7.2 Guided Bend, Nick Break, and Fillet Weld Break Tests
Key Takeaways
- Guided bend test evaluates weld soundness — specimens are bent 180° around a mandrel
- Three bend types: face (weld face in tension), root (root in tension), side (cross-section, for T > 3/8")
- Bend test acceptance: no open discontinuity exceeding 1/8" (3 mm) in any dimension
- Nick break test breaks specimen open to visually examine internal discontinuities
- Fillet weld break test verifies fusion to the root and internal soundness of fillet welds
- Standard mandrel diameter is 4T (four times specimen thickness)
7.2 Guided Bend, Nick Break, and Fillet Weld Break Tests
Guided Bend Test
The guided bend test is the primary test for evaluating the soundness (freedom from defects) of a welded joint. A rectangular specimen is bent around a mandrel through a specified angle (typically 180°) in a guided bend fixture (jig).
Specimen Types:
| Type | Surface in Tension | Use |
|---|---|---|
| Face bend | Weld face (top surface) | Material ≤ 3/8" thick — tests face soundness |
| Root bend | Weld root (bottom surface) | Material ≤ 3/8" thick — tests root soundness |
| Side bend | Cross-section (side of weld) | Material > 3/8" thick — tests full cross-section |
Acceptance Criteria (AWS D1.1):
- No open discontinuity exceeding 1/8" (3 mm) in any dimension on the convex surface
- Cracks occurring at corners during bending are excluded from consideration (unless they clearly originate from a weld discontinuity)
Mandrel Diameter:
- Typically 4T (four times the specimen thickness) for standard materials
- Wider mandrels (6T or 8T) may be used for materials with lower ductility
Nick Break Test
The nick break test is a simple, practical test designed to reveal internal discontinuities in groove welds:
- Saw cuts (notches) are made on both sides of the weld face and root
- The specimen is broken open through the weld cross-section by bending or impact
- The fractured surface is examined for slag inclusions, porosity, lack of fusion, and other internal discontinuities
Application: Nick break is most commonly used for:
- Pipeline welding (API 1104)
- Quick verification of weld soundness
- Field qualification testing
Acceptance: The fractured surface must show:
- Complete fusion
- No slag inclusions greater than a specified size
- No porosity greater than a specified size
- No lack of fusion visible on the fractured surface
Fillet Weld Break Test
The fillet weld break test examines the soundness of fillet welds:
- A T-joint fillet weld specimen is prepared (one-sided fillet)
- Force is applied to break the fillet weld open from the root
- The broken surface is examined for completeness of fusion, internal porosity, and slag inclusions
Application:
- Welder qualification for fillet welds
- Production quality verification
- Quick soundness check
Acceptance (AWS D1.1):
- The fractured surface must show complete fusion to the root with no inclusions or porosity exceeding a specified size
- The fillet weld convexity must not exceed specified limits
For the Exam: Know the three bend test specimen types (face, root, side) and when each is used. The 1/8" acceptance criteria for bend tests and the nick break test's purpose of revealing internal discontinuities are frequently tested.
When is a side bend test used instead of face and root bend tests?
What is the purpose of the nick break test?