Welding Procedure Qualification (WPQ2)
The qualification chain
A preliminary WPS (pWPS) is written, used to weld a test assembly, and the assembly is tested. If all results meet the standard's acceptance criteria, a Welding Procedure Qualification Record (WPQR/PQR) is issued, and production WPSs are then written within the ranges that record supports. The WPQR is a record, not a usable work instruction - a frequent trap.
Variables
Essential variables: process, base-material group (P-number or ISO 15608 group), thickness, joint design, filler classification, preheat and interpass temperature, heat input, post-weld heat treatment, current type/polarity, position, backing and shielding gas. Change one beyond its permitted range and the procedure needs requalification. Non-essential variables can be changed by revising the WPS. Supplementary essential variables (impact/toughness-related) only bite when notch toughness is specified.
Testing
Typically visual, radiographic or ultrasonic, transverse tensile, bend, macro; plus impact and hardness where specified. Acceptance criteria belong to the standard, not to the customer's preference or the inspector's judgement.
Range of qualification
Ranges are derived from the coupon: thickness (the ISO 15614-1 rule of thumb is about 0.5t to 2t, with minimum and maximum limits), position, material group, and - where impact testing was done - the toughness group. In a multi-process procedure each process is qualified on its own deposited thickness.
Worked example: a 20 mm coupon in a Group 1 carbon steel, single process, supports a rough base-metal range from about 10 mm to 40 mm. But if impact testing was a supplementary essential variable and no impact specimens were tested, that procedure cannot be used for toughness-required service regardless of thickness.
Traps: issuing a WPS straight from a WPQR without translating the ranges; forgetting PWHT and heat-input range are usually essential; assuming another organisation's WPQR is automatically usable without documented acceptance of responsibility.