WPS vs PQR: What's the Difference and Why Both Matter

If you've worked in fabrication, engineering procurement, or construction, you've encountered WPS and PQR as a pair, often submitted together, often reviewed together, and often confused with each other. They serve different purposes and satisfy different compliance requirements. Understanding the difference matters whether you're a fabricator, an EPC contractor reviewing vendor documentation, or an owner-operator qualifying a new welding subcontractor.

This guide explains what each document is, what it must contain, how they relate, and why a deficient WPS or PQR can stop a project.

What Is a WPS?

A Welding Procedure Specification (WPS) is the written document that tells welders how to execute a specific weld. It specifies all the variables that affect weld quality: the base materials, filler metals, preheat requirements, interpass temperature limits, joint design, position, heat input range, post-weld heat treatment (PWHT) requirements, and more.

Think of the WPS as the instruction sheet. A welder performing a butt weld on a P-1 carbon steel pressure vessel in the 2G position should have a WPS in hand that specifies every parameter relevant to that weld. Deviating from the WPS, such as using a different electrode, higher interpass temperature, or different preheat, is a non-conformance.

Under ASME Section IX, the WPS must reference the PQR (or PQRs) that support it. A WPS that isn't supported by test data is not a qualified procedure. It's just a document.

What Is a PQR?

A Procedure Qualification Record (PQR) is the test record that proves a welding procedure produces acceptable results. To create a PQR, a test weld is made using the essential variables of the proposed procedure. Test specimens are then cut from the weld and subjected to mechanical testing: tensile testing, bend testing, notch toughness testing (where required), and sometimes hardness or macroetch examination.

The test results, pass/fail on each specimen, laboratory certifications, and the actual welding data recorded during the test weld, are compiled into the PQR. A manufacturer's or contractor's authorized representative signs the PQR, certifying that the test was performed as described.

Under ASME Section IX, the PQR is the foundation. A single PQR can support multiple WPS documents, provided the WPS variables remain within the qualified ranges established by the test.

WPS vs PQR: Side-by-Side

The Relationship Between WPS and PQR

A WPS must be supported by one or more PQRs. The PQR establishes qualified ranges for the essential variables, including the material P-number, filler metal F-number, heat input range, preheat, PWHT condition, and others. The WPS must stay within those ranges.

For example: if a PQR was tested with a heat input of 45 kJ/in, ASME Section IX establishes qualified limits around that value. A WPS that specifies a heat input outside those limits isn't supported by the PQR and is not a qualified procedure.

This is the most common deficiency found during WPS/PQR review: the WPS specifies ranges or conditions that extend beyond what the supporting PQR actually qualifies. The fix usually requires either revising the WPS to stay within qualified ranges, or conducting additional tests to extend the PQR qualification.

What Standards Govern WPS and PQR?

The applicable standard depends on the type of work and the jurisdiction:

In Alberta, pressure-retaining equipment (vessels, piping, heat exchangers) must comply with the ABSA (Alberta Boilers Safety Association) regulatory framework, which references ASME Section IX for welding qualifications. This means WPS and PQR documents submitted for ABSA-regulated work must meet ASME IX requirements.

What a WPS/PQR Reviewer Checks

When Norman QC performs a remote WPS/PQR review, the review checks the following for each procedure package:

• ▸WPS completeness: All required essential, supplementary essential (where applicable), and nonessential variables are addressed
• ▸PQR-to-WPS traceability: The WPS correctly references the supporting PQR(s), and the PQR number matches
• ▸Variable ranges: WPS ranges fall within the qualified ranges established by the PQR, including base material P-numbers, filler F-numbers, heat input, preheat, PWHT, thickness, and diameter
• ▸Test record completeness: PQR records actual test parameters (not just specified ranges) and includes all required mechanical test results with lab certifications
• ▸Impact testing requirements: Whether notch toughness testing was required and whether the PQR records it
• ▸PWHT consistency: If PWHT is a supplementary essential variable, whether the WPS and PQR are consistent
• ▸Welder qualification applicability: Whether the WPS, when used in production, will support welder qualification requirements
• ▸Signatory authority: Whether the document is signed by an authorized representative as required

The output is a signed PDF review report listing: conforming items, non-conformances, and observations. Non-conformances require resolution before the procedure is used in production. Observations are informational and advisory items that don't require correction but may affect future audits. For scope, turnaround time, and pricing, see the remote WPS/PQR review service page.

Why WPS/PQR Issues Stop Projects

A deficient WPS or PQR discovered mid-project creates real cost and schedule impact. If an inspector or client QC review finds that the welding procedure used for production welds wasn't properly qualified, or that the WPS used conditions outside the PQR's qualified range, the following consequences are possible:

Requalification testing: A new test weld must be made and tested before production welding continues. This takes days and has laboratory turnaround time.

Repair or re-inspection of completed welds: In some cases, welds made under a non-conforming WPS may need NDE re-inspection or even excavation and repair.

Regulatory non-compliance: For ABSA-regulated pressure equipment, a non-qualified welding procedure can prevent Code stamp or registration approval.

Catching WPS/PQR deficiencies before fabrication starts through independent document review is materially cheaper than catching them after production welding is underway. For typical review costs, see our 2026 API inspection pricing guide.

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