tankerator
Mechanical
Per API 650 section 5.7.4.2 and 5.7.4.3, certain shell nozzle penetrations require PWHT depending on material group, shell thickness, and nozzle size. When that is the case, "openings...shall be prefabricated into the shell plate or thickened insert plate and the prefabricated assembly shall be thermally stress relieved...prior to installation."
This requirement is pretty cut and dry on a new tank but when API 653 is consulted regarding nozzle replacement on an existing tank, you are referred to the current standard of 650. Does that mean that if I have an existing tank that requires a shell nozzle replacement, I need to remove a larger portion of the shell(say 3'x3'), weld the nozzle into that 3'x3' insert plate, PWHT, butt weld the insert assembly into the shell, and then weld a repad onto it? It might be easier to do that for a thickened insert plate assembly but those are not preferred in my refinery. The section of referenced above does not seem to make an allowance for repads in the even of replacement.
Any help or opinions on the matter would be appreciated.
Thanks!
This requirement is pretty cut and dry on a new tank but when API 653 is consulted regarding nozzle replacement on an existing tank, you are referred to the current standard of 650. Does that mean that if I have an existing tank that requires a shell nozzle replacement, I need to remove a larger portion of the shell(say 3'x3'), weld the nozzle into that 3'x3' insert plate, PWHT, butt weld the insert assembly into the shell, and then weld a repad onto it? It might be easier to do that for a thickened insert plate assembly but those are not preferred in my refinery. The section of referenced above does not seem to make an allowance for repads in the even of replacement.
Any help or opinions on the matter would be appreciated.
Thanks!