welding on a keg

I recently came across two kegs at a garage sale one is a 5 gallon keg with a standard commercial D valve. MY friend has a machine shop and offered to cut off the top and turn it into a corny keg for me. I was wondering what kind of welding to do here. I remember reading about certain kinds that are food grade and some are not.

Thanks

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.
Wheelchair Bob