321 Fittings cover the standard for wrought austenitic stainless steel fittings for pressure piping applications. The material of pipe fittings shall include forgings, bars, plates or seamless or welded pipes. Forging or forming operations shall be performed by hammering, pressing, piercing, extruding, upsetting, rolling, bending, fusion welding, machining, or a combination of two or more of these operations. All accessories should be heat treated.