pWPS: the preliminary welding procedure specification

A pWPS looks like a finished specification and carries exactly the same fields. One thing separates them: nobody has yet checked whether the parameters written in it produce a weld that meets the requirements. It is a proposal, not proof.

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Short answer

A pWPS (preliminary Welding Procedure Specification) is a draft procedure. The welding engineer sets out the process, the material, the joint preparation, the current settings, the gas, the preheat and the run sequence — everything that will appear in the finished WPS. A coupon is then welded to the pWPS, the coupon is tested, and if it passes, a WPQR is issued and the specification becomes a full WPS.

The three documents in one sentence: the pWPS proposes, the WPQR proves, the WPS governs.

Where its numbers come from

A pWPS is not guesswork — every field has a source. This part of the job is what separates a welding engineer from an operator:

The more carefully the pWPS is worked out, the better the odds that the coupon passes first time. A failed procedure test costs material, laboratory work and weeks of calendar time, so this is not the stage to economise on.

What happens to it next

The usual route runs like this:

1. the engineer draws up the pWPS;
2. a test coupon is welded to it, witnessed by an examining body or an inspector;
3. the coupon goes through non-destructive and destructive testing;
4. the results are written into the WPQR;
5. the production WPS is issued on the back of it.

A procedure test to EN ISO 15614 is the commonest route, not the only one. EN ISO 15607 also allows qualification based on tested welding consumables (15610), on previous welding experience (15611), on a standard welding procedure (15612) and on a pre-production welding test (15613). The manufacturer picks the route, but the customer and the product standard decide which routes are admissible in a given case.

Why production must not be welded to it

Because nothing backs it. The parameters in it may well be right — and usually are — but nobody has checked them with a tensile, bend and impact test. A weld made to it may meet the requirements, yet no document shows that, and on work under EN 1090 or the pressure equipment directive the absence of that document is the same thing as non-conformity.

The only welding a pWPS covers is the procedure test coupon and the pre-production test to EN ISO 15613, where instead of a separate coupon a piece representing the real structure is tested.

Who draws it up

The manufacturer's welding supervisor — the welding coordinator to EN ISO 14731. The level of technical knowledge required (IWE, IWT, IWS) follows the quality level claimed under EN ISO 3834: comprehensive requirements call for an engineer, elementary ones allow a lower level.

It is the same person who is later answerable for production actually following the qualified procedure — and that is the real reason a pWPS is signed by a named individual rather than by "the technical department".

Author: SpawBaza Updated: 24 August 2026