Each code, while similar in many ways, are different from other codes. The differences may be the width or thickness of the samples subjected to a guided bend test, the dimensions of the reduced section tensile test, or nick break tests are required instead of the guided bend tests. One code may require the welded coupon be X-rayed before the mechanical testing or it may allow UT be used in lieu of RT, or no volumetric testing is needed. So, qualification is usually done to a particular code.

There are some codes that recognize a "mock-up" of the weld used in production. In short, a production piece is subjected to a regiment of tests as described by the applicable code or per the customer's direction. Not all codes recognize this method of qualification.

There are cases where there is no code that applies to the specific application. When that is the case the contractor or customer can decide to adopt a welding standard is "good enough" or they may develop a methodology that provides the data indicating the weld is "good enough" for that application.

Ultimately, it is the Owner that has the responsibility to determine how the welds are going to be qualified, examined, and the acceptance criteria that will be applied. The Owner can either elect to use an industry recognized welding standard or they can develop their own. The exception is when there is a legal requirement that must be satisfied. For instance, for buildings we have the "building code" that is adopted either at the state level or municipal level. That is a legal obligation. The building code will reference the design and fabrication codes that stipulate how the WPS is be qualified.

Some codes recognize prequalified WPSs that are not supported by a PQR. Some codes recognize Standard WPSs that are backed up with PQRs. In some cases the WPS has to be supported by actual testing that demonstrates the welds meet the minimum requirements of the "code."

In short, there is no one answer that is correct in all circumstances.

Al