Steel tubes are divided into seamless and welded steel tubes. The seamless steel pipe production process involves piercing a solid billet or ingot into a hollow burr pipe, which is then rolled into a steel pipe of the required size. The different methods of piercing and rolling used constitute different methods of producing seamless steel pipes.
Welded steel pipe production process is the billet (steel plate or strip) bent into a tube, and then welded up the seam into a steel pipe. Because of the different molding and welding methods used, it constitutes a different method of producing welded steel pipe.