In appearance, seamless steel pipe and straight seam welded pipe are different in the inner wall of the welded pipe with welding bars, and seamless without. 2. The pressure of the seamless pipe is higher, and the welded pipe is generally about 10 MPa. Now the welded pipe is made seamless. 3. Seamless steel pipe is formed once in rolling. Welded steel pipe needs to be rolled after welding, generally spiral welding and straight welding. Performance seamless pipe better, of course, the price is also higher. Steel pipe is a kind of hollow strip of steel, a large number of used for conveying fluid pipelines, such as oil, gas, water, gas, steam, etc., in addition, bending, torsional strength is the same, light 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 conventional weapons, gun barrels, shells, etc. Classification of steel pipe: steel pipe is divided into seamless steel pipe and welded steel pipe (with seam pipe) two categories. According to the shape of the section can be divided into round pipe and special-shaped pipe, widely used is circular steel pipe, but there are also some square, rectangular, semicircle, hexagonal, equilateral triangle, octagonal special-shaped steel pipe. For the steel pipe under fluid pressure to carry out hydraulic tests to test its pressure resistance and quality, under the specified pressure does not leak, wetting or expansion for qualified, some steel pipe according to the standard or requirements of the demander to roll test, flaring test, flattening test, etc. Seamless steel tube: Seamless steel tube is made of steel ingot or solid tube billet through perforation, and then hot rolled, cold rolled or cold drawn. The specifications of seamless steel tubes are expressed as outer diameter * wall thickness in millimeters. Seamless steel tubes are divided into hot rolled and cold rolled seamless steel tubes. 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 pipe. In addition to the general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, other steel pipes, cold rolled seamless steel pipe also includes carbon thin wall steel pipe, alloy thin wall steel pipe, stainless steel pipe, special-shaped steel pipe. The outer diameter of hot rolled seamless pipe is generally greater than 32mm, the wall thickness is 2.5-75mm, the diameter of cold rolled seamless steel pipe can be 6mm, the wall thickness can be 0.25mm, the outer diameter of thin wall pipe can be 5mm, the wall thickness is less than 0.25mm, the cold rolling is higher than the hot rolling size accuracy. Generally used seamless steel tubes are made of 10, 20, 30, 35, 45 and other high quality carbon bonded steel 16Mn, 5MnV and other low alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other bonded steel hot rolled or cold rolled. 10, 20 and other low carbon steel made of seamless pipe is mainly used for fluid conveying pipeline. 45, 40Cr and other medium carbon steel made of seamless pipe to manufacture machine parts, such as cars, tractors, force parts. Generally use seamless steel pipe to ensure strength and flattening test. Hot rolled steel pipes are delivered in hot rolled or heat treated state; Cold rolling is delivered in hot or heat treated state. Seamless STEEL TUBE FOR low and medium PRESSURE BOILER: USED for manufacturing all kinds of low and medium pressure boiler, superheated steam tube, boiling water tube, water wall tube and superheated steam tube for locomotive boiler, large smoke pipe, small smoke pipe and arch brick pipe, etc. Hot – rolled or cold – rolled seamless steel tubes with high quality carbon structural steel. Mainly made of 10, 20 steel, in addition to ensure chemical composition and mechanical properties to do hydraulic test, rolling, flaring, flattening and other tests. Hot rolling is delivered in hot rolling state, cold rolling (dialing) is delivered in heat treatment state. High pressure boiler steel pipe: Mainly used in the manufacture of high pressure and over pressure steam boiler pipes, etc. With high quality carbon structural steel, alloy steel and stainless heat resistant steel seamless steel tube, the boiler tube by the party under high temperature and high pressure pipe and works in high temperature flue gas and steam will happen under the action of oxidation and corrosion, so the steel pipe with high rupture strength, high oxidation resistance, And has good organizational stability, using steel: high quality carbon structural steel steel has 20G, 20MnG, 25MnG; 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB, etc. There are rust heat resistant steel commonly used 1Cr18Ni9, 1Cr18Ni11Nb high pressure boiler tube in addition to ensure chemical composition and mechanical properties, to do hydraulic test root by root, to do flaring, flattening test. Steel tubes are delivered in a heat treated state. In addition, the microstructure, grain size and decarbonization layer of the finished steel pipe are also required. Seamless steel tubes for geological drilling and petroleum drilling control; Drilling RIGS are used to drill Wells in order to find out the structure of underground strata, groundwater, oil, natural gas and mineral resources. Oil and natural gas exploitation is more inseparable from drilling, geological drilling control oil drilling seamless steel pipe is the main drilling equipment, mainly including core outer pipe, core inner pipe, casing, drill pipe, etc.. Due to the drilling pipe to go deep into thousands of meters of stratum depth work, the working conditions are extremely complex, drill pipe under tension, pressure, bending, torsion and unbalanced impact load stress, but also by mud, rock wear, therefore, the requirements of pipe must have enough strength, hardness, wear resistance and impact toughness, Steel pipe with steel “DZ” (geological Chinese phonetic alphabet) plus a number on behalf of steel yield point, commonly used steel number DZ45 45MnB, 50Mn; 40Mn2, 40Mn2Si of DZ50; 40Mn2Mo, 40MnVB of DZ55; 40MnMoB for DZ60 and 27MnMoVB for DZ65. Steel pipes are delivered in a heat treated state. Petroleum cracking pipe: Seamless pipe for furnace tube, heat exchanger tube and pipeline of petroleum refinery. Commonly used high quality carbon steel (10, 20), alloy steel (12CrMo, 15CrMo), heat resistant steel (12Cr2Mo, 15Cr5Mo), stainless steel (1Cr18Ni9, 1Cr18Ni9Ti) manufacturing. In addition TO OBTAINING CHEMICAL COMPOSITION and MECHANICAL properties OF steel TUBES, IT is NECESSARY to ENSURE water pressure, flattening, flaring, surface quality and NONdestructive inspection. Steel pipes are delivered under heat treatment. 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 structure parts, in addition to should ensure chemical composition and mechanical properties, where used to bear fluid pressure steel pipe to ensure that the hydraulic test qualified. All kinds of special steel pipes should be guaranteed according to the specified conditions.