Farm and Workshop Welding. Andrew Pearce

Aligning the edges so there’s no overlap and maybe leaving a small penetration gap is the answer.

       F. Another outside corner, only this time with too much penetration. Weld metal from the first of two runs has oozed right through the joint, either because the gap was too big, the current too high or travel too slow. The sudden change of section at the inner corners will concentrate stress, giving a site for breakage.

       G. That’s better. This T-fillet’s two runs penetrate, fuse to full depth and preserve the parent plate’s section.

       H. Nothing much wrong with this lap joint. But if it’s loaded heavily, failure is likely in the narrow heat-affected zone where grains are coarse and relatively weak (arrow). The torn surface would show a characteristic crystalline structure. There’s not much that can be done, short of post-welding heat treatment to relieve stress and normalize the grain. It’s a common cause of unexpected breakage in welds that otherwise look good.