Weld metal that flowed onto a cold surface and froze without melting into it, the shop name for overlap and surface lack of fusion. It often looks fine at a glance, a smooth bead edge with a faint line at the toe, but with no fusion behind that edge it fails bend tests and fatigue loading. It comes from low heat, too much wire, slow travel with the puddle running ahead, and short-circuit MIG on thick plate.
That MIG bead is all cold lap, you can pick at the toe with a fingernail, grind it off and run it hotter.
If a fingernail catches under the edge of a bead, you are looking at cold lap, not a nice toe.
Also heard as
- cold lapping
- overlap
- rollover
- cold roll
Related terms
Lack of fusion
Weld metal that failed to fuse with the base metal or a previous pass at some boundary.
Toe
The edge of a weld bead, where weld metal blends into the surface of the base metal.
Short-circuit transfer
GMAW mode in which the wire touches the pool and shorts many times a second, giving a cool, controllable arc.
Burn-in
Shop word for how deeply a bead melts into the base metal or sidewalls, especially at the root and toes.
Downhill
Welding vertically from the top down, fast and with less heat, as done on cross-country pipelines.