Individual Jurisdictions will have laws governing repairs to pressure vessels. In most cases they refer to the NBIC and the organization performing the repairs MUST have an "R" stamp.
I think the petroleum industry is different (suprise suprise) and may have some exceptions.
The NBIC may be able to provide a list of R stamp holders in your area. Any of the stamp holders can also let you know what must be done.
http://www.nationalboard.org/ may be something to look through.