ASME Section IX QW-200 Series: WPS Variables Explained
Before Article III’s process-specific QW-25X tables tell you which individual variables are essential for SMAW versus GTAW versus SAW, the QW-200 series at the front of Article II lays down the foundational rules: what a Welding Procedure Specification must actually contain, what a Procedure Qualification Record must document, and who is responsible for qualifying a procedure before it can be used. This module is a deep-dive companion to the Article I and Article II modules already in this series, focused specifically on the QW-200 paragraphs that define document content and organizational responsibility.
By the end of this module you should be able to explain the difference in required content between a WPS and a PQR, describe why one qualifies a range while the other documents a single test, and understand the rules around which organization is permitted to rely on which procedure qualification. A timed quiz at the end checks your understanding.
Where this fits: Article I sets welding general requirements. The QW-200 series, covered here, opens Article II by defining what a WPS and PQR must contain and who is responsible for qualifying them. Article III then supplies the detailed variable tables the QW-200 series framework points to for each specific process.
Purpose of the QW-200 Series
The QW-200 series sits at the opening of Article II and answers a deceptively simple question: what exactly has to be written down, and by whom, before a welding procedure can be considered qualified? Everything that follows in Article II’s variable rules and Article III’s process tables assumes the WPS and PQR documents already exist in a properly structured form, and the QW-200 series is what defines that structure.
Two closely related but distinct paragraphs anchor this section: one addressing required WPS content, and one addressing required PQR content. Confusing what belongs on which document is one of the most common documentation errors reviewers encounter, which is exactly why this module treats them as a dedicated deep-dive rather than folding them into the broader Article II discussion.
What a WPS Must Contain
A Welding Procedure Specification is an instructional document: it tells a welder exactly how to make a production weld, expressed as a range of acceptable values for every essential, supplementary essential (where applicable), and nonessential variable relevant to the process. The QW-200 series requires the WPS to address each of the following categories at minimum, with the specific variables drawn from the appropriate QW-25X table in Article III.
| WPS Section | What It Documents |
|---|---|
| Joint Design | Joint type, groove angle, root opening, backing (if any) |
| Base Metals | P-Number/Group Number range, thickness range qualified |
| Filler Metals | F-Number, A-Number (where applicable), classification, diameter range |
| Position | Welding position(s) the procedure is qualified for |
| Preheat | Minimum preheat and maximum interpass temperature |
| Post-Weld Heat Treatment | Temperature range and time, if PWHT is performed |
| Gas | Shielding and backing gas type and flow rate range, where applicable |
| Electrical Characteristics | Current type/polarity, amperage and voltage ranges |
| Technique | String vs weave, multi-pass vs single-pass, cleaning method, peening |
Key point: A WPS expresses every value as a qualified range, not a single fixed number. This is what allows one qualified procedure to cover realistic production variation in material thickness, position, and minor parameter drift without needing a separate qualification for every conceivable combination.
What a PQR Must Contain
The Procedure Qualification Record is the opposite of a WPS in one important respect: rather than documenting a range of acceptable values, it documents the actual, specific values used to weld the one test coupon that proved the procedure works. Where the WPS says “150 to 250 amps,” the PQR says “the test coupon was welded at 210 amps,” because the PQR is a factual record of what actually happened during qualification testing, not an instructional range for future welders.
| PQR Section | What It Documents |
|---|---|
| Actual Variables Used | The specific value of every essential and supplementary essential variable during the test weld |
| Mechanical Test Results | Tensile strength, bend test results, and impact test results (where required) from the actual test coupon |
| Welder Identification | Who welded the test coupon, for traceability, though this does not itself qualify that individual welder under Article IV |
| Certification | A statement certifying the recorded information is accurate, signed by the manufacturer or contractor |
Why the WPS-to-PQR Logic Matters
The relationship between these two documents is the logical core of Article II: the PQR proves, through actual destructive testing of one specific test coupon, that a set of specific values produces a sound weld. The WPS then extrapolates outward from that single proven data point to a defensible range, based on the essential and supplementary essential variable rules in Article III, that production welders can use with confidence the results will remain sound.
This is why essential variables are treated so strictly. Extrapolating too far from the single tested data point, by allowing too wide a range on an essential variable, would undermine the entire logical basis connecting the PQR’s proof to the WPS’s production instructions. Nonessential variables get more latitude precisely because they do not threaten that underlying logical connection.
Manufacturer and Contractor Responsibility
The QW-200 series also establishes a responsibility principle that surprises people new to the code: each manufacturer or contractor is generally responsible for qualifying its own welding procedures, and cannot simply adopt another company’s PQR as the basis for its own WPS, even if the process and materials are identical. This exists because qualification is tied to the actual demonstrated capability of a specific organization’s equipment, personnel, and quality controls, not just to the abstract combination of variables on paper.
There are limited, specifically defined circumstances, generally involving common ownership or direct organizational control between companies, where one entity’s qualification testing can support another’s WPS. Outside those specific conditions, each organization needs its own supporting PQR.
Common misunderstanding: Buying a “pre-qualified” WPS document from a vendor or finding one online does not make it a valid qualified procedure for your organization unless your organization has its own supporting PQR, or you are using a properly adopted Standard Welding Procedure Specification (SWPS) under Article V, which follows its own distinct adoption rules.
Common Documentation Errors
Reviewers and auditors repeatedly encounter the same handful of documentation mistakes tied to the QW-200 series requirements.
- Recording a range on the PQR instead of the actual tested value: the PQR should reflect exactly what was measured during the test weld, not a range copied over from the WPS.
- A WPS range wider than what the supporting PQR and Article III’s variable rules justify: every value on the WPS must be traceable back to what the PQR and the applicable essential variable rules actually support.
- Missing required WPS content categories: omitting a required section, such as technique or post-weld heat treatment details, even when the answer is “not applicable,” rather than explicitly stating that it does not apply.
- Assuming a purchased or borrowed PQR qualifies your organization’s WPS: without meeting the specific conditions allowing shared qualification, each organization needs its own supporting test record.
Practical tip: When reviewing a WPS package, always pull the PQR alongside it and check that every essential variable value on the WPS falls within what the PQR and Article III actually justify. A WPS that looks complete and well-formatted can still be invalid if this underlying traceability is broken.
Practice Quiz: QW-200 Series — WPS Variables Explained
Test your understanding of the QW-200 series with this 10-question timed quiz. You have 20 seconds per question. Your best score is saved automatically so you can track improvement across attempts.
10 questions · 20 seconds per question · Instant feedback after each answer
Next in this series: With the QW-200 series foundation in place, Article III’s detailed QW-25X variable tables will make far more sense, since you now understand exactly what those tables are feeding into on the WPS and PQR documents themselves.