Nice response Lawrence.
If I can add:
The intent of procedure qualification is to demonstrate the combination of welding process, base metal, filler metal, shielding gas, etc. will produce a weld that meet the minimum mechanical properties required by the welding standard. The test regiment for a grooved plate assembly is extensive and can includes: visual, NDE (AWS D1.1, D1.5, NAVSEA, etc.), guided bend tests, reduced section tensile testing, and notch toughness (when required).
The intent of performance qualification is to demonstrate the welder can deposit a sound weld when following a qualified or prequalified WPS (AWS D1.1, D1.5, etc.). The test regiment is abbreviated since there is no need to verified the WPS can produce the mechanical properties required by the welding standards.
The contractor must accept responsibility for both the procedure qualification and performance qualification. The contractor's signature in the space we typically call the certification is the activity performed by the contractor signifying they are accepting legal responsibility for the procedure qualification record, welding procedure specification, and or the performance qualification record.
Different welding standards invoke different requirements for qualifying the WPS and the welder. AWS D1.1 allows the Engineer to accept previous qualification for the welder and in the case of the WPS; if you purchase a license from AWS. Interesting that you can buy AWS' WPSs but they will not recognize a WPS qualified by another entity. Am I the only one that sees a conflict of interest with this arrangement?
ASME Section IX places the responsibility for qualifying the welder and the WPS squarely on the contractor's shoulders. Generally, ASME does not recognize qualification and certification by third parties such as an ATF or even AWS. Granted, there are exceptions, but usually the contractor has to supervise the welding of test coupon when qualifying the procedure or the welder.
Few welding standards require the WPS or the welder performance test be witnessed by a CWI. If CWI involvement is required, it is usually a customer imposed requirement.
Personal opinion: the CWI should only sign the test reports indicating what activities the CWI performed, i.e., witness the test, perform the visual, perform the NDE (when qualified to do so), and perform mechanical testing. Generally the CWI should not sign the certification statement unless the CWI is a direct employee of the contractor and the CWI is authorized to represent the contractor. In other words, a CWI that works for a third party and is not employed by the contractor should not sign the certification statement on behalf of the contractor.
Few CWIs understand the legal ramifications of signing performance test records, WPSs, or PQRs. As SCWI I witness the welding and I perform the tests used to evaluate the test assemblies. I sign for those activities, but I do not certify the welder or the WPS or PQR.
Best regards - Al