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 the shapes of the billets used. Seamless steel pipes are divided into two types: hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes due to their different manufacturing processes. They are mainly used for general structures and mechanical structures. Its representative materials (grades): carbon steel 20, 45 steel; alloy steel Q345, 20Cr, 40Cr, 20CrMo, 30-35CrMo, 42CrMo, etc.