Destructive Testing
Destructive Testing covers the mechanical tests that qualify procedures and verify production welds, plus how specimens are made, tested, and judged. The reference standards are AWS B4.0 for mechanical testing and the qualification clauses of the construction code, typically AWS D1.1 Clause 4.
The tests
- Transverse tension: a coupon cut across the weld and loaded to failure. It reports tensile strength and reveals defects by where it breaks; a break in the weld with a visible defect is a failure even if the strength number is met.
- Guided bend: side bend for thicker plate, face and root bend for thinner. The specimen wraps around a plunger and the outer surface is examined after bending.
- Nick-break: a saw cut along the weld, then fracture; the face exposes slag, porosity, and fusion defects. Common for pipe.
- Fillet weld break: a loaded fillet is broken to expose the root and fusion boundaries.
- Charpy V-notch: toughness at a stated temperature.
- Hardness and macroetch: hard phase and profile checks on low-alloy and high-strength work.
Judging specimens
Visual examination happens before testing. After bending, the convex surface is inspected; D1.1 limits any single indication to about 1/8 in and the sum of smaller indications to about 3/8 in along the specimen, with corner and edge conditions handled separately. Every code states its own limits, so cite the one in force.
Worked example
A 3/8 in plate procedure test produces four side bend specimens. One shows a 3/16 in indication at the fusion line. The indication exceeds the single-indication limit and sits at the fusion boundary, so it points to lack of fusion rather than to a ductility problem. The procedure fails, and the investigation turns to heat input, travel angle, and interpass cleaning rather than to bending technique. Code retest provisions allow a limited retest using new specimens cut from the same coupon.
Traps
Mistaking machining marks for defects; confusing face and root bends; assuming a tension test passes because the number is high when the break location says otherwise.