Stainless Q&A

Q: Why do root surfaces of stainless steel pipe welds discolor, and is this a problem? I understand purging during welding will reduce this. Are there documents that address purging?

A: Discoloration is caused by different compositions and thicknesses of oxides and hydroxides that form in air and can reduce corrosion resistance. AWS publishes several standards addressing this.

Probably the best document is AWS D10.4, Guide for Welding Austenitic Stainles..