Welding Procedure and Performance Qualification: Variables and Ranges
What to master
Distinguish the procedure qualification record (PQR) from the welding procedure specification (WPS) and the welder performance qualification (WPQ). The PQR records actual test data; the WPS is the production document derived from it; the WPQ demonstrates a welder's or operator's ability. Essential variables must be listed and controlled. In ASME IX these include base metal P-number, filler F-number, thickness, position, preheat, PWHT and essential process details. ISO 15614 uses similar logic but different ranges. Supplementary essential variables apply when notch toughness is required. Know the difference between welder and welding operator qualification, and when a WPS supports multiple processes or positions.
Traps
A frequent mistake is assuming a qualified WPS also qualifies the welder. Another is changing a non-essential variable and failing to revise the WPS, or changing an essential variable and failing to requalify. Thickness ranges are often misapplied: a coupon qualifies a range, not the exact thickness only. Position and progression can be essential. Consumable grouping must be checked rather than assumed. Do not accept a PQR without test records, and do not accept a WPS that cites an unavailable PQR.
Worked example
Under ASME IX QW-451, a groove-weld procedure qualification on 10 mm plate with SMAW generally qualifies base metal from 1.5 mm to 20 mm (2T), subject to the specific clause and impact-testing rules. The same 10 mm coupon does not automatically qualify unlimited thickness. Always read the thickness table for the process and test type, and record both the qualified range and the production thickness on the WPS.