I am involved in sanitary welding in the maintenance dept of a dairy. Procedures are fairly straight forward and common sense. When welding pipes and fittings, which will be stainless, purging the interior with argon is essential to ensure a decent surface on the inside of the join. Also the fit of the joint to be welded has to be good before you start to ensure that after welding there or no little crevices where bugs can hide and avoid the cleaning fluid, usually a caustic mix. After welding, the weld and surrounding area has to be cleaned using pickling jelly or paste which is applied to the surface and left for ten minutes or so and then washed off. I should add that a TIG welder is the best tool, though I have seen it done with a MIG.
I recently made a tool for semi-automatically welding pipe fitting to valve bodies, as we had over 100 to do. I got a little cheap rotary table, and fixed a three jaw chuck to it. A brass fitting was made to it inside the job with a drilling and a groove to carry the purging argon at the point of weld. The whole assembly was mounted on a plate together with an old indicator stand. The stand was adapted to hold the TIG torch at the correct position. The handle for rotating the table was removed and we now drive the fixture with a cordless drill at low speed. Switch on the purge gas, start the drill, and start the TIG. Result. A perfect weld every time.
