A crater pipe forms during the final solidified weld pool and is often associated with some gas porosity.
This imperfection results from shrinkage on weld pool solidification. Consequently, conditions which exaggerate the liquid to solid volume change will promote its formation. Switching off the welding current will result in the rapid solidification of a large weld pool.
In TIG (GTAW) welding, autogenous techniques or stopping the wire feed before switching off the welding current, will cause crater formation and the pipe imperfection.
Crater pipe imperfection can be prevented by removing the stop or by welding technique.
|Removal of stop
||- Use a run-off tag in butt joints
|- Grind out the stop before continuing with the next electrode or depositing the subsequent weld run
||- Progressively reduce the welding current to reduce the weld pool size.
- Suitable 'crater filler' devices are available.
- Add filler to compensate for the weld pool shrinkage.
- Welders should receive adequate training.