AWS B4.0 Mechanical Testing of Welds: PQR Requirements

The Standard Behind the Specimens

Every Procedure Qualification Record (PQR) for AWS D1.1 structural welding ends with mechanical test results. Those tests — tensile, guided bend, Charpy V-notch impact — need to follow a consistent method so that results from one laboratory are comparable to another and to the acceptance criteria written into the code.

AWS B4.0, Standard Methods for Mechanical Testing of Welds, is the normative reference that standardizes those methods. When D1.1:2025 says mechanical tests shall be performed per AWS B4.0, it means specimen geometry, surface finish, testing equipment calibration, and reporting format all come from B4.0 — not from the lab's in-house procedure.

For a CWI supervising a PQR test or a welding engineer reviewing a lab report, B4.0 fluency is essential. A specimen machined to the wrong dimensions or bent on an undersized mandrel invalidates the test, even if the weld itself was sound.

Reduced Section Tensile Test Specimens

The tensile test is used on groove weld PQRs to confirm that the weld metal and HAZ can achieve the minimum UTS requirement — typically matching the base metal minimum UTS for structural steel WPS qualification under D1.1.

AWS B4.0 and D1.1 together specify the reduced section tensile specimen: a flat coupon with a reduced gauge section typically 3/4 inch wide, of sufficient grip length on each end. Thickness equals the full plate thickness up to 1 inch; thicker plates are tested as through-thickness slice specimens.

CWI considerations:

• Surface finish in the gauge section matters. Rough saw cuts can initiate failures at the coupon surface rather than in the weld. The lab should machine, not flame-cut, the reduced section.
• For A514/A517 high-strength steel PQRs, the tensile specimen must fracture at or above the base metal minimum UTS. Fracture in the weld metal below the UTS minimum is a test failure.
• The test report must record fracture location (weld, HAZ, or base metal), ultimate tensile strength, and whether the result met the acceptance criterion. A lab report that says only "pass" without the actual UTS value is deficient documentation.

Guided Bend Tests: Plunger Radius and Acceptance Criteria

The guided bend test evaluates ductility and fusion continuity in the weld zone. A specimen is wrapped over a mandrel (the plunger) to a prescribed bend angle — 180° for most structural steel groove welds — and the tensile surface is then examined for cracks.

AWS B4.0 specifies both the plunger radius and die opening dimensions as a function of base metal yield strength category:

• Steel with yield strength ≤ 50 ksi (A36, A572 Grade 50, A992): standard plunger radius is twice the specimen thickness.
• Higher-strength steel (A572 Grade 65, A514): a larger plunger radius is required. The higher material hardness means the same plunger radius that works for mild steel would cause fracture from material brittleness rather than from a weld defect.

Using the wrong plunger radius for the base metal is one of the most common B4.0 compliance failures found when reviewing PQR lab reports.

Face, root, and side bends:

Bend specimen type depends on base metal thickness:

• Base metal < 3/8 inch: two face bend + two root bend specimens from the test plate.
• Base metal ≥ 3/8 inch: four side bend specimens. Each side bend specimen represents one quarter of the full weld cross section with the entire thickness placed in tension.

Acceptance criteria per AWS D1.1: After bending, no open discontinuity in the weld or HAZ shall exceed 1/8 inch (3 mm) in any direction. Corner cracks up to 1/4 inch (6 mm) are acceptable unless they originate from a visible porosity or slag inclusion — if a corner crack starts at a flaw, it is rejectable regardless of length. Record the crack length and location, and note whether a corner crack is associated with a flaw.

Charpy V-Notch (CVN) Impact Test Specimens

CVN testing is required for PQRs where the production WPS is subject to the supplementary essential variables in AWS D1.1:2025 Table 6.8 — principally when the project specification mandates minimum CVN absorbed energy for the weld metal or HAZ. Demand-critical welds in seismic moment frames are a common trigger.

Rule library based on AWS D1.1:2025; verify against your governing edition.

B4.0 defines the Charpy specimen as 10 mm × 10 mm × 55 mm with a 2 mm V-notch. For structural weld PQRs, specimens are typically oriented transverse to the weld axis (notch cutting into the weld from the face side). Notch positions vary by owner specification but commonly include: weld centerline (WCL), fusion line (FL), FL+2 mm, and FL+5 mm into the HAZ.

Critical reporting requirements:

• Absorbed energy in ft-lbf (or Joules), percent shear area, and lateral expansion for each specimen.
• Report the average of the set and the lowest single value — AWS D1.1 acceptance criteria reference both.
• Test temperature must match the design minimum service temperature or the temperature specified in Table 6.8. A lab that tests at the wrong temperature produces an invalid data set.

Confirm that your lab's ISO 17025 accreditation scope specifically includes Charpy impact testing at the required temperature. Not all labs are equipped for sub-zero CVN work.

Macro Etching: Not in B4.0 But Required by D1.1

AWS D1.1 also requires macro-etch examination of cross-section specimens from the PQR test plate. Macro etching is not a mechanical test but a metallographic examination that reveals weld profile, fusion pattern, HAZ width, root penetration, and any gross discontinuities such as incomplete fusion or cracks.

The most common etchant for structural carbon steel is 2% nital (2 mL nitric acid in 100 mL ethanol) applied to a polished cross-section. The weld cross-section should show complete fusion to the root and all joint faces, with no cracks, lack of fusion, or excessive porosity visible at low magnification (typically 5× or less).

B4.0 is not the governing document for macro preparation. Preparation is done per the lab's procedure referencing AWS A9.4 or an equivalent standard. The CWI or welding engineer reviewing the PQR must verify the macro report includes the etchant used, magnification, and a clear interpretation of whether the weld section is acceptable.

Working With the Test Lab

To avoid invalid test results that require re-welding and retesting:

1. Provide the full test plate drawing to the lab before cutting. Confirm specimen count, locations, notch positions, and bend test type (face/root vs. side) before the lab cuts anything. Retroactive layout changes after cutting often leave insufficient material for mandatory retests.

2. Confirm the lab uses the current B4.0 edition. The normative reference in D1.1:2025 should align with the edition the lab's test standard operating procedures reference.

3. Request a pre-test review meeting for high-stakes PQRs. For A514 base metal, CVN requirements, or demand-critical welds, a 30-minute call before any tests run prevents specimen geometry errors that cost weeks to correct.

4. Check accreditation scope in detail. An A2LA or ISO 17025-accredited lab is required by many AISC clients. Confirm that the accreditation scope lists welding mechanical testing specifically — tensile, bend, and CVN at the required temperature range. A lab with general metallurgical accreditation may not be in scope for Charpy at −20°F.

5. Require the lab report to show actual values, not just pass/fail. Auditors reviewing PQR packages years after qualification will want to see the tensile UTS in psi, the CVN energy in ft-lbf at the specified temperature, and the bend crack lengths. Pass/fail notation without data is not an adequate PQR record.

Nick-Break and Macro — The Overlooked Tests

For fillet weld and partial joint penetration groove weld PQRs under certain D1.1 qualification paths, a nick-break test is required rather than a tensile specimen. The nick-break test splits a fillet weld specimen along the weld axis after notching, and the fracture surface is examined for porosity, lack of fusion, and slag inclusions. B4.0 defines the specimen geometry and notch depth.

Including nick-break results in your PQR package alongside the macro is good practice even when not mandated — it documents complete fusion and root condition without the cost of a tensile machine setup.

For further detail on the PQR test sequence, see PQR tensile and bend test requirements under AWS D1.1 and Charpy CVN testing under AWS D1.1 Table 6.8. For selecting and qualifying a test lab, see PQR test laboratory selection.

Storing your PQR mechanical test reports linked to the corresponding WPS — with test date, lab accreditation number, and specimen disposition tracked — is the foundation of an audit-ready welding program. See wpswelding.com/pricing for how the WPS platform manages PQR documentation alongside the procedure itself.