What does the fillet weld break test actually check?

Breaking the specimen through the weld throat exposes the fused cross-section. The fractured surface reveals internal defects — porosity, slag inclusions, cracks, and incomplete fusion — that visual inspection or surface NDE cannot detect.

Is the fillet break test required for groove weld PQR as well?

No. The fillet break test applies to fillet weld procedure qualification. Groove weld PQR testing under AWS D1.1 uses tension tests and guided bend tests — not a fillet break.

Can a failed fillet break specimen be replaced by re-cutting the same test weld?

No. If the break test fails acceptance criteria, the procedure is not qualified. A new test assembly must be prepared and tested from scratch — you cannot cut additional specimens from the original weld run.

Does a groove weld PQR automatically cover fillet welds?

Under AWS D1.1, qualifying a groove weld procedure extends to fillet welds within the qualified thickness range. However, a procedure qualified solely for fillet weld work (without groove weld test coupons) requires the fillet break test as the primary mechanical test.

Nick-break test in fillet weld PQR qualification: AWS D1.1

AWS D1.1 fillet weld PQR qualification requires a fillet break test. Learn specimen prep, break direction, acceptance criteria, and how to document results on your PQR.

When a fabricator qualifies a welding procedure for fillet weld work under AWS D1.1, the test regimen looks different from a groove weld PQR. There are no tension bars and no guided bends. Instead, the primary mechanical test is the fillet weld break test — sometimes called the nick-break test in shop shorthand — paired with a macro examination. Together these two tests reveal internal soundness and fusion quality that neither visual inspection nor surface NDE can access.

Understanding exactly what the test requires, how to break the specimens, and what the acceptance criteria permit is essential before you schedule a qualification weld. A failed specimen — or a correctly run specimen documented incorrectly on the PQR — can invalidate the entire procedure.

What the break test actually reveals

A fillet weld break test works by forcing a fracture through the weld throat. When the weld separates, the fracture surface exposes the cross-section of the weld metal and the fusion zones. The inspector examines this surface for:

Porosity: gas pockets trapped during solidification. Acceptance criteria set limits on maximum size and distribution.
Slag inclusions: entrapped flux residue, common in SMAW and FCAW-S if interpass cleaning was inadequate.
Incomplete fusion: weld metal that did not fuse to the base metal or to a previous pass.
Cracks: any linear discontinuity in the weld metal or heat-affected zone (HAZ).

Visual inspection of the completed fillet weld can detect surface-breaking porosity and obvious profile defects, but it cannot see what is happening 3 mm below the surface. The break test is the only way to confirm internal soundness without destroying the joint in a more complex fashion. See fillet weld PQR macro examination under AWS D1.1 for the companion macro test that provides fusion geometry data.

Setting up the fillet weld test assembly

The test assembly for fillet weld procedure qualification is a T-joint: a web plate fillet welded to a flange plate. AWS D1.1 Section 6 specifies the minimum dimensions for the test assembly; the plates must be thick enough that the test deposits full-size fillet welds representative of production, and long enough to provide the required number of specimens.

Key variables to record before you strike an arc:

Base metal specification, heat number, and P-number (or equivalent base metal group)
Filler metal lot number, AWS classification, and diameter
Pre-qualified minimum preheat temperature (or the test preheat if the procedure is not prequalified)
Actual electrical parameters: amperage, voltage, polarity
Travel speed measured by timing each pass over a marked distance
Interpass temperature (record with a calibrated contact pyrometer, not a crayon)

These are the values that populate the PQR and that the WPS qualified ranges must support. If you forget to record them during the test weld, you cannot reconstruct them later.

Performing the break

After the test assembly is completed and cooled to ambient temperature:

Make a saw cut or notch through the weld at the mid-point of the test weld length, penetrating approximately halfway through the throat. This notch creates a stress concentration so the weld breaks predictably through the throat rather than peeling off at the root.
Apply load to the web plate to force opening through the weld. This is typically done in a mechanical press, with a hydraulic jack, or by striking the web with a hammer after the assembly is supported on both ends of the flange. The method is less important than the result: the weld must fracture through the throat, not through the base metal.
Examine immediately while the fracture surface is clean and undisturbed. Fracture surfaces oxidize quickly, and re-examination after hours or days is unreliable.

Some shops skip the notch, which increases the chance the assembly will fold rather than break cleanly. A clean fracture through the throat is mandatory — if the base metal tears before the weld separates, the specimen is not a valid break specimen and you must repeat the test.

Acceptance criteria

AWS D1.1 Section 6 sets the break test acceptance criteria. The fractured surface must meet all of the following:

No cracks: any linear discontinuity indicates a procedural problem — typically hydrogen-related cracking, hot cracking, or a severe fusion defect.
No incomplete fusion: the weld metal must show complete fusion to both base metal faces.
Porosity limits: individual pore diameter must not exceed 3/32 in. (2.5 mm), and the sum of pore diameters in any linear inch (25 mm) of weld must not exceed 3/8 in. (9.5 mm). Pore clusters have tighter limits.

These limits apply to the full length of the broken surface — a single large pore near the midpoint fails the specimen even if the rest of the surface is clean.

Rule library based on AWS D1.1:2025; verify against your governing edition, as acceptance limits may differ in the 2020 and earlier editions your contract or AHJ specifies.

Macro examination: the companion test

The break test checks internal soundness; the macro examination checks fusion geometry and weld profile. After the break test, cut a cross-section from the fillet weld (typically near each end of the test assembly), polish and etch the cross-section to reveal the fusion line and HAZ, then examine under low magnification.

The macro must show:

Fusion to the root of the joint (no unfused root gap)
No cracks in the weld metal or HAZ
Leg sizes meeting the minimum specified fillet size
Acceptable weld profile (convexity within code limits, no undercut exceeding the maximum permitted depth)

A specimen that passes the break test can still fail the macro if the root was not fully penetrated. Both specimens must pass independently — passing one does not compensate for failing the other. See how to qualify a welding procedure under AWS D1.1 for the full test sequence from assembly to PQR completion.

Common failure root causes

Break test failures and macro failures rarely come as a surprise if you understand the process:

Porosity: Moisture in the flux or electrode coating, contaminated base metal, or insufficient shielding gas coverage (for GMAW/FCAW-G). Verify electrode condition and storage per AWS A5.1 or A5.20 requirements before testing.

Incomplete fusion at the root: The most common macro failure. Usually caused by incorrect electrode angle, excessive travel speed, insufficient heat input, or root gap too tight for the process. FCAW-S procedures are especially susceptible — the slag system can obscure lack of fusion until the macro shows it.

Cracks: In structural carbon steel fillet welds, cracks on a break test almost always indicate hydrogen-assisted cold cracking. Check preheat against the required minimum, verify that low-hydrogen electrodes were properly dried, and review base metal carbon equivalent.

Undercut exceeding limits: Aggressive travel speed or incorrect electrode angle. Undercut at the weld toe creates a stress riser — the macro reveals severity that a surface inspection might miss.

Documenting results on the PQR

The PQR form must record the break test and macro results with enough specificity that a reviewer can confirm acceptance without re-examining the specimens. At minimum, record:

Break test disposition: acceptable or unacceptable
Nature of any discontinuities observed and dimensions (even accepted ones — recording "porosity, 1/16 in. diameter, isolated" is more defensible than "acceptable")
Macro examination results: fusion to root (yes/no), crack-free (yes/no), fillet leg sizes measured from the etched cross-section
Number of specimens tested and number accepted

Attach photographs of the fracture surface and macro specimen to the PQR package. Most third-party auditors and owners require photographic evidence for new procedure qualifications, and shops that skip photos regret it when a reviewer questions a disposition two years later.

A completed PQR supporting a fillet weld WPS, with break test and macro documentation, is the permanent record that the qualified procedure actually works. Keep it for the life of the WPS — and under AWS D1.1 record retention requirements, that generally means as long as the welds it produced remain in service. See WPS and PQR record retention requirements for the retention obligations.

If your shop runs fillet weld procedures across multiple projects and multiple base metals, a software-managed qualification library lets you track which PQRs support which WPSs, flag when a test value is approaching the edge of a qualified range, and surface the documentation package on demand. Visit our pricing page to see how the platform handles fillet weld PQR tracking alongside groove weld and welder performance records.