Pipe fitting is a collective name for the parts in the pipeline system that play a role of connection, control, direction change, shunt, seal, support and so on. Steel pipe fittings are pressure-containing pipe fittings. According to different processing technologies, it is divided into 4 categories, namely butt weldings pipe fittings (with two types: seam pipes and seamless pipes), socket welding and threaded pipe fittings, and flange pipe fittings.