Mechanical & Weld Laboratory Testing · MECH
Weld Mechanical Testing
Break the coupon so the structure never breaks.
Weld mechanical testing is the destructive examination of welded test coupons — pulling, bending, sectioning and striking machined specimens to prove that a welding procedure or welder produces joints with the required strength, ductility, soundness and toughness. It is the laboratory evidence behind every WPQR and welder qualification certificate.
The explainer
Watch how it works.
Schematic · loops automatically
1Section the coupon
The welded test piece is cut into a specimen set — tensile bars, bend bars, macro slice, impact specimens — to the standard’s map.
2Pull to destruction
The transverse tensile specimen stretches under rising load until fracture: strength recorded, fracture location noted.
3Bend around the former
Root and face bends fold the joint in tension; sound fusion stretches — defects open and fail the test.
4Section, etch, examine
The macro slice is polished and etched: penetration, fusion and imperfections visible; hardness traversed across weld and HAZ.
5Strike for toughness
Where specified, Charpy specimens are broken at temperature — absorbed energy proves resistance to brittle fracture.
The physics
A weld must not be the weak link, and mechanical testing asks that directly. The transverse tensile test (ISO 4136 for welds; parent metal to ISO 6892-1) machines a specimen across the joint and pulls it to destruction: the joint must meet the parent material’s specified tensile strength, and where it breaks is recorded as carefully as the number — a fracture in parent metal is the quiet pass every procedure wants.
Bend tests (ISO 5173) interrogate ductility and fusion: specimens are folded over a former to a specified angle with the weld root or face in tension. Sound, fused metal stretches; lack of fusion, root defects and brittle zones open into visible fissures. The macro-examination (ISO 17639) completes the picture — a polished, etched cross-section that shows penetration, fusion profile and imperfections, with a hardness traverse (ISO 9015-1) mapping HAZ hardening against procedure limits.
Where service is cold or the code demands toughness, Charpy V-notch impact tests (ISO 148-1) strike notched specimens at temperature and measure absorbed energy — the resistance to brittle fracture that tensile numbers cannot reveal. Together the suite converts “the welder says it’s fine” into accredited laboratory evidence, which is exactly what a WPQR is.
Where it earns its keep
Typical applications
- Welding procedure qualification (ISO 15614-1 / ASME IX) test programmes
- Welder qualification coupon testing (EN ISO 9606-1)
- Production weld test plates on critical contracts
- Failure investigation comparison testing
Standards & schemes
| Designation | Covers |
|---|---|
| ISO 4136 / ISO 6892-1 | Transverse tensile testing of welds / tensile testing of metallic materials |
| ISO 5173 | Bend testing of welds |
| ISO 17639 / ISO 9015-1 | Macroscopic examination and hardness testing of welded joints |
| ISO 148-1 | Charpy V-notch impact testing |
Specimens are machined and tested in the laboratory with calibrated machines under Metlab’s quality system, reported as the evidence pack behind WPQRs and welder certificates.
Why does the fracture location in a tensile test matter?
A specimen that breaks in the parent metal proves the weld is at least as strong as the material it joins — the design assumption. A weld-metal fracture can still pass on numbers, but it prompts a harder look at procedure and consumables. The location is metallurgy speaking.
What does a failed bend test actually mean?
Bends are merciless with fusion defects: a root bend that opens a fissure is usually revealing lack of root fusion or penetration that radiography might have shown and tensile testing might have missed. It fails the qualification — and it is exactly the defect you want discovered on a coupon, not a pipeline.
When are Charpy impact tests required?
Whenever the application faces low temperatures or the code demands proven toughness — pressure equipment categories, offshore and structural specifications with minimum design temperatures. Requirements are code-specific: we build the specimen and temperature matrix from the governing specification.
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