Classification of national standard seamless steel pipes: seamless steel pipes are divided into two categories: hot-rolled and cold-rolled (dial) seamless steel pipes. Hot-rolled seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.
Cold-rolled (drawn) seamless steel pipes include carbon thin-walled steel pipes, alloy thin-walled steel pipes, non-metallic thin-walled Rust thin-walled steel pipe, special-shaped steel pipe.
The outer diameter of hot-rolled seamless pipes is generally greater than 32mm, and the wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless pipes can reach 6mm and the wall thickness can reach 0.25mm. The outer diameter of thin-walled pipes can reach 5mm and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling. Hot-rolled seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.
Generally used seamless steel pipe: it is made of 10, 20, 30, 35, 45 and other high-quality carbon steel 16Mn, 5MnV and other low-alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other alloy steel hot-rolled or cold-rolled. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid transportation pipelines.
6Mn is a kind of material in seamless steel pipes, and it is divided into 4 grades according to the strength: 300, 350, 400 and 450MPa. There are mainly Q295, Q345, Q390, Q420, Q460. ABCD means quality grade Q235 quality grade is divided into A, B, C, D four grades, from A to D means the quality from low to high.
The requirements for different quality levels are as follows:
A—— provide S, P, C, Mn, Si chemical composition and fu, fy, δ5 (δ10), according to the buyer’s needs can provide 1800 cold bending test, but no impact energy requirements, carbon content and Manganese content is not a condition of delivery.
B——provides S, P, C, Mn, Si chemical composition and fu, fy, δ5 (δ10), cold-formed 180‘ test. The shock power Ak≥ 27J C—— at +200C is also provided; in addition to the same requirements as the B class, the shock power Ak≥27J at 00C is also provided.
D—-In addition to the same requirements as the B class, it also provides the impact energy Ak≥27J at -200C E——In addition to the same as the B class requirements, it also provides the impact energy Ak≥27J at -400C.