The moment the welding inspector reaches the site, the same acronyms repeat in every conversation: WPS, WPQR, pWPS, PQR. They are not decorative red tape: they define how to weld, prove the procedure works and underpin the traceability of every joint. Without that pack, a run can be rejected even if the bead looks flawless to the naked eye. This guide explains what each document is, who demands it and where dossiers usually fail.
WPS — the technical recipe for each joint
The WPS (Welding Procedure Specification) states how to weld a given joint. A complete WPS pins down, at a minimum:
- Process (111, 135, 136, 141…) and technique (manual, mechanized).
- Materials: parent metal (grouped per ISO/TR 15608), consumable and its classification.
- Joint geometry: preparation, sketch, thickness and diameter range.
- Electrical parameters: current, voltage, current type, travel speed and heat input.
- Shielding gas, flow rate and, where applicable, backing gas (purge).
- Positions, pass sequence, interpass temperature, preheat and post-weld heat treatment (PWHT).
Until the recipe is validated by testing it is called a pWPS (preliminary): a technical proposal, not a guarantee. Welding production against an unbacked pWPS is one of the fastest ways to lose an audit.
WPQR — proof the recipe works
The WPQR (Welding Procedure Qualification Record) is the experimental validation of the pWPS, in Europe to EN ISO 15614-1: a coupon is welded with the proposed parameters and put through non-destructive testing (visual, radiography or ultrasonics, penetrant or magnetic particle) and destructive testing (tensile, bend, impact, macro, hardness). If everything passes, the issued report — the WPQR — backs the WPS within precise qualification ranges: thicknesses, diameters, material groups and positions all derive from what was tested, following the tables of the standard.
A vocabulary note that avoids site arguments: in the ASME world (American code), the equivalent document is called a PQR (Procedure Qualification Record, per ASME IX). It is the same paper with different range rules — but the acronyms are not interchangeable between codes, and a dossier mixing ISO ranges with ASME ranges is a classic non-conformity. If your project straddles both frameworks, see our comparison ISO 9606 vs AWS D1.1.
Who demands this documentation
It depends on the product and the contract, but the big frameworks are:
- EN 1090 — CE-marked structural steelwork: from EXC2 upwards, qualified procedures are mandatory.
- Pressure equipment — the European directive and its supporting standards (EN 13480 for piping, EN 13445 for vessels) require qualified procedures, generally approved by a third party.
- ASME IX — refining and petrochemical projects designed to American code: WPS and PQR under ASME rules.
- The client contract — even with no standard in play, any serious industrial specification (and any ISO 3834 system) demands the full pack.
How it relates to the welder qualification
The WPQR qualifies the procedure; UNE-EN ISO 9606 qualifies the person. They are the two legs of the same stool, and the inspector will demand both: a WPS backed by its WPQR on the table, and welders whose certificate — process, material, thickness, position — falls within the range of that WPS. A brilliant welder on an unbacked WPS does not hold the dossier together; a flawless WPS executed by an out-of-range welder does not either. How to read and verify the welder certificate, field by field, is covered in our guide to the UNE-EN ISO 9606 welder qualification.
A nuance that surprises many buyers: unlike the welder qualification, the WPQR does not expire. Once qualified, the procedure remains valid as long as its essential variables do not change — a new parent material, another consumable or a different thickness range forces requalification. What does expire, every six months, is the qualification of the person executing it: six-month confirmations, revalidations, sick leaves. Which is why, in practice, dossiers fail far more often on the people leg than on the procedure leg — and why the welder × WPS matrix has to be kept alive throughout the project, not just photographed on day one.
Documentation errors that sink audits
- A WPS with no backing WPQR — or backed out of range: production thickness above what was qualified, material from another group, position not covered.
- Production parameters outside the WPS — the weld log says one thing, the actual bead was run with another; heat input is the usual giveaway.
- Welder qualifications that do not match the WPS — a welder qualified in 135 executing a 141 WPS.
- Broken traceability — joints with no record of which WPS was applied and which welder executed them.
- Uncontrolled revisions — WPS revision 3 in the office and revision 1 printed on the scaffold.
- Acronyms swapped between codes — ASME ranges applied to an ISO project, or the other way round.
The buyer checklist
Before production starts, the buyer of welding services should hold:
- A list of applicable WPS for the scope, each referencing its WPQR.
- A welder × WPS matrix: who is qualified to execute what, with validity dates.
- Explicit agreement on the reference code (ISO or ASME) and the inspection level.
- A joint log system: joint, WPS, welder, test, result.
- An identified welding coordinator (the ISO 14731 figure) on the executing side.
- Document revision control on site — only the current version on the scaffold.
At Iron Pulse, the documentation dossier — WPS, WPQR and welder qualifications matched to every joint — is part of the mobilization, not an extra. See our quality and documentation page or talk to the team before the next audit, not after it.
