WPS, PQR and Welder Qualification: The Three Documents Behind Every Sound Weld

Three documents sit behind every structural weld that will survive inspection. They are routinely confused, and the confusion is expensive, because a weld made outside qualified parameters is not a weld with a minor paperwork problem — it is an unqualified weld, and the usual remedy is to cut it out.

The WPS: the instruction

A Welding Procedure Specification is the written instruction given to the welder. It states, at minimum:

• The welding process — SMAW, GMAW, FCAW, GTAW, SAW.
• Parent material group and thickness range.
• Joint design and preparation, including root gap and included angle.
• Consumable classification, diameter and any baking requirement.
• Welding position.
• Current, voltage, travel speed and polarity — the ranges, not single values.
• Preheat and interpass temperature, and any post-weld heat treatment.
• Shielding gas composition and flow rate, where applicable.
• Number and sequence of passes.

A WPS is not a general document. It is qualified for a range, and welding outside that range voids it.

The PQR: the evidence

A Procedure Qualification Record is the test that proves the WPS produces sound metal. A coupon is welded under the proposed parameters, the actual values used are recorded, and the coupon is then destructively tested — typically tensile tests, bend tests, and impact (Charpy) testing where toughness matters, plus macro examination and hardness surveys depending on the code.

The PQR records what was done and what the tests returned. The WPS states what shall be done. Every WPS must be traceable to at least one supporting PQR.

Essential variables — where qualification quietly breaks

Codes define essential variables: parameters that, if changed beyond defined limits, require requalification. Change a non-essential variable and you revise the WPS. Change an essential variable and the qualification is void.

Common examples include a change of welding process, a change in parent material group, moving outside the qualified thickness range, a change in consumable classification, dropping preheat below the qualified minimum, or — where toughness is specified — a change in heat input beyond qualified limits.

This is why "we have a WPS for that" deserves a follow-up question. A WPS qualified on 12 mm plate does not automatically cover 40 mm. A procedure qualified without impact testing does not cover a low-temperature service application.

Welder qualification: the person

The third document certifies that a specific welder can deposit sound metal following a qualified procedure. A Welder Qualification Test Certificate (WQT) is issued against a test coupon, usually examined by radiography or bend testing, and it carries its own ranges of approval:

• Process.
• Material group.
• Thickness range qualified — typically derived from the coupon thickness.
• Diameter range, for pipe.
• Position qualified — and note that a welder qualified in 3G does not automatically cover 6G.
• Joint type: with or without backing, single or double sided.

Continuity matters. Welder qualifications typically require confirmation that the welder has worked in the process within a defined period — commonly six months. A certificate from three years ago, with no continuity record behind it, is not current. Ask for the continuity log, not just the certificate.

How to verify a welding pack in fifteen minutes

1. Take the WPS. Find its PQR reference. Confirm the PQR exists and is attached.
2. Compare the WPS ranges against the PQR actuals — the ranges must derive from the tested values, not exceed them arbitrarily.
3. Check the PQR test results against the acceptance criteria in the governing code.
4. Take the joint you care about. Confirm its thickness, material and position fall inside the WPS ranges.
5. Take the welder register. Confirm the welders assigned to that joint are qualified for that process, position and thickness — and are in continuity.

Five steps. Most welding problems on site are traceable to a break in one of them.

Where this connects to inspection

Qualified procedures and qualified welders reduce the defect rate. They do not eliminate it, which is why non-destructive testing exists. Our companion guide covers choosing between MPI, UT, PT and RT, and when each is the right instrument.

Al Saqr Al Ahmar maintains qualified welding procedures and a current welder qualification register across structural steel, pipeline and stainless steel work from our Musaffah yard. See our capabilities or send us a scope.