Cluster Porosity

Porosity clusters form when gases like hydrogen or oxygen can't escape the weld pool in time and get trapped as bubbles. Often caused by damp workpieces, dirty filler materials, or a too-cold weld pool. That stuff is tough and makes the weld porous, so it won't hold up under load anymore. To avoid it: clean the material, keep it dry, and put in enough heat so the pool stays fluid enough for gases to rise out. If you see a porosity cluster, grind or mill it out and reweld – bridging over it won't help.