Beer Forum

I am in the process of designing my new fermenters. I am going to modify (2) half barrels. One being the primary and the other being my secondary. The secondary will be air tight and have a controllable pressure relief valve, so that the beer will be naturally carbonated and mostly sediment free going into the serving kegs. I will need to cut off the half barrel and weld on a new top from a corny keg or possibly a stainless flange. I have a friend that is an exceptional tig welder, but has never had to make food grade sanitary welds. Does anyone know what makes a sanitary weld or most importantly how to make one? I have read that flushing the back side of the weld with gas is how you do it, but there must be more to it than that. I'd really love to hear from someone in the know.