As an important part of steel products, steel pipes are divided into two categories: seamless steel pipes (round billets) and welded steel pipes (plates, strip billets) due to their different manufacturing processes and shapes of the pipe blanks used.
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.
