Square and rectangular cold-formed hollow steel, also known as square and rectangular cold-formed hollow steel, referred to as square tube and rectangular tube, code F and J respectively.
Rectangular pipes are classified according to the production process: hot-rolled seamless square pipes, cold-drawn seamless square pipes, extruded seamless square pipes, and welded square pipes.
Among them, the welded square tube is divided into:
1. According to the process-arc welding square tube, resistance welding square tube (high frequency, low frequency), gas welding square tube, furnace welding square tube
2. According to welding seam-straight seam welded square pipe, spiral welded square pipe.