Crater Crack — What It Is and Why It Matters
A crater crack is a crack that forms in the depression (crater) left at the end of a weld bead when the arc is extinguished. As the small remaining pool solidifies, the contraction forces exceed the still-hot metal's strength, causing a star-shaped or linear crack in the crater.
Crater cracks are one of the most common and preventable weld defects. They occur because the welder simply stopped the arc without filling the crater — the abrupt termination creates a concave depression that concentrates shrinkage stress as it cools.
Prevention is straightforward: fill the crater before breaking the arc. In TIG welding, gradually reduce amperage with the foot pedal while adding filler to fill the crater smoothly. In MIG welding, pause briefly at the end to build up the crater, or use the crater-fill function if the machine has one. In stick welding, reverse direction briefly at the bead end to fill the crater, or strike a new arc in the crater to fill it.
Frequently Asked Questions
Why do crater cracks matter?
A crater crack is a real crack — it can propagate under load or thermal cycling, extending into and through the weld bead. In fatigue-loaded or code-governed structures, crater cracks are rejectable defects. Even in non-critical work, they indicate poor termination technique that should be corrected.
Do all welding processes get crater cracks?
Crater cracks can occur with any arc welding process, but they are most common in TIG welding (where the welder controls heat tapering manually) and in any process where the arc is terminated abruptly without crater filling. Modern MIG and TIG machines include crater-fill functions specifically to address this issue.