Discontinuity
Lamellar tearing
A step-like separation in the base metal below a weld, where rolled-in inclusion layers pull apart because the joint loads the plate through its thickness rather than along its rolling direction.
What it looks like
- A terraced or staircase crack path running parallel to the plate surface and stepping between layers
- Located in the base metal outside the heat-affected zone rather than in the weld itself
- Typically found at heavily restrained tee and corner joints on thick rolled plate
- Fracture faces are fibrous and woody-looking, following the flattened inclusion stringers
Causes
- Non-metallic inclusions flattened into layers during hot rolling, giving poor through-thickness ductility
- Joint designs that impose weld shrinkage stress in the short transverse direction of the plate
- High restraint from thick members and rigid fit-up, so shrinkage has nowhere to go but into the plate
- Large weld volumes such as heavy full-penetration tee joints depositing a great deal of shrinking metal
- Hydrogen in the weld, which lowers the stress at which the layers separate
Prevention
- Redesign joints so weld shrinkage pulls along the plate rather than through its thickness
- Specify plate with verified through-thickness properties where the design cannot be changed
- Butter the plate face with a lower-strength ductile layer before making the main weld, to cushion the shrinkage
- Reduce restraint and weld volume, and use balanced welding sequences on heavy joints
How it is found
- UT
- The tears lie parallel to the plate surface, so a straight-beam probe from the face reflects strongly off them and gives clear depth information.
- MT
- Only useful where a tear has broken out to an edge or surface, which happens on the plate edge beside a heavily loaded tee joint.
- VT
- Examination of exposed plate edges after welding can catch a tear that has reached the surface, though most stay buried.
How inspectors think about it
- This is a base metal failure rather than a welding defect, so an inspector's reasoning shifts from weld quality to joint design and material selection.
- The stepped geometry means the flaw can be extensive while showing very little at the surface, so through-thickness examination matters more than surface methods.
- Because repair means excavating into the parent plate, the practical response is often redesign of the connection rather than repeated weld repair.
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
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.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.Slag inclusionNon-metallic slag trapped inside the weld instead of floating to the surface, most often left in a corner or undercut of a previous pass and then buried by the next one.Root crackA crack in or immediately beside the root pass, the thinnest and most highly restrained part of a groove weld, where shrinkage stress from every later pass concentrates on the least metal.
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.