AWS D1.1:2025 lays out a clear list of required PQR tests for structural weld qualification: tensile specimens, bend specimens, and macro examination. Hardness testing is not on that list — not because the standard considers it unimportant, but because most structural carbon steel welds don't require it for basic qualification. When hardness does appear in a contract spec, many CWIs and QC managers are unsure what they're looking at. This article explains when hardness testing applies, how measurements are taken, and what your PQR documentation needs to show.
What D1.1 actually requires in the PQR
AWS D1.1:2025 Clause 6 governs procedure qualification. The mechanical tests required for a standard PQR on carbon and low-alloy structural steel are:
- Tensile tests — transverse face-break or all-weld-metal tensile, depending on the joint type
- Bend tests — root bend, face bend, or side bend (side bends required when thickness exceeds a threshold)
- Macro examination — cross-sectioned coupon etched to reveal fusion, penetration, and any discontinuities
That's the baseline. Hardness appears in D1.1 only as an optional test that the Engineer of Record (EOR) or contract can invoke. It is never independently required by the standard for ordinary structural carbon steel work.
Rule library based on AWS D1.1:2025; verify against your governing edition.
When contract documents add hardness requirements
Several scenarios trigger hardness testing in structural fabrication:
High-strength quenched-and-tempered steels (A514, A517). The HAZ of these steels is the most vulnerable location for hydrogen-assisted cracking. Elevated hardness in the HAZ — above roughly 350 HV — indicates a martensitic microstructure that has not adequately tempered. Contract specs for A514 frequently require Vickers hardness traverses on the PQR coupon to confirm the preheat and heat-input envelope was adequate.
Weathering steel (A588, A709 Grade 50W). The alloy additions in weathering steel can push HAZ hardness higher than equivalent-strength plain carbon grades. Some bridge and architectural contract specs include a HAZ hardness check.
Post-weld heat treatment (PWHT) verification. When PWHT is specified, contracts sometimes include hardness testing before and after to confirm the heat treatment softened any hard HAZ regions as intended. A meaningful drop in hardness post-PWHT is expected; failure to see that drop can indicate the PWHT cycle was insufficient.
Sour-service proximity. Although NACE/AMPP MR0175 governs sour-service piping rather than structural work, some fabricators who serve both markets apply a 22 HRC (approximately 250 HV) limit across the board. This is a company or contract choice, not a D1.1 requirement.
Dispute resolution and failure investigation. When a weld defect or cracking event occurs in the field, hardness traverses on representative samples are a standard part of root-cause investigation. PQR-level hardness data provides a baseline for comparison.
Hardness scales used in weld evaluation
Three scales appear in weld documentation. Understanding the differences matters when reviewing a contract requirement or interpreting test reports.
Vickers (HV or HV10). The preferred scale for weld HAZ evaluation. The HV10 test uses a 10 kgf (98 N) pyramidal diamond indenter. The indent is small enough — typically 0.3–0.5 mm diagonal — to place measurements accurately within the HAZ at 1 mm intervals from the fusion line. The Vickers scale has no upper limit, making it usable from soft base metal through very hard as-welded martensite.
Brinell (HB). Used for bulk base-metal hardness checks and for verifying general plate condition on receipt of material. The Brinell indent is far larger than Vickers; a 10 mm ball at 3000 kgf leaves a ~4–5 mm impression. This is not suitable for mapping fine HAZ variation.
Rockwell (HRC or HRB). Common in production environments for quick checks on surfaces. Rockwell is less suited for precise HAZ mapping but serviceable for verifying general weld-metal hardness or checking that PWHT softening occurred. Conversion between HRC and HV is approximate — ASTM E140 provides the conversion tables.
When a contract says "hardness not to exceed 350 HV10 in the HAZ," that is a Vickers 10 kgf requirement. Do not substitute Rockwell readings without checking whether the contract allows conversions; some specs explicitly require the Vickers scale.
How to document hardness in the PQR
If your contract requires hardness testing on the PQR coupon, the test report needs to capture:
- Scale and load — HV10, HV5, HRC, etc.
- Traverse location — a sketch showing the cross-section with numbered measurement points
- Individual readings at each point — not just the maximum
- Acceptance criteria — the limit specified in the contract
- Pass/fail determination — explicitly stated, not implied
- Test date and technician or lab identification
The macro photograph (a D1.1 standard deliverable) should accompany the hardness data so reviewers can correlate measurement locations to the visible fusion zone and HAZ.
A PQR coupon should be retained — D1.1 specifies record retention requirements — and some contracts specify retention of the actual test specimens. If the contract is silent on specimens, retain the coupon until all work under that WPS is complete and the audit period has passed.
HAZ hardness and hydrogen cracking: the connection CWIs need to know
The reason hardness matters in structural fabrication is hydrogen-assisted cracking (HAC), also called cold cracking or HACC. The HAZ of carbon and low-alloy steels is where hydrogen, hardness (microstructure), and tensile stress intersect. A martensitic HAZ above roughly 350 HV is considerably more susceptible to hydrogen cracking than a tempered structure below that threshold.
This is why preheat requirements — established partly on the basis of carbon equivalent (CE) calculations — are critical for high-strength and high-CE steels. A properly designed and documented WPS, with preheat held to the minimum specified and heat input kept within the qualified range, should produce a HAZ that stays below the hardness threshold. The PQR hardness test is the confirmation that the qualified procedure actually achieves that.
If PQR hardness readings come back high, the corrective path is usually to increase preheat, tighten interpass temperature control, or adjust heat input — then re-test. It is not acceptable to simply delete the hardness column from the report.
Connecting hardness to the WPS and Table 6.6
When a PQR includes hardness testing, any change to WPS variables that could alter thermal cycle — heat input, preheat, interpass temperature — can affect HAZ hardness. Under AWS D1.1:2025 Table 6.6, heat input change (via travel speed, amperage, or voltage) and preheat or interpass temperature change are already essential variables that trigger requalification. If the original PQR included hardness data, a requalified PQR should include hardness data too.
Document this explicitly in your WPS: if the procedure was qualified with hardness testing, note the hardness limit and reference the PQR test results. An auditor reviewing the WPS package should be able to trace from the hardness requirement in the contract → to the WPS notation → to the PQR test report without hunting through separate files.
For shops managing multiple PQRs and WPSs, software that links the WPS to the supporting PQR records — including any supplemental tests like hardness — reduces the chance of a documentation gap at audit time. See how to read a PQR test report and how multiple PQRs support a single WPS for related context. If your team is still managing this in spreadsheets, the cost comparison between spreadsheets and dedicated WPS software is worth reviewing.
Ready to keep your PQR records organized and audit-ready? See what WPS Welding's qualification tracking covers.