Seamless steel pipes are divided into two types: hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes due to different manufacturing processes. Cold drawn (rolled) pipes are divided into round pipes and special-shaped pipes. Hot rolling (extruded seamless steel pipe): round tube blank → heating → perforation → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → billet tube → straightening → quality inspection Wall thickness → hydrostatic test (or flaw detection) → marking → storage.
Cold drawn (rolled) seamless steel pipe: round tube blank → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → Quality inspection of wall thickness → hydrostatic test (flaw detection) → marking → storage. GB/T8162-2008 (seamless steel pipe for structural use). Mainly used for general structures and mechanical structures. Its representative materials (grades): carbon steel No. 20, No. 45 steel; alloy steel Q345, 20Cr, 40Cr, 20CrMo, 30-35CrMo, 42CrMo, etc.