Rectangular pipe is a kind of hollow square section light thin-walled steel pipe, also known as steel refrigerated bending section. It is a section steel with square cross-section shape and size made of Q235 hot-rolled or cold-rolled strip or coil as the base material, which is formed by cold bending and then high-frequency welding. Except for the increased wall thickness, the corner size and edge flatness of the hot-rolled extra-thick-walled square tube reach or exceed the level of the resistance welded cold-formed square tube. Classification of rectangular pipes: steel pipes are divided into seamless steel pipes and welded steel pipes (seamed pipes) hot-rolled seamless square pipes, cold drawn seamless square pipes, extruded seamless square pipes, and welded square pipes.