The weld on weld is not a bad thing. Think of a multiple pass weld. That is nothing more than one weld bead deposited on another. The potential for a problem is that the initial weld was made following a written WPS that was either prequalified or qualified by testing to verify the filler metal was compatible with the base metal, the proper preheat was used, etc.
It is dubious at best to believe the hanger was welded with the same level of scrutiny. Was a written procedure followed? Was the welder qualified? Was the hanger welds inspected once they were completed? You can see where this is going?
It is up to the owner to determine if the hanger is acceptable in the present state. The contractor that made the initial welds met his obligation once the owner (most likely a third party inspector representing the owner) accepted the welded joint. Anything done to the completed weld after the fact is beyond the original contractor's control. If there is a question on the quality of the hanger, the location of the hanger, welding to an existing weld, etc., it it is the owner's responsibility to get the issues resolved to their satisfaction.
As the owner, I would request the hanger be relocated; the weld ground to the original condition and some NDT, perhaps a liquid penetrant test performed after the area is ground smooth. I would also perform an acid etch after the penetrant test (not before because the acid entrapped by a crack can adversely affect the penetrant test results) to ensure the HAZ from the hanger is completely removed.
The owner should approve the new hanger location and the welding documents, i.e., WPS and welder performance test records, reviewed before the replacement hanger is welded in place.
Best regards - Al
