Gebnerally all commercial kegs are stainless and should be TIG welded with Argon on both sides of the weld. The argon provides a blanket that prevents the formation of certain metal byproducts and helps create a homogenous and air tight weld. If your freind has a machine shop, he probably has a tig welder and knows the proper procedure for stainless. If he is even the least bit flaky on answering your weld process querry, you should ask another welder to do the job and keep a freind. Messing up a couple of kegs is NOT the way to cement a long lasting freindship. Stainless requires a specific procedure to do properly and it generally is not cheap because TIG welders that can do it are in high demand for their skill. Joe down at the weldin and truck shop likely isn't the welder you are looking for in this instance.
What do you mean "no Kidneys"???, WTF now I gotta drink less beer...
Join the Automation sub forum in Electric brewing for a discussion of components and control systems. I did!!!!