Old SS welding wire

Yes SS solid wire does oxidize but once it covered with a oxidized layer it won't go much deeper with time. I would look at how dirty it is, oil would be a big concern as well a surface rust if any. Surface rust would come from someone grinding mildsteel in the direction of the wire spool and it's the mild steel thats rusting, depending on the type of SS.

Another concern what type of SS wire is it?, 304 308, 316, or 400 series? 316 don't like to be welded with 304, etc. If it isn't marked it would have to be dirt cheap to mess with it.

I just put on a roll of E70S and a rat had pi$$ed on the roll. I've pulled off probably two pounds and still hit rat pi$$ wire. I'm going to pull off another 2lbs and if that don't help, I'm going to chuck it as it's not worth replacing a new liner.

T_Bone

Yes it should work "ok" although 309 would work best. I would imanage you will see a dark weld bead with alot of carbon on the surface. You didn't say what size pipe?, plate?. That might change things but if not a pressure joint I'm not to concerned.

T_Bone

T_Bone

Yep I do cut mine for Tig sometimes but you did catch a mistake, Thanks. That should read 308. I've got 304 on my mind as I'm building tanks right now.

T_Bone

If you are joining dissimilar grades of austenitic stainless steel the 309 designation is best suited.

Most of what you will run across in agricultural applications is 304 S.S. and generally speaking, in the food industry, you will find 316 or 316L.

Some 400 series will be found in industrial applications involving pump parts, etc. These are all austenitic types.

The rules can change considerably outside the realm of the austenitic grades.
HTH,
Steve