correct answer: Increase because the allowable stress is effectively higher at E=1.0
MAWP is directly proportional to joint efficiency (E); upgrading from E=0.70 to E=1.0 through full radiography increases the calculated MAWP by approximately 43%.
API 510 Repair, Alteration & Rerating Procedures 5
API 510 states that the inspector should review which documents before approving a repair involving welding?