Under API-653, 12.3.1 When Hydrostatic Testing is required, then 12.3.1.2.e. It states "When removal and replacement of any part of the weld attaching the shell to the bottom or to the annular plate ring."
But then under 12.3.2 When hydrostatic Testing is Not Required. See 12.3.2.4.1.a. and b...
According to API 510, Section 7.2.7, Fillet weld lap patches are acceptable for temporary repairs after being approved by experienced pressure vessel engineer. What calculations need to be done to evaluate and approve such a repair?
API 510 lists:
1. Allowable membrane stress not exceeded...
