I am a pipe welder for a company that manufactures water purification equipment. Most of the piping we do is sch 10 304L and 316L. We use Argon for a backing gas. We have used several different manufactures of butt weld fittings. Recently we received some butt weld stub ends (type A) that seem to be contaminated somehow. They are coming in sandblasted with aluminum oxide according to the mfg. is this a bad thing? the root passes have black slag type spots on both sides and when welding it seems as though there is not a purge when there is. thanks Sean Snow Water and Power Tech.