Welding Procedure Qualification Test (PQT) Witnessing Guide

A welding procedure qualification test (PQT) is the single event that determines whether a Welding Procedure Specification (WPS) can ever be used in production. Everything that happens on the day of the test — the material verified, the essential variables recorded, the specimens cut and tested — becomes the permanent basis of the Procedure Qualification Record (PQR). If the witnessing is weak, the PQR is weak, and every production weld made against that WPS inherits the gap. This guide sets out exactly what an inspector, whether an ASME Authorised Inspector, a Third Party Inspection (TPI) engineer, or an in-house QA/QC witness, should check before, during, and after a PQT.

This is written primarily around ASME Section IX requirements, since that is the qualification basis most commonly encountered on pressure vessel, piping, and boiler fabrication contracts, with reference points to AWS D1.1 structural practice where the two diverge. Whether you are new to inspection duties or refreshing a checklist before a client audit, the sequence below reflects how a disciplined witness actually works through a qualification test on the shop floor.

Why Witnessing Matters More Than the Paperwork

A signed PQR is only as trustworthy as the person who watched it happen. Fabricators are not being dishonest when a PQR is later found deficient — more often, a variable was recorded from memory after the fact, a thermocouple was not actually reading interpass temperature at the moment it mattered, or a coupon was re-ground and re-numbered between welding and testing without anyone independent present to confirm traceability. Independent witnessing closes exactly these gaps, and it is the reason codes like ASME Section IX give the Authorised Inspector standing to observe the test coupon being welded and tested, per ASME Section IX qualification requirements.

Step 1: Document Review Before the Arc Is Struck

Witnessing does not begin when the welder picks up the torch. It begins in the office, checking that everything the fabricator intends to weld and test actually matches what has been proposed. Skipping this step is the single most common reason a PQT has to be repeated.

Documents to Request in Advance

• The draft or preliminary WPS listing the proposed essential, supplementary essential (if impact testing applies), and nonessential variables.
• Material Test Reports (MTRs) for the base metal coupon, confirming P-Number and Group Number classification.
• Filler metal certificates confirming F-Number, A-Number, and classification, cross-checked against consumable nomenclature.
• Calibration certificates for the welding machine ammeter/voltmeter, and for any thermocouples, contact pyrometers, or preheat monitoring equipment.
• The qualification test plan (QTP), listing which specimens will be cut, in what sequence, and against which acceptance table.
• Confirmation of coupon size against the code figure (ASME IX QW-462 series, or AWS D1.5 figures for bridge work).

Confirming the Essential Variables Before Welding

Every process has its own essential variable table in QW-250. Reviewing these before welding starts, rather than after, lets the inspector flag a problem while it is still cheap to fix. A short pre-weld check should cover:

Step 2: Coupon Setup and Traceability Checks

Once the paperwork is in order, the inspector’s role shifts to the shop floor. Traceability is the theme of this stage: confirming that the piece of metal in front of you is the same piece described in the MTR, and that it will remain identifiable all the way through to the finished PQR.

• Confirm coupon dimensions against the applicable code figure, with enough extra length to allow discard ends plus all planned specimens.
• Verify joint preparation: groove angle, root gap, root face, and backing (if any) match the WPS being qualified.
• Check that joint type and design is representative of the intended production joint, since a fillet-only qualification will not support groove welds.
• Confirm the welding position being used for the test and that it is recorded correctly, since position governs which production positions the resulting WPS can qualify.
• Note ambient conditions if wind or moisture shielding is a concern for the process being tested (this matters particularly for FCAW-S and SMAW in open shop conditions).

Step 3: Witnessing the Welding Itself

During welding, the inspector’s job is continuous observation of the variables that were confirmed in Step 1, not just a single glance at the start. Parameters can and do drift over a multi-pass weld, and a PQR is only valid for the range actually used during the test.

What to Record Pass by Pass

• Amperage and voltage for each pass, read directly from calibrated meters rather than the welder’s estimate.
• Travel speed, either timed directly or calculated from pass length and time.
• Interpass temperature immediately before starting each subsequent pass, taken at the correct location per the WPS (commonly measured 50 mm or 3 in from the weld toe, code-dependent).
• Interpass cleaning method observed between passes (wire brush, grinding) and whether it matches the WPS.
• Number of passes and layers, and whether stringer or weave technique was used if that is an essential variable for the process.

Step 4: Visual Inspection and NDE Before Mechanical Testing

Before any specimen is cut, the completed coupon should pass visual inspection, and radiographic or ultrasonic examination where the code or QTP calls for it. This step exists to screen out gross defects before investing in mechanical testing that would be invalidated by an underlying flaw anyway.

Step 5: Witnessing Specimen Extraction and Mechanical Testing

This is the stage most often under-witnessed, because inspectors sometimes assume that once welding is complete, their job is finished. In practice, specimen extraction and testing introduce their own sources of error, and an inspector who leaves before this stage cannot vouch for the numbers that ultimately appear on the PQR.

Specimen Extraction

• Confirm specimen locations match the code figure and the QTP, not an arbitrary cutting plan.
• Verify machining removes weld reinforcement correctly for tensile and bend specimens per the applicable dimension tables.
• For impact testing, confirm notch location and orientation relative to the weld centreline and fusion line, since a mis-located notch invalidates the result even if the number looks acceptable.
• Check specimen identification is transferred and maintained through machining, so each result can be traced back to its exact coupon location.

Mechanical Testing

Step 6: Reviewing Results and Signing Off the PQR

Once test results are in hand, the inspector’s final task is to check that the recorded essential variables on the draft PQR match what was actually observed, not what was originally planned. Any variable that drifted outside the qualified range during welding — for instance, an interpass temperature excursion — needs to be reflected honestly on the PQR, even if it makes the record less tidy than it would otherwise be.

• Cross-check every essential variable box on the PQR against your own witnessing notes, not the fabricator’s summary alone.
• Confirm supplementary essential variables are included if the WPS will be used where impact testing is mandatory.
• Verify the PQR carries the correct coupon identification, welder identification, date, and your own signature or stamp as witness.
• Retain your own independent notes and photographs; these are often the only defence if a PQR is challenged during a later audit.

PQT Witnessing: ASME IX vs AWS D1.1 at a Glance

Common Non-Conformances Found During PQT Witnessing

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