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ASME Section IX QW-141 Mechanical Tests for Groove Weld PQR

Tension tests, guided bend tests, and when CVN testing is required for ASME Section IX groove weld procedure qualification — what each test verifies and common failure analysis.

ASME IXPQRQW-141mechanical testinggroove weldtension testguided bend

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Every welder qualification and procedure qualification in pressure vessel, piping, and process plant fabrication runs through ASME Section IX. The Welding Procedure Specification (WPS) tells the welder how to weld; the Procedure Qualification Record (PQR) proves through mechanical testing that those parameters produce sound weld metal. For groove welds, the mechanical test suite is defined in QW-141 — and knowing exactly what those tests require and what constitutes a passing result is essential knowledge for any QC engineer or CWI working under an ASME code.

Overview of QW-141 Mechanical Tests

QW-141 specifies the tests required for procedure qualification of groove welds. The core test suite consists of:

  1. Tension tests (QW-150) — two specimens per PQR coupon
  2. Guided bend tests (QW-160) — four specimens per PQR coupon
  3. Notch toughness tests (QW-170) — only when required by the applicable Code section

Additional tests — fillet weld tests (QW-180) and special process tests — apply to specific configurations but are outside the scope of this article, which focuses on standard groove weld PQR qualification.

Compare this to AWS D1.1:2025, which requires tensile tests, bend tests, and macro examination for groove weld PQR — see D1.1 vs. ASME Section IX for the side-by-side comparison.

Tension Tests: QW-150

Specimen Configuration

Two reduced-section tension specimens are cut from the PQR test coupon transverse to the weld. The specimens bridge the weld and are machined to the shape specified in QW-462.1. The weld reinforcement is machined flush with the base metal surface before testing.

Acceptance Criteria

The tensile strength of each specimen must meet or exceed the minimum specified tensile strength of the base metal (or the lower of the two base metals for dissimilar metal joints). This is the only numerical criterion — actual tensile strength values from the mill certification do not factor in; only the code-minimum for the material specification applies.

Two outcomes are acceptable:

  • Failure in the base metal at or above the minimum
  • Failure in the weld metal at or above the minimum

One outcome is NOT acceptable:

  • Failure at any location below the minimum tensile strength, regardless of where the fracture occurs

If the specimen breaks below the required value in the base metal (a heat-affected-zone or base metal failure at understrength), the PQR fails. This catches cases where the preheat, interpass temperature, or heat input degraded the HAZ below the base metal minimum.

Common Failures

Fusion line failure. The fracture runs along the weld-to-base-metal interface, indicating incomplete fusion or a steep hardness gradient. Often accompanied by evidence of cold laps or HAZ brittleness on the fracture face.

HAZ failure at sub-minimum strength. Thermal cycle from welding can overage or soften certain high-strength or heat-treated base metals. Heat-input control on the WPS is the mitigation.

Under-minimum weld metal. Incorrect filler metal classification, dilution from high-chrome or high-alloy base metal, or excessive inter-pass temperature can drive weld metal tensile below the required minimum.

Guided Bend Tests: QW-160

Face Bends, Root Bends, and Side Bends

Guided bend tests bend the specimen over a mandrel to a specified radius to confirm ductility and freedom from fusion or ductility defects. ASME IX specifies three types:

Face bend. The face (cap) of the weld is in tension during bending — the outer surface of the bend. Face bends sample the quality of the cap passes.

Root bend. The root of the weld is in tension. Root bends sample the quality of the root pass and reveal any incomplete penetration, cold lap, or root concavity.

Side bend. The specimen is oriented so that the cross section of the weld (the full thickness) is in tension on the outer face of the bend. Side bends sample the entire weld thickness equally and are the most reliable indicator of internal fusion defects.

Which Bend Type Applies?

The governing rule from ASME IX:

  • Material less than 3/8 in (10 mm) thick: two face bends + two root bends (four total)
  • Material 3/8 in (10 mm) or thicker: four side bends

Side bends are required for thick material because a face or root bend on a 1-in plate develops an enormous bending moment that can fracture sound welds due to insufficient ductility in the specimen geometry — the test would be invalid, not the weld. See ASME Section IX QW-451 thickness and position ranges for how the test coupon thickness selection affects the qualified production range.

Acceptance Criteria

After bending, the specimen surface is examined for cracks or other open defects. The acceptance criterion:

  • No open defects exceeding 1/8 in (3 mm) in any direction on the convex surface of the specimen
  • Cracks at the corners of the specimen that occur during bending are not counted unless associated with slag inclusions or other internal defects

A specimen that cracks completely through is an automatic rejection, even if the individual open defect lengths are under 1/8 in.

Common Failures

Root crack. A complete-penetration groove weld that failed to fuse the root pass properly will open as a root crack in the root bend test. This is the most common guided bend failure and is typically caused by insufficient root pass size, inadequate root opening, or excessive travel speed.

Fusion line crack. A crack propagating along the weld-to-base-metal interface indicates incomplete fusion, often from improper electrode angle or voltage too low for the material thickness.

Slag-inclusion crack. A slag stringer from inadequate inter-pass cleaning becomes a stress concentration during bending and initiates a crack. These appear as linear defects originating from a visible inclusion on the fracture face.

Excessive internal porosity. Distributed gas porosity close to the weld surface can connect under the bending stress and form an open defect exceeding 1/8 in.

Notch Toughness Tests: QW-170

When Required

QW-170 notch toughness (Charpy V-notch, or CVN) tests are not part of the standard PQR test suite. They become required when:

  • The applicable Code section (ASME VIII Div. 1, VIII Div. 2, ASME B31.3, B31.1, or others) specifically requires impact testing for the service condition
  • The base metal specification requires CVN testing as part of its own certification
  • Low-temperature service conditions invoke the impact test provisions of the governing Code

When notch toughness is required, CVN testing becomes a supplementary essential variable under ASME IX — changes to essential variables such as preheat, heat input, base metal P-number, or filler metal F-number can require re-testing of the CVN specimens, not just re-qualification of the mechanical test suite. See ASME Section IX impact test requirements (QW-170) for the full CVN qualification logic.

Test Temperature and Acceptance Value

The CVN test temperature and minimum absorbed energy value are set by the applicable Code section — ASME IX does not specify them independently. Typical provisions for pressure vessels require testing at the minimum design metal temperature (MDMT) or lower, with minimum absorbed energy values specified by material group.

Specimen Extraction and Identification

Cutting Plan

The test coupon is cut by saw or machine torch (not arc gouging, which would introduce heat) into individual specimens in the locations and orientations specified by QW-463. The standard sequence for a flat-position groove weld coupon: tension specimens from the center of the coupon, bend specimens on either side. Mark each specimen with the PQR number and specimen identifier before testing.

Chain of Custody

ASME Section IX requires that the PQR document the test laboratory and test results. The laboratory test report — with specimen dimensions, measured tensile strength, fracture location, and bend specimen photos or results — must be attached to or referenced by the PQR. The PQR is the permanent record; the test report supports it. See reading a PQR test report for how to evaluate what the laboratory report is telling you.

Witness Requirements

ASME IX does not require an Authorized Inspector (AI) to witness PQR testing as a code requirement. The owner's QA program or contract documents may impose witness requirements — and some Owner-User Code jurisdictions require AI involvement at coupon preparation. Confirm the project-specific QA requirements before the testing date.

Connecting QW-141 Results to the WPS Qualified Range

The PQR test results establish what production welding parameters are qualified. The critical link is QW-451, which maps test coupon thickness to production thickness range. A PQR tested on a 1-in coupon in groove weld configuration qualifies production welds from the minimum down to the base metal minimum and up to 2× the coupon thickness for most P-number groups.

Changes to essential variables after PQR qualification — filler metal F-number, base metal P-number, position, or heat input — require a new PQR or amendment. See ASME Section IX WPS documentation requirements (QW-200) for how essential variable changes flow from the PQR to the WPS.

For managing ASME IX PQR records, tracking qualified ranges, and generating WPS documentation without spreadsheet errors, see wpswelding.com/pricing for tools built around the ASME IX qualification structure.

Summary

QW-141 mechanical tests for ASME Section IX groove weld PQR consist of:

  1. Two tension tests — must fail at or above minimum specified tensile strength of the base metal, at any location
  2. Four guided bend tests — face and root bends for material under 3/8 in; side bends for 3/8 in and thicker; no open defects over 1/8 in on the convex surface
  3. CVN tests only when required by the applicable Code section as a supplementary essential variable condition

Knowing the acceptance criteria before the test coupon is cut — and understanding what each failure mode indicates about the welding parameters — is the difference between a PQR that qualifies cleanly and one that requires re-welding and re-testing.

FAQ

Frequently asked.

What mechanical tests are required to qualify a groove weld PQR under ASME Section IX?
At minimum: two reduced-section tension tests and four guided bend tests (two face bends and two root bends for thin material, or four side bends for material 3/8 in and thicker). Some applicable Code sections impose additional CVN impact testing as a supplementary essential variable.
When can side bends substitute for face and root bends in ASME IX?
AWS D1.1 and ASME IX both allow side bends for material 3/8 in (10 mm) or greater in thickness. Side bends are preferred for thick plate because they sample the weld cross-section more evenly than face or root bends.
What is the tension test acceptance criterion in ASME Section IX?
The specimen must fail at or above the minimum tensile strength of the base metal or the lower of the two base metals when dissimilar metals are joined. Failure in the weld metal is acceptable only if the fracture strength still meets or exceeds this minimum.
Does ASME Section IX require CVN (Charpy) tests on every PQR?
No. Notch toughness tests are supplementary essential variables under ASME IX. They are only required when the applicable Code section (ASME VIII Division 1, B31.3, B31.1, etc.) specifically invokes QW-170 notch toughness requirements for the service condition.

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