According to the following link, that standard has been withdrawn.
My experience with the API Standards (excluding API 1104) has been that they generally allow weld procedure and performance qualifications in accordance with ASME Section IX.
If it was me, I would suggest that to the client's engineering repa and see where it leads.
http://www.techstreet.com/cgi-bin/detail?product_id=35174
Charles.
You could also look into API 618 and see if there is any guidance that may be applicable to your situation.