Nozzle Flange modification in API 650 Tank (Post hydrotest tank)

[siva_mech]

I have an issue with the bolt hole orientation of a nozzle flange. Construction has not taken care to straddle the bolt hole orientation with the vertical centerlines of the tank. The mixer flange when tried to fit with the tank nozzle flange, the bolt holes were offset by 20 mm. Now we want to cut the flange, rotate the re fit-up the flange and weld it. I want to know the acceptance clauses in API-650 & API-653 to support this to get client approval.

 

[JStephen]

I don't think you'll find this well addressed in either standard.
First off, note that API-653 applies only to tanks that have gone into service, IE, have had product in them. That said, you could look into what does or does not constitute a "major repair" that requires a re-hydrotest per API-653.
API-650 gives you an option to omit hydrotesting with other kinds of testing. It doesn't say you can do half-and-half, but there's no logical reason that couldn't be done- it's be an owner call as to the acceptability of that.
Simplest solution if conditions permitted would be to fab up an adapter spool with two flanges rotated by the appropriate amount.