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Steel pipe is a kind of hollow long strip steel material, widely used as a pipeline for conveying fluids such as oil, natural gas, water, gas, steam, etc. In addition, under the same bending and torsional strength, it is lighter in weight, so it is also widely used in the manufacture of mechanical parts and engineering structures. It is also commonly used in the production of various conventional weapons, gun barrels, shells, etc.
Steel pipes are divided into two categories: seamless steel pipes and welded steel pipes (seamed pipes). According to the cross-sectional shape, they can be divided into round pipes and special-shaped pipes. The widely used ones are round steel pipes, but there are also some special-shaped steel pipes such as square, rectangular, semi-circular, hexagonal, equilateral triangle, octagonal, etc. For steel pipes that bear fluid pressure, hydraulic tests must be carried out to test their pressure resistance and quality. Under the prescribed pressure, there must be no leakage, wetting, or expansion to be qualified. Some steel pipes must also undergo crimping tests, flaring tests, flattening tests, etc., according to standards or requirements.
Seamless steel pipes: Seamless steel pipes are made from steel ingots or solid tube billets through piercing to make capillary tubes, then through hot rolling, cold rolling, or cold drawing. The specifications of seamless steel pipes are expressed in millimeters by outer diameter * wall thickness. Seamless steel pipes are divided into hot-rolled and cold-rolled (drawn) seamless steel pipes. Hot-rolled seamless steel pipes include 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. In addition to the general steel pipes, low and medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, and petroleum cracking pipes, cold-rolled (drawn) seamless steel pipes also include carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless thin-walled steel pipes, and special-shaped steel pipes. The outer diameter of hot-rolled seamless pipes is generally greater than 32mm, wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless steel pipes can reach 6mm, wall thickness can be 0.25mm. The outer diameter of thin-walled pipes can be 5mm, wall thickness less than 0.25mm. The dimensional accuracy of cold-rolled is higher than that of hot-rolled. General-purpose seamless steel pipes are made from high-quality carbon structural steels such as 10, 20, 30, 35, 45, and low alloy structural steels such as 16Mn, 5MnV, or 40Cr, 30CrMnSi, 45Mn2, 40MnB, etc., through hot or cold rolling. Seamless pipes made of low-carbon steel such as 10, 20 are mainly used for fluid conveying pipelines. Seamless pipes made of medium carbon steel such as 45, 40Cr are used to manufacture mechanical parts, such as stressed parts of automobiles, tractors, etc. General seamless steel pipes must ensure strength and flattening tests. Hot-rolled steel pipes are delivered in hot-rolled or heat-treated state; cold-rolled is delivered in heat-treated state.
Low and medium pressure boiler seamless steel pipes: Used for manufacturing various low and medium pressure boilers, superheated steam pipes, boiling water pipes, water-cooled wall pipes, and superheated steam pipes, large smoke pipes, small smoke pipes, and arch brick pipes for locomotive boilers, etc. Made from high-quality carbon structural steel through hot or cold rolling (drawing) seamless steel pipes. Mainly made from No. 10, 20 steel. In addition to ensuring chemical composition and mechanical properties, hydraulic tests, crimping, flaring, flattening, and other tests must be done. Hot rolling is delivered in hot-rolled state, cold rolling (drawing) is delivered in heat-treated state.
High-pressure boiler steel pipes: Mainly used to manufacture high-pressure and above-pressure steam boiler pipes, etc., made from high-quality carbon structural steel, alloy structural steel, and stainless heat-resistant steel seamless steel pipes. These boiler pipes are often under high temperature and high pressure during work. Under the action of high temperature flue gas and water vapor, the pipes will oxidize and corrode, so the steel pipes are required to have high endurance strength, high anti-oxidation performance, and good organizational stability. The steel grades used are: high-quality carbon structural steel grades 20G, 20MnG, 25MnG;
Alloy structural steel grades: 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB, etc.;
Stainless heat-resistant steel commonly used: 1Cr18Ni9, 1Cr18Ni11Nb. In addition to ensuring chemical composition and mechanical properties, high-pressure boiler pipes must undergo hydraulic tests for each pipe. Flaring and flattening tests must be conducted. Steel pipes are delivered in heat-treated state. In addition, the finished steel pipes' microstructure, grain size, and decarburization layer also have certain requirements. Geological drilling and petroleum drilling seamless steel pipes; To ascertain the underground rock formations, groundwater, oil, natural gas, and mineral resources, drilling rigs are used to drill wells. Oil and natural gas exploitation is also inseparable from drilling wells, geological drilling.
Seamless steel pipes for petroleum drilling are primary tools for drilling wells, mainly including core outer pipes, core inner pipes, casings, and drill pipes. Because drilling pipes need to work at depths of several thousand meters, the working conditions are extremely complex. The drill pipe withstands tensile, compression, bending, torsion, and uneven impact loads, among other stress actions, and it must also resist mud and rock wear. Therefore, the pipe materials must have sufficient strength, hardness, wear resistance, and impact toughness. The steel grades for steel pipes are represented by "DZ" (the Chinese phonetic alphabets for "Geology") plus a number to indicate the steel yield point. Common steel grades are DZ45: 45MnB, 50Mn; DZ50: 40Mn2, 40Mn2Si; DZ55: 40Mn2Mo, 40MnVB; DZ60: 40MnMoB; DZ65: 27MnMoVB. Steel pipes are delivered in heat-treated state.
Petroleum cracking pipes: Used in the furnace pipes, heat exchanger tubes, and seamless pipes for the pipelines in petroleum refineries. Commonly made from high-quality carbon steel (10, 20), alloy steel (12CrMo, 15CrMo), heat-resistant steel (12Cr2Mo, 15Cr5Mo), and stainless steel (1Cr18Ni9, 1Cr18Ni9Ti). In addition to ensuring chemical composition and various mechanical properties, steel pipes must also ensure hydraulic tests, flattening, flaring tests, surface quality, and non-destructive inspection. Steel pipes are delivered in heat-treated state.
