Steel pipe is a hollow long steel, a large number of pipes used to transport fluids, such as oil, natural gas, water, gas, steam, etc. In addition, in the same bending, torsional strength, lighter weight, so it is also widely used in the manufacture of mechanical parts and engineering structures, but also commonly used for the production of a variety of conventional weapons, gun barrels, shells, etc..

　　Classification of steel pipes: steel pipes are divided into two categories: seamless steel pipes and welded steel pipes (seamed pipes). According to the shape of the section can be divided into round and shaped tube, widely used is round steel pipe, but there are some square, rectangular, semi-circular, hexagonal, equilateral triangle, octagonal and other shaped steel pipe.

　　For steel pipes subjected to fluid pressure are subjected to hydraulic pressure test to test its pressure resistance and quality, under the specified pressure does not occur leakage, wetting or swelling for qualified, some steel pipes also according to the standard or demand side requirements for rolled edge test, flaring test, flattening test, etc..

　　Seamless steel pipe: Seamless steel pipe is made from ingots or solid billets that are perforated into a burr tube and then hot rolled, cold rolled or cold dialed. The specifications of seamless steel pipe are expressed in millimeters of outside diameter * wall thickness. Seamless steel pipe is divided into two categories: hot-rolled and cold-rolled (dialed) seamless steel pipe.

　　Hot-rolled seamless steel pipe is divided into general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, geological steel pipe and other steel pipes, etc.

　　Cold rolled (dial) seamless steel pipe is divided into general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking steel pipe, other steel pipe, including carbon thin-walled steel pipe, alloy thin-walled steel pipe, stainless thin-walled steel pipe, shaped steel pipe.

　　Hot-rolled seamless pipe outer diameter is generally greater than 32mm, wall thickness 2.5-75mm; cold-rolled seamless steel pipe outer diameter can be up to 6mm, wall thickness can be up to 0.25mm, thin-walled tube outer diameter can be up to 5mm wall thickness less than 0.25mm, cold-rolled than hot-rolled high dimensional accuracy.

　　Seamless steel pipe for general use is made of (10, 20, 35, 45) and other good carbon knotted steel 16Mn, 5MnV and other low-alloy structural steel or (40Cr, 30CrMnSi, 45Mn2, 40MnB) and other sintered steel hot-rolled or cold-rolled. Seamless pipes made of low carbon steel such as (10, 20) are mainly used for fluid transportation pipelines. (45, 40Cr) and other medium carbon steel made of seamless tubes are used to manufacture mechanical parts, such as the stressed parts of automobiles and tractors.

　　Seamless steel tubes are generally used to ensure strength and crush test. Hot-rolled steel pipe is delivered in hot-rolled condition or heat-treated condition; cold-rolled is delivered in heat-treated condition.

　　Seamless steel tubes for low and medium pressure boilers: used for manufacturing various low and medium pressure boilers, superheated steam tubes, boiling water tubes, water-cooled wall tubes and superheated steam tubes for locomotive boilers, large smoke tubes, small smoke tubes and arch brick tubes, etc.　Low and medium pressure boilers with good carbon structural steel hot-rolled or cold-rolled (dial) seamless steel tubes, mainly made of (10, 20) steel, in addition to ensuring the chemical composition and mechanical properties to do the hydraulic test, rolled edge, flare, flattening and other tests. Hot-rolled to hot-rolled state delivery, cold-rolled (dial) to heat treatment state delivery.

　　High-pressure boiler steel pipe: mainly used to manufacture high-pressure and above-pressure steam boiler pipes with good carbon structural steel, alloy structural steel and stainless heat-resistant steel seamless steel pipe, these boiler tubes are often in high temperature and high pressure work, the tube in the role of high-temperature flue gas and water vapor will also be oxidation and corrosion, so the steel pipe is required to have a high lasting strength, high oxidation resistance, and has good organizational Stability, the use of steel: excellent carbon structural steel steel (20G, 20MnG, 25MnG); alloy structural steel (15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB); rust heat-resistant steel commonly used (1Cr18Ni9, 1 Cr18Ni11Nb). High pressure boiler tube in addition to ensure the chemical composition and mechanical properties, to do the hydraulic test one by one, to be flaring, flattening test. Steel tube to heat treatment state delivery. In addition, the finished steel pipe microstructure, grain size, decarburization layer also have certain requirements.

　　Seamless steel pipe for geological drilling and petroleum drilling: To find out the underground rock structure, groundwater, oil, natural gas and mineral resources, drilling rigs are used to drill wells. Oil and natural gas extraction is even more inseparable from drilling, and seamless steel pipe for geological drilling and oil drilling is the main equipment for drilling, mainly including core outer pipe, core inner pipe, casing, drill pipe, etc. As the pipe for drilling has to work deep into the stratigraphic depth of several thousand meters, the working conditions are extremely complicated, and the drill pipe is subjected to stresses such as tension, pressure, bending, torsion and unbalanced impact load, and also mud and rock abrasion, therefore, the pipe is required to have sufficient strength, hardness, wear resistance and impact toughness. geological Hanyu Pinyin prefix) plus the number one on behalf of steel yield point, commonly used steel number DZ45 (45MnB, 50Mn); DZ50 (40Mn2, 40Mn2Si); DZ55 (40Mn2Mo, 40MnVB); DZ60 (40MnMoB); DZ65 (27MnMoVB). Steel pipes are delivered in heat-treated condition.

　　Petroleum cracking tubes: Seamless tubes for furnace tubes, heat exchanger tubes and pipelines used in petroleum refineries. Commonly used good carbon steel (10, 20), alloy steel (12CrMo, 15CrMo), heat-resistant steel (12Cr2Mo, 15Cr5Mo), stainless steel (1Cr18Ni9, 1Cr18Ni9Ti) manufacturing. In addition to the chemical composition and various mechanical properties of the steel pipe, but also to ensure the hydraulic pressure, flattening, flaring and other tests, and surface quality and non-destructive testing. Steel tubes are delivered in heat-treated condition.

　　Stainless steel pipe: with a variety of stainless steel hot-rolled, cold-rolled stainless steel pipe, widely used in petroleum, chemical equipment pipelines and various uses of stainless steel structural parts, in addition to the chemical composition and mechanical properties should be guaranteed, where used to withstand fluid pressure of the steel pipe to ensure that the hydraulic test qualified. A variety of special steel pipe to ensure the conditions as specified.