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)
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?