How to Read a Welding Procedure Specification (WPS)
Key takeaways
- A WPS is the instruction sheet for a specific welded joint; a WPQR is the test evidence that qualified it.
- The two different standards to look for are ISO 15609-1 (how the WPS is written) and ISO 15614-1 (how the procedure is tested).
- A pWPS is preliminary — written before supporting test evidence exists, pending qualification.
- Ask for the WPS number, revision, applicable thickness range and the supporting qualification record.
Three documents that get confused
A lot of sourcing conversations go sideways because both sides use the word "WPS" for three different things. Once you can tell them apart, one question tells you most of what you need to know about a supplier's welding discipline.
| Document | What it is | What it proves |
|---|---|---|
| WPS Welding Procedure Specification | Work instruction for one joint family: process, consumables, groove, parameters, preheat, sequence, inspection | Someone has thought about this joint and written it down |
| pWPS Preliminary WPS | Same document issued before procedure testing | Intent and method, not yet backed by test results |
| WPQR Welding Procedure Qualification Record | Record of the test coupon welded and tested to qualify the procedure | The combination of parameters actually produces acceptable joints |
The relevant standard numbers: ISO 15609-1 governs how a welding procedure specification is written; ISO 15614-1 governs the procedure qualification test for steels. ISO 15607 sets out the general principles that tie them together. If you see all three referenced, the person who wrote the document knew what they were doing.
What a good WPS actually contains
Reading one through, these are the sections that matter, and what each tells you:
- Scope — which product and which joints it covers, and importantly what it excludes. Boundaries are a sign of honesty, not weakness.
- Referenced standards — the framework. Eight to fourteen references is normal for a steel procedure.
- Process and consumables — the process number (135 for MAG), wire standard, shielding gas designation. Specific and checkable.
- Joint design and grooves — including fit-up tolerance. Look for a stated misalignment limit and an explicit ban on packing oversized root gaps.
- Parameters — grouped by application rather than one magic number, with allowance for position and thickness. Watch for the requirement to record actual values at the machine.
- Preheat and interpass — separated by material and thickness, not a single blanket figure.
- Sequence and distortion control — the order welds are made, and whether there is a stated stop-and-correct threshold.
- Inspection and acceptance — which joints get which method, to which quality level.
Our own example
Our document for the 8075W standard bucket (PGI-WPS-8075W-IS, rev. 0, October 2026) is issued as a preliminary WPS covering process 135 MAG, wire to ISO 14341, M21 shielding gas to ISO 14175, plate from 8 to 30 mm, positions PA and PB. It is written to ISO 15609-1 with acceptance levels referencing ISO 5817 quality level C and inspection to ISO 17637 and ISO 9934-1. Its status is stated openly on the cover sheet: formal qualification to ISO 15614-1 is to follow, at which point it becomes a qualified WPS.
We would rather show you a document with "preliminary" on it than claim evidence we do not yet have.
SPEC BOX
| Field | Value |
|---|---|
| Document No. | PGI-WPS-8075W-IS |
| Revision | Rev.0 (2026-10) |
| Status | pWPS — pending qualification |
| Prepared to | ISO 15609-1:2019 |
| Qualification standard | ISO 15614-1:2017 |
| Supporting record | PGI-PQR-135-001 (pending) |
| Coverage | 8–30 mm, PA / PB |
FAQ
Should I care whether it is a pWPS or a fully qualified WPS? If you are ordering standard attachments for general duty — mainly not; the practical controls are the same. If you are supplying into a certified structure or a regulated project, then yes, ask for the WPQR and check the coverage range.
What acceptance level should I specify? See our note on ISO 5817 levels. Internally we default to quality level C with additional restrictions on load-bearing welds.
Can we ask for our own standards instead? Yes. If you work to EN or GB rather than ISO, we can reference the corresponding standard — see our cross-reference note.
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