Modification of internal support rings in caustic service

[txcadman]

I am addressing an issue with a new vessel (1-3/8" wall thk, SA516-70 material) that has not been in operation. The vessel is PWHT and is in Caustic service. However the internal support rings were fabricated incorrectly. The modifications to the tray support rings will need to be made which will require PWHT. However the problem is that the trays require "seal welding in the field to be liquid tight". Can the trays be seal welded to the support rings with out effecting PWHT; even though the trays will be in contact with the service? Is there any direction in the NBIC in regards to internal support modifications to the pressure boundary?

 

[stanweld]

In caustic service where PWHT is absolutely required, I would advise PWHT after the defined repair.