Crater pipe
A shrinkage cavity left in the crater at the end of a weld bead due to rapid cooling without sufficient filler feed. It acts as a severe notch where fatigue cracks can easily initiate.
The end crater pipe forms at the end of the weld when you break the arc too quickly and the weld pool solidifies without filler material. The metal contracts and forms a funnel-shaped depression, often crossed by fine cracks. The problem is that this area then has a weak, crack-prone structure and can fail quickly under load. To avoid this, you must not end the weld abruptly, but slowly reduce the welding current or briefly dwell on the weld pool until it is completely filled. Alternatively, you can grind the crater area after welding and, if necessary, weld it again. It is important that you fill the end cleanly so that no notch remains.