A prequalified welding procedure specification is one where it has been agreed that a welding procedure qualification test need not be performed either because an existing procedure qualification record is deemed acceptable or because there are standard, prequalified welding procedure specifications referenced by the code in use for the welding operation.
I would second what Sjones said, but add that the effective throats (most important for partial pen welds) is "given" to you based on meeting the criteria for the prequalification.
The significance of a prequalified WPS is all dependant on the welding qualification code being used. Codes such as AWS D1.1 and D1.5, etc, allow prequalified procedures if all of the rules in the code that are specified requriements for prequalified welding procedures. Other codes (Such as ASME Section IX), do not allow the use of prequalified welding procedures. Section IX does allow the use of specific AWS SWPSs though.
A prequalified welding procedure does not require qualification by testing that may include both NDT and destructive mechanical testing of a welded test coupon.
Not all welding standard or codes accept the concept of prequalified welding procedures and they require the contractor to weld a sample that is subjected to various tests to prove the mechanical properties and soundness requirements of the appropriate standard are met.
The specific requirements or conditions that have to be met to be prequalified are dependent on the specific welding standard or code being used. For instance, AWS D1.1 lists the welding processes, base metals, filler metal requirements, joint details, fabrication requirements, inspection requirements, and acceptance criteria that must be met in order to be a prequalified welding process. If any of the conditions are not met, the procedure is not deemed prequalified.
Not all AWS welding codes have prequalified welding procedures. For instance, the aluminum welding code does not have prequalified welding procedures. So, the fabricator must qualify the welding procedures by testing them. The cost of qualifying a WPS can be considerable by the time one considers the cost of lost production, labor, machining, testing, etc.
However, the lessons learned can be well worth the time, effort, and cost involved.
Even if you're using prequalified procedures, you still have to qualify welders under those procedures. Fewer, less stringent tests, but the tests are still required, are they not?
