API 510 Repair, Alteration & Rerating Procedures 4 — Questions and Answers
Question 1: According to API 510, weld overlay (cladding restoration) on a corroded vessel shell is classified as a:
- Cosmetic repair not subject to code requirements
- Repair requiring WPS qualification and authorized inspector involvement (Correct answer)
- Minor maintenance activity exempt from PWHT requirements
- Structural alteration requiring full vessel rerating
Correct answer: Repair requiring WPS qualification and authorized inspector involvement
Weld overlay to restore corroded pressure-containing areas is a repair that requires qualified welding procedures and authorized inspector oversight.
Question 2: A pressure vessel owner wants to lower the MAWP of a vessel (rerate downward). Under API 510, this:
- Requires the same engineering rigor as a rerating upward
- Is generally straightforward and requires updating the nameplate and records (Correct answer)
- Is not permitted under any circumstances
- Requires a full hydrostatic test at the new lower pressure
Correct answer: Is generally straightforward and requires updating the nameplate and records
Rerating to a lower MAWP is generally a simpler process but still requires updated documentation, nameplate changes, and notification to the inspector.
Question 3: When a repair is made by welding on a vessel in hydrogen service, which additional concern must be addressed?
- Hydrogen embrittlement risk and the need for bake-out procedures before welding (Correct answer)
- The use of stainless steel filler metal only
- A minimum preheat of 400°F regardless of material
- Mandatory radiography of the entire vessel shell
Correct answer: Hydrogen embrittlement risk and the need for bake-out procedures before welding
Vessels in hydrogen service risk hydrogen-induced cracking; bake-out (degassing) before welding and careful preheat/PWHT practices are essential.
Question 4: Under API 510, which document establishes the minimum requirements for repair organizations performing welded repairs on pressure vessels?
- ASME B31.3
- The National Board Inspection Code (NBIC) (Correct answer)
- API RP 579
- API Standard 653
Correct answer: The National Board Inspection Code (NBIC)
The NBIC (National Board Inspection Code) establishes the minimum requirements for repair organizations, including those holding the National Board 'R' stamp.
Question 5: After a repair, the inspector records the work on which form when using the National Board program?
- NB Form R-1 (Report of Repair) (Correct answer)
- ASME Form U-1 (Manufacturer's Data Report)
- API Form 510-A (Inspection Record)
- OSHA Form 300 (Incident Log)
Correct answer: NB Form R-1 (Report of Repair)
National Board Form R-1 is the official repair report that must be completed and filed for pressure vessel repairs under the R-stamp program.
Question 6: When performing a rerating calculation for a cylindrical shell under internal pressure using API 510, the formula used is based on:
- The original material mill certification only
- ASME Section VIII Division 1 thickness and stress equations for the shell (Correct answer)
- A simplified factor of 4:1 safety ratio applied to the test pressure
- The original purchase order specifications
Correct answer: ASME Section VIII Division 1 thickness and stress equations for the shell
MAWP calculations for cylindrical shells use the ASME Section VIII Div. 1 hoop stress equations, considering current thickness, allowable stress, and joint efficiency.
Question 7: A repair organization proposes to use a weld procedure not qualified to the current code edition for a vessel repair. Under API 510, this is:
- Acceptable if the welder has 10+ years experience with that procedure
- Unacceptable; all WPS must be qualified per an applicable welding code (Correct answer)
- Acceptable for minor repairs under 6 inches in length
- At the discretion of the plant maintenance supervisor
Correct answer: Unacceptable; all WPS must be qualified per an applicable welding code
All welding on pressure vessels must be performed using WPS qualified to an applicable welding code such as ASME Section IX, regardless of welder experience.
API 510 Repair, Alteration & Rerating Procedures 4
According to API 510, weld overlay (cladding restoration) on a corroded vessel shell is classified as a: