Hi Ziggy,
I'll assume you're inspecting after the fact, rather than during production. First, I can't recall ever seeing anything in any contract specifications addressing additional inspection of studs. To me, testing a "reasonable number of additional studs" would mean testing enough studs to assure me that they are now meeting code requirements after initial failures have been discovered. The more failures found, obviously the more frequent the number of studs that are tested. When it gets to that point, then it's time to notify the EOR. If, in the judgement of the EOR, the studs welded are not in accordance with code provisions as indicated by inspection and testing, corrective action would be required of the contractor at his expense. To ensure that subsequent welds will meet code requirements, corrective action may include changes to the welding procedure, welding equipment, or stud base. The contractor may be required to submit samples of the studs so that the validity of the manufacturers certs of stud base weldability can be verified.