D1.1 Fillet Weld Break Test — §6.23.4 Procedure, Figure 6.23 Specimen, and §6.23.4.1 Acceptance
The AWS D1.1:2025 fillet weld break test bends a 6-inch [150 mm] welder qualification specimen until it fractures or folds flat. Per §6.23.4.1, the broken fracture surface must show complete fusion to the root with no inclusions or porosity larger than 3/32 in [2.5 mm].
Almost every welder qualification disagreement on the shop floor comes down to one bend test. A weld that looks symmetric, has no surface porosity, and passes visual inspection can still hide cold lap at the root corner — and the §6.23.4 break test is what surfaces that defect when a destructive macroetch is not run.
What the Fillet Weld Break Test Proves
The AWS D1.1:2025 fillet weld break test is one of the four destructive tests available for welder, welding operator, and tack welder performance qualification under Clause 6 Part C. The other three are face bend, root bend, and side bend per §6.10.3, and the all-weld-metal tension test per §6.10.3.6. The break test is unique because it targets the root fusion zone — the most common failure plane on a fillet weld — rather than the gross strength of the deposit.
Lack of fusion at the root corner is the failure mode the test is designed to catch. A fillet weld that visually appears symmetric, has acceptable bead profile, and shows no surface porosity can still contain a cold lap at the root because the puddle never wetted into the root corner during welding. Visual inspection per §8.9 cannot see this defect: the root is buried inside the joint geometry. The break test loads the specimen so the root is in tension, opening the weld along its weakest plane. The fillet-weld-strength assumptions on the fillet weld size calculator — effective throat times allowable shear — only apply when the root fusion the break test verifies is actually present.
The §6.23.4 Procedure Step by Step
The entire lengths of the fillet weld shall be examined visually, and then a 6 in [150 mm] long specimen (see
AWS D1.1:2025 §6.23.4Figure 6.23) or a quarter-section of the pipe fillet weld assembly shall be loaded in such a way that the root of the weld is in tension. At least one welding start and stop shall be located within the test specimen. The load shall be increased or repeated until the specimen fractures or bends flat upon itself.
The procedure has four operational steps. (1) Visual inspection of the entire weld length on the as-welded test plate before any cutting. (2) Specimen extraction — cut a 6 in [150 mm] long section from the plate, or use a quarter-section if the test was on pipe. (3) Load orientation — clamp or position the specimen so the root of the fillet weld is on the tension side when load is applied. The mechanism may be a press, a hydraulic ram, or a manually-driven force fixture; the code does not prescribe the apparatus. (4) Apply load until the specimen either fractures or bends flat upon itself. The load may be a single increasing force or repeated cycles.
The at least one start-stop requirement is intentional: weld start-stops are statistically the highest-risk locations for tie-in defects, so the specimen must contain at least one to test the welder ability to manage start-stop fusion, not just steady-state bead deposition.
Specimen Geometry — Figure 6.23
Figure 6.23 specifies the welder and welding operator fillet weld break and macroetch test plate. The geometry is a T-joint: a vertical plate welded to a horizontal base plate with the production fillet weld on one side. The minimum dimensions are:
- Vertical plate height: 6 in [150 mm] minimum
- Base plate width: 4 in [100 mm] minimum
- Fillet weld size: 1/2 in [12 mm] minimum
- Single-pass weld minimum: 1/4 in [6 mm]
- Total weldment length L: 8 in [200 mm] minimum for welders, 15 in [380 mm] minimum for welding operators
- Start-stop location: stop and restart welding near the center of the weldment
After welding, the assembly is sectioned at the cut lines indicated in the figure. Either end of the weldment may be used for the break specimen, and the other end may be used for the required macroetch specimen. The unused portion is discarded. This dual-use design lets one welder qualification test plate produce both the fillet weld break specimen for §6.23.4 and the macroetch specimen for §6.23.2 without welding two separate plates.
§6.23.4.1 Acceptance Criteria
The acceptance test has two stages: visual exam before the break, and inspection of the broken specimen after the break.
Visual examination prior to the break test. Per §6.23.4.1, the weld shall present a reasonably uniform appearance and shall be free of overlap, cracks, and undercut in excess of the requirements of §8.9. There shall be no porosity visible on the weld surface. A specimen that fails this visual gate is not eligible to proceed to the destructive break.
The broken specimen shall pass if either of two conditions is met:
- The specimen bends flat upon itself, or
- The fillet weld, if fractured, has a fracture surface showing complete fusion to the root of the joint with no inclusion or porosity larger than 3/32 in [2.5 mm] in greatest dimension.
Either path is sufficient. A bent-flat specimen demonstrates ductility and adequate fusion without revealing the fracture surface; a fractured specimen requires fracture-surface examination for the two named defects. The 3/32 in [2.5 mm] dimensional limit applies to the greatest dimension of any individual inclusion or porosity, not the cumulative count.
Visual Acceptance — §8.9 and Table 8.1
The visual gate before the break test references §8.9, which is the production weld visual inspection clause. Per §8.9, all welds shall be visually inspected and shall be acceptable if the criteria of Table 8.1, or Table 10.14 if tubular, are satisfied. Table 8.1 sets the quantitative limits on the four named visual defects: undercut, profile, fusion, and crater fill. The fillet weld break test specimen must clear Table 8.1 limits before the destructive load is applied.
The undercut tolerance is the most-cited example: Table 8.1 permits undercut up to 1/32 in [1 mm] depth on a statically-loaded fillet weld with thickness less than 1 in [25 mm]. Undercut deeper than 1/32 in [1 mm] disqualifies the specimen at visual inspection — the welder cannot proceed to the break test until the visual fail is addressed by either grinding-and-revisual or rewelding.
Tack Welder Variant — §6.24 and Figure 6.27
Tack welder qualification uses a parallel but distinct fillet weld break test. The differences are in specimen geometry, weld size, and acceptance language.
Per §6.18.2, the tack welder makes a 1/4 in [6 mm] maximum size tack weld approximately 2 in [50 mm] long on the fillet-weld-break specimen shown in Figure 6.27. Figure 6.27 is smaller than Figure 6.23: a 4 in [100 mm] by 4 in [100 mm] square plate with a 1/2 in [12 mm] thick top section and a 2 in [50 mm] wide tack weld area.
Per §6.24, a force is applied to the specimen as shown in Figure 6.20 until rupture occurs. The force may be applied by any convenient means. The acceptance criterion in §6.24.2 reads: the fractured surface of the tack weld shall show fusion to the root, but not necessarily beyond, and shall exhibit no incomplete fusion to the base metals or any inclusion or porosity larger than 3/32 in [2.5 mm] in greatest dimension.
The key linguistic difference from §6.23.4.1 is fusion to the root, but not necessarily beyond versus complete fusion to the root. A tack weld is a temporary fixturing weld and is not expected to develop the deposit profile of a production fillet, so the code permits less depth past the root corner. The 3/32 in [2.5 mm] porosity limit is identical to the welder-qualification rule.
Related Standards Guides
Frequently Asked Questions
What is the AWS D1.1 fillet weld break test?
The AWS D1.1:2025 fillet weld break test is a destructive performance qualification test used to qualify welders, welding operators, and tack welders. Per §6.23.4, a 6 inch [150 mm] long specimen of completed fillet weld is loaded so that the root of the weld is in tension, and the load is increased or repeated until the specimen either fractures or bends flat upon itself. The test exposes the root fusion zone — the most likely site of cold lap or lack of fusion — by physically opening the weld at its weakest plane. Visual inspection alone cannot confirm root fusion on a fillet weld because the root is buried inside the joint geometry. The break test is paired with a macroetch test on the other end of the same specimen plate per Figure 6.23 to give a destructive look at internal soundness.
How is the fillet weld break test specimen prepared per Figure 6.23?
Figure 6.23 specifies a T-joint test plate where a vertical plate is welded to a horizontal base plate with the production fillet weld. Minimum dimensions are 6 inches [150 mm] vertical plate height, 4 inches [100 mm] base plate width, 1/2 inch [12 mm] fillet weld size, and 1/4 inch [6 mm] single-pass weld. Total weldment length L is 8 inches [200 mm] minimum for welders and 15 inches [380 mm] minimum for welding operators. The welder must stop and restart welding at least once near the center of the weldment so that a start-stop is captured inside the test specimen. After welding, the assembly is sectioned: one end yields the 6 inch break specimen, and the other end yields the macroetch specimen. Either end may serve either role, and the unused end is discarded.
What is the §6.23.4.1 acceptance criterion for a passed break test?
Per AWS D1.1:2025 §6.23.4.1, a fillet weld break test passes if the broken specimen meets either of two outcomes. The first acceptance path is that the specimen bends flat upon itself without fracturing — this demonstrates ductility and adequate fusion. The second path is that if the specimen does fracture, the fracture surface must show complete fusion to the root of the joint and contain no inclusion or porosity larger than 3/32 inch [2.5 mm] in greatest dimension. Either condition is sufficient. Visual inspection prior to the break is also a precondition: per §6.23.4.1, the weld shall present a reasonably uniform appearance and shall be free of overlap, cracks, and undercut in excess of §8.9 limits, and there shall be no porosity visible on the weld surface.
Does the weld need to fracture, or can it bend flat?
Either outcome passes per §6.23.4.1. A weld that bends flat upon itself without fracturing is the cleanest pass — the load was applied, the specimen yielded ductility, and no fracture surface needs to be examined. A specimen that does fracture is not automatically a fail; it must be examined for two specific defects on the fracture surface: any incomplete fusion to the root, and any inclusion or porosity larger than 3/32 in [2.5 mm] in greatest dimension. The test is structured this way because both outcomes signal adequate strength. A ductile weld bends; a stronger-than-base-metal weld may fracture in the heat-affected zone or base metal rather than the weld itself, which is also acceptable. The pass criterion focuses on what the fracture surface reveals, not whether fracture occurred.
What is the difference between the welder break test and the tack welder break test?
The welder qualification break test under §6.23.4 uses the Figure 6.23 T-joint test plate and applies the §6.23.4.1 criterion of complete fusion to the root with no porosity larger than 3/32 in [2.5 mm]. The tack welder break test under §6.24 uses Figure 6.27 — a smaller plate where the tack welder makes a 1/4 inch [6 mm] maximum size tack weld approximately 2 inches [50 mm] long per §6.18.2. The tack welder acceptance criterion in §6.24.2 is more lenient: the fracture must show fusion to the root but not necessarily beyond, no incomplete fusion to the base metals, and the same 3/32 inch [2.5 mm] porosity limit. The key difference is the words complete fusion in §6.23.4.1 versus fusion to the root in §6.24.2 — tack welds need only reach the root, not extend through to the back face.
Can a fillet weld pass visual inspection but fail the break test?
Yes — and this is the failure mode the break test is designed to catch. A fillet weld can pass visual inspection per §8.9 and Table 8.1 with a reasonably uniform appearance, no surface porosity, no overlap, no cracks, and acceptable undercut, while still containing a cold lap or lack of fusion at the root corner. The root is buried inside the joint geometry, so visual inspection cannot see it. Common causes are insufficient heat at the start of the weld, fast travel speed that prevents the puddle from wetting into the root corner, or a wire angle that lays bead on top of the joint rather than into it. The break test exposes this defect by loading the root in tension. A pretty weld that fails the break test is the most common qualification failure in shop practice and the reason §6.23.4 exists alongside §8.9 visual inspection.
When can an Inspector require a fillet weld break test under §8.4.2?
AWS D1.1:2025 §8.4.2 gives the Inspector explicit authority to require additional qualification testing when production weld quality appears below code requirements. The clause states that when the quality of a qualified welder, welding operator, or tack welder work appears to be below the requirements of this code, the Inspector may require the welder to demonstrate ability to produce sound welds by means of a simple test, such as the fillet weld break test, or by requiring complete requalification in conformance with Clause 6 or Clause 10 for tubulars. The fillet weld break test is named in the code as the simple test option because it is fast, requires no NDE equipment, and gives an unambiguous accept-or-reject result. This authority does not require a contract amendment; it is built into the inspector role per §8.1.2 and §8.4.2.
CWI Exam Tip: Part B and Part C frequently ask for the §6.23.4.1 dual-acceptance rule (bends flat OR fracture surface shows complete root fusion plus no porosity larger than 3/32 in [2.5 mm]). A common distractor is the tack welder §6.24.2 criterion (fusion to the root, but not necessarily beyond) — if the question stem says welder, complete fusion is required; if it says tack welder, fusion to the root only.