Discontinuity
Transverse crack
A crack running across the weld axis, at right angles to the direction of travel, caused by longitudinal shrinkage stress in a weld that is stronger or harder than the metal around it.
What it looks like
- Short cracks crossing the bead face, sometimes evenly spaced along a length of weld
- May stop at the weld toes or continue into the heat-affected zone and base metal
- Frequently found on high-strength deposits and on hardfacing overlays where they are expected
- Tight, sharp-edged, and often only visible after the bead is wire-brushed or lightly ground
Causes
- Longitudinal contraction of the weld metal restrained by the length of the joint
- Weld metal with higher strength and lower ductility than the base metal, which cannot yield to relieve the stress
- Hydrogen dissolved in the deposit, which lowers the stress needed to initiate a crack after cooling
- Rapid cooling in thick sections producing hard, low-toughness microstructure through the deposit
- Multipass welding without preheat, letting each pass add restraint to an already stressed joint
Prevention
- Match filler metal strength to the base metal rather than reaching for the strongest available
- Preheat and hold interpass temperature so the deposit cools slowly and hydrogen can diffuse out
- Use genuinely low-hydrogen consumables handled and stored to keep them that way
- Apply post-weld heat treatment on heavy restrained sections where residual stress cannot otherwise be relieved
How it is found
- MT
- A field applied along the weld axis leaks strongly at a crack lying across it, giving a crisp particle indication perpendicular to the bead.
- PT
- Effective on austenitic and non-ferrous material where magnetic methods do not work, provided the crack reaches the surface.
- RT
- Detectable when the beam happens to align with the crack plane, but transverse cracks are easily missed on film if the angle is wrong.
- UT
- Angle-beam scanning from both sides and along the weld gives the beam a chance to strike the crack face squarely and return a sharp echo.
How inspectors think about it
- A crack lying across the direction of principal stress sits in the worst possible orientation, because the applied load pulls directly on the crack faces and drives it open.
- Because transverse cracking often signals hydrogen or an over-matched filler metal, inspectors treat it as evidence of a systemic problem rather than an isolated defect.
- Delayed cracking is a real concern with high-strength deposits, so final inspection is often held off for a period after welding rather than done while the joint is still warm.
General reasoning only. The accept/reject limits for your work come from the code or specification governing the job, which this site does not reproduce.
Related discontinuities
Longitudinal crackA crack running parallel to the weld axis, either down the centreline of the bead or along the fusion line, driven by shrinkage stress acting across the joint as the deposit cools and contracts.Cold crack (hydrogen-induced cracking)A crack that appears after the weld has cooled, sometimes many hours later, when dissolved hydrogen collects at defects in a hard microstructure and residual stress finishes the job.Underbead crackA crack lying in the heat-affected zone beneath a sound-looking weld bead, produced by hydrogen trapped in hard martensite that cracks under residual stress after the joint has cooled.Toe crackA crack starting at the junction of the weld face and the base metal, where the abrupt change in section concentrates stress and the heat-affected zone is at its hardest and least forgiving.
Can you name it on sight?
The gauge trainer's identification mode shows you a weld and four names. Reading about porosity and picking it out of a line-up are not the same skill.