If it is a code stamped vessel and you wish to maintain the code status, your repair will have to meet the requirements of the NBIC and you will have to involve an Authorized Inspector. When all is said an done, the "repaired" vessel will be as "good as new".
It isn't just a question of what thickness you should use and "slap on" a patch unless you are going to repurpose the vessel as an artificial coral reef.
Best regards - Al
By Joey
Date 01-25-2021 01:28
Edited 01-25-2021 01:32
hi
Your issue may be referred to API 510 that covers the in-service inspection, or repair of pressure vessels that have been placed in service. Here what API 510 says:
Fillet-welded Patches
8.1.6.1.2.1 Fillet-welded patches may be used to make temporary repairs to damaged, corroded, or eroded areas of
pressure vessel components. Cracks shall not be repaired in this manner unless the engineer determines that the cracks will not be expected to propagate from under the patch. In some cases, the engineer may need to perform a FFS analysis. Temporary repairs using fillet-welded patches shall be approved by an inspector and engineer.
API 510 never stated the minimum thickness of the patch plate, my guess is the thickness should not be lower than the required min thickness + the corrosion allowance. However, you need to get this information from the Pressure Vessel Engineer.
7.6 Required Thickness Determination
The required thickness shall be based on pressure, mechanical, and structural considerations using the appropriate
design formulae and code allowable stress. For services with high potential consequences if failure were to occur, the
engineer should consider increasing the required thickness above the calculated minimum thickness to provide for
unanticipated or unknown loadings, undiscovered metal loss, or resistance to normal abuse.
Hope the above helps.
Joey