Hi all,

I am looking for help regarding the welding of seams of generator housings that we produce.

Short question -

How can porosity occuring in a mild steel welded joint be avoided when plasma arc welding (argon, hydrogen/argon)

Long question -

The raw material is rolled into a cylinder, welded along the seam, then the resulting shell is expanded by ~2%. This expanded shell is then swaged at both ends with the diameter at these regions being increased by a further ~12%.

When the production line was installed initially, and our batch of steel was at a tightly controlled 185MPa yield, the parts went through this process with no problems at all.

Maybe 6 months down the line, we moved onto a new style of steel which was pickled and oiled as opposed to scaled. The yield point of this steel was then found to be substantially higher (~215-225MPa). The carbon content as a result was potentially higher. And to top it all off, the standard of maintenance on the tungsten electrode in the welding torch went downhill.

The parts made around this time, and intermittently ever since have cracked at the swaging process and occasionally even when the parts are expanded.

The welds sometimes appear visibly weak (keyholes in the seam), but at the very least feel brittle when the weld joint is broken between two parts, and the ends of the welds appear porous.

I am aware of the problems associated in terms of hydrogen embrittlement etc, and the quality of the tungsten electrode, but I am quite naive in terms of the whole process in general.

Any help with reducing this porosity problem and the associated weakness would be appreciated!

Thanks