WPS vs PQR: welding procedure documents explained
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The practical difference between a Welding Procedure Specification and the qualification record behind it, including pWPS, WPQR/PQR and welder qualification.
A Welding Procedure Specification (WPS) tells the production team how a weld is to be made.
A Procedure Qualification Record (PQR)—often called a WPQR in the ISO/EN system—records how a qualification test weld was actually made and what the examination/test results were.
They are related documents, but they are not the same thing.
The basic document chain
For procedure qualification by testing, the logic is broadly:
pWPS → qualification test weld → examination/testing → WPQR/PQR → qualified production WPS
The exact terminology and qualification route depend on the governing code or standard.
ISO 15607 provides the general framework. ISO 15609-1 specifies content requirements for arc-welding WPSs, while ISO 15614-1 covers qualification by welding procedure test for steels and nickel/nickel alloys within its scope.
What is a pWPS?
A preliminary Welding Procedure Specification (pWPS) is the procedure used to make the qualification test weld.
It defines the intended variables before qualification has demonstrated the acceptable range.
If the test is successful, the results support preparation/approval of a production WPS within the range qualified by the applicable standard.
What is in a WPS?
The WPS is the production instruction.
Depending on the process and code, it can include items such as:
- welding process;
- joint type and preparation;
- base material/group;
- thickness and diameter range;
- welding position;
- filler metal;
- shielding gas or flux;
- current type and polarity;
- amperage and voltage ranges;
- travel speed or heat-input controls;
- preheat;
- interpass temperature;
- bead sequence;
- back gouging;
- post-heat;
- PWHT.
The WPS should contain enough information for production welding to remain within the qualified conditions.
What is in the PQR/WPQR?
The qualification record is evidence of what happened during the procedure test.
It normally records:
- actual test-piece materials and dimensions;
- actual welding variables used;
- joint configuration;
- consumables;
- preheat/interpass data;
- heat input or relevant parameters;
- PWHT where applicable;
- visual/NDT results;
- destructive mechanical test results;
- any required hardness, impact or macro/micro examination;
- approvals/signatures required by the qualification system.
The PQR/WPQR is not a set of recommended production ranges in the same sense as a WPS. It is the factual record that supports the qualified range.
One PQR can support more than one WPS
Qualification standards define ranges within which a successful procedure test is valid.
Therefore one WPQR/PQR can sometimes support several WPSs, provided each production WPS stays within the qualified range.
Conversely, a WPS cannot simply cite an unrelated PQR because the welding process or material looks similar. Essential variables and qualified ranges must align.
WPS/PQR is not welder qualification
Another frequent confusion is mixing up the procedure and the person.
- WPS: how the joint is to be welded.
- WPQR/PQR: evidence that the welding procedure has been qualified.
- Welder qualification: evidence that an individual welder is qualified for the applicable range.
- Welding operator qualification: applies to mechanized/automatic welding where relevant.
ISO 9606-1 addresses qualification testing of welders for fusion welding of steels. Other standards apply to welding operators and different materials/processes.
A qualified WPS does not qualify the welder, and a qualified welder does not create a qualified procedure.
What buyers should check
When reviewing a fabrication package, do not stop at "WPS attached".
Check that:
- the governing welding code/qualification standard is identified;
- the WPS references appropriate supporting qualification;
- base-material groups/grades are covered;
- the actual production thickness/diameter is within the range;
- the welding process and consumables match;
- required positions are covered;
- preheat/interpass requirements are consistent;
- heat input restrictions are respected;
- required PWHT is represented by the qualification;
- required impact/hardness tests were included where applicable.
The exact essential variables and ranges must be checked against the governing qualification standard or fabrication code.
PWHT is especially important
If production welding will be followed by PWHT, the qualification package must be reviewed for compatibility with that thermal condition.
A change to PWHT can change weld/HAZ properties and can be an essential qualification variable.
See Post-weld heat treatment (PWHT): when it appears in steel specifications.
WPS and high-strength steels
High-strength Q&T or TMCP steels may have restricted welding windows.
A technically complete WPS can therefore include controls for:
- maximum heat input;
- preheat;
- interpass temperature;
- hydrogen level;
- filler strength;
- cooling;
- repair procedure.
The fact that a welder has previously welded "S690" or "X65" does not by itself demonstrate that the proposed procedure is qualified for the actual product.
Common document-review mistakes
A WPS without its qualification basis
A WPS may look complete while still lacking adequate supporting qualification.
A PQR copied from a different material or thickness
Similarity is not enough; the qualified range must be checked.
Confusing WPQR with WPQ
WPQR relates to the welding procedure. WPQ/WPQ-type terminology is often used for welder/operator performance qualification in other systems.
Ignoring the standard system
ISO/EN and ASME use overlapping but not identical terminology and qualification rules. Do not mechanically translate every term one-for-one.
Treating approval stamps as the technical review
A signature does not replace checking the actual qualified variables.
Procurement takeaway
The easiest way to remember the difference is:
WPS = instruction.
PQR/WPQR = qualification evidence.
Then check separately that the welder/operator is qualified and that all three layers match the actual production weld.
References and verification sources
Standards referenced
- ISO 15607:2019
- ISO 15609-1:2019
- ISO 15614-1:2017
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WPS vs PQR: welding procedure documents explained
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