I. Definition and Classification of Steel Pipes
Steel pipes are hollow, long strips of steel widely used for conveying fluids such as oil, natural gas, water, coal gas, and steam. Furthermore, due to their light weight, while maintaining the same bending and torsional strength, they are also widely used in the manufacture of mechanical parts and engineering structures. They are also commonly used in the production of various conventional weapons, gun barrels, and artillery shells.
Steel Pipe Classification: Steel pipes are divided into two categories: seamless steel pipes and welded steel pipes (seamless steel pipes). Based on cross-sectional shape, they can be divided into round pipes and special-shaped pipes. Round steel pipes are widely used, but some special-shaped steel pipes, such as square, rectangular, semicircular, hexagonal, equilateral triangle, and octagonal, are also available. Steel pipes subject to fluid pressure must undergo hydraulic testing to verify their pressure resistance and quality. Acceptance is determined by the absence of leakage, wetting, or expansion under the specified pressure. Some steel pipes also undergo curling, flaring, and flattening tests, depending on standards or customer requirements.
Seamless steel pipe: Seamless steel pipe is made by perforating steel ingots or solid billets into rough tubes, and then hot-rolling, cold-rolling, or cold-drawing. The specifications of seamless steel pipe are expressed as outer diameter x wall thickness in millimeters. Seamless steel pipe is divided into hot-rolled and cold-rolled (drawn) 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. Cold-rolled (drawn) seamless steel pipe, in addition to general steel pipe, low- and medium-pressure boiler steel pipe, high-pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, and other steel pipes, also includes carbon thin-walled steel pipe, alloy thin-walled steel pipe, stainless thin-walled steel pipe, and special-shaped steel pipe. Hot-rolled seamless pipes generally have an outer diameter greater than 32mm and a wall thickness of 2.5-75mm. Cold-rolled seamless pipes can have an outer diameter up to 6mm and a wall thickness down to 0.25mm. Thin-walled pipes can have an outer diameter up to 5mm and a wall thickness less than 0.25mm. Cold rolling offers higher dimensional accuracy than hot rolling. Common seamless steel pipes are hot-rolled or cold-rolled from high-quality carbon steels such as 10, 20, 30, 35, and 45, low-alloy structural steels such as 16Mn and 5MnV, or alloy steels such as 40Cr, 30CrMnSi, 45Mn2, and 40MnB. Seamless pipes made from low-carbon steels such as 10 and 20 are primarily used for fluid transport piping. Seamless pipes made from medium-carbon steels such as 45 and 40Cr are used to manufacture mechanical parts, such as load-bearing components in automobiles and tractors. Generally, seamless steel pipes must meet strength and flattening tests. Hot-rolled steel pipes are delivered in the hot-rolled or heat-treated state; cold-rolled steel pipes are delivered in the hot-rolled or heat-treated state.
II. Definition and Classification of Steel Pipes
Seamless Steel Pipes for Low and Medium Pressure Boilers: Used in the manufacture of various low and medium pressure boilers, superheated steam pipes, boiling water pipes, water-cooled wall pipes, and locomotive boiler superheated steam pipes, large and small flue pipes, and arch brick pipes. These seamless steel pipes are hot-rolled or cold-rolled (drawn) from high-quality carbon structural steel. Primarily manufactured from No. 10 and No. 20 steel, these pipes undergo hydraulic pressure testing, curling, flaring, and flattening tests in addition to ensuring chemical composition and mechanical properties. Hot-rolled pipes are delivered in the hot-rolled state, while cold-rolled (drawn) pipes are delivered in the heat-treated state.
High-pressure boiler steel pipes are primarily used to manufacture seamless pipes made of high-quality carbon structural steel, alloy structural steel, and stainless heat-resistant steel for steam boilers operating at high pressures and above. These boiler pipes operate under high temperatures and pressures. Oxidation and corrosion can occur in the presence of high-temperature flue gas and steam, requiring the pipes to possess high endurance strength, high oxidation resistance, and excellent structural stability. Steel grades used include: 20G, 20MnG, and 25MnG.
Alloy structural steels include: 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, and 12Cr3MoVSiTiB.
Common stainless heat-resistant steels include: 1Cr18Ni9 and 1Cr18Ni11Nb. In addition to ensuring chemical composition and mechanical properties, each high-pressure boiler pipe undergoes hydrostatic testing, expansion, and flattening tests. The pipes are delivered in a heat-treated state. In addition, certain requirements are placed on the microstructure, grain size, and decarburized layer of the finished steel pipe. Seamless steel pipe for geological drilling and oil drilling control: Drilling rigs are used to drill wells to explore underground rock structure, groundwater, oil, natural gas, and mineral resources. Oil and natural gas extraction relies heavily on well drilling, and geological drilling control…
Seamless steel pipe for oil drilling is the primary drilling equipment, primarily consisting of core outer tubes, core inner tubes, casing, and drill pipe. Because drilling pipes penetrate thousands of meters into the earth’s strata, operating conditions are extremely complex. Drill pipes are subjected to stresses such as tension, compression, bending, torsion, and unbalanced impact loads, as well as abrasion from mud and rock. Therefore, the pipes must possess sufficient strength, hardness, wear resistance, and impact toughness. Steel grades used for pipes are designated by “DZ” (the Chinese phonetic abbreviation for geology) followed by a number representing the yield point. Commonly used steel grades include DZ45 (45MnB, 50Mn); DZ50 (40Mn2, 40Mn2Si); DZ55 (40Mn2Mo, 40MnVB); DZ60 (40MnMoB); and DZ65 (27MnMoVB). All steel pipes are delivered in the heat-treated state.
Petroleum cracking pipes: Seamless pipes used for furnace tubes, heat exchanger tubes, and pipelines in oil refineries. Commonly manufactured from high-quality carbon steel (10.20), alloy steel (12CrMo, 15CrMo), heat-resistant steel (12Cr2Mo, 15Cr5Mo), and stainless steel (1Cr18Ni9, 1Cr18Ni9Ti). In addition to verifying chemical composition and various mechanical properties, steel pipes must also undergo hydraulic pressure, flattening, and flaring tests, as well as surface quality and non-destructive testing. Steel pipes are delivered in the heat-treated state.
Stainless steel pipes: Made from various hot-rolled and cold-rolled stainless steels, they are widely used in petroleum and chemical equipment piping and various stainless steel structural components. In addition to ensuring chemical composition and mechanical properties, all steel pipes designed to withstand fluid pressure must pass hydraulic pressure testing. Various specialized steel pipes must meet specified conditions. Welded steel pipes: Also called welded pipes, they are made from steel plates or strips that are bent and then welded. Based on the weld seam, they are categorized as straight seam welded pipes and spiral welded pipes. According to their application, they are categorized into general welded pipe, galvanized welded pipe, oxygen-blown welded pipe, wire conduit, metric welded pipe, roller pipe, deep-well pump pipe, automotive pipe, transformer pipe, electric-welded thin-walled pipe, electric-welded special-shaped pipe, and spiral welded pipe. General welded pipe: General welded pipe is used to transport low-pressure fluids. It is made of Q195A, Q215A, and Q235A steel.
It can also be made of other mild steels that are easily welded. Steel pipes undergo water pressure, bending, and flattening tests, and have certain surface quality requirements. Delivery lengths are typically 4-10 meters, and custom lengths (or multiple lengths) are often required. Welded pipe specifications are expressed in nominal diameter (millimeters or inches). The nominal diameter may differ from the actual diameter. Welded pipes are available in two types: standard steel pipe and thickened steel pipe, depending on the specified wall thickness. Steel pipes are also available in two types: threaded and non-threaded, depending on the end type.
III. Definition and Classification of Steel Pipes
Galvanized Steel Pipe: To improve corrosion resistance, ordinary steel pipe (black pipe) is galvanized. Galvanized steel pipe is divided into hot-dip galvanizing and electrogalvanizing. Hot-dip galvanizing has a thicker galvanizing layer, while electrogalvanizing is less expensive.
Oxygen-Blowing Welded Pipe: Used as oxygen blowing pipe in steelmaking, it is generally a small-diameter welded steel pipe with eight specifications ranging from 3/8 inch to 2 inches. It is made of 08, 10, 15, 20 or Q195-Q235 steel strip. Some are aluminized for corrosion protection.
Wire Sleeving: Also ordinary carbon steel electric-welded pipe, it is used in concrete and various structural power distribution projects. Common nominal diameters range from 13-76mm. Wire Sleeving has a thinner wall and is often coated or galvanized before use. Cold bending tests are required.
Metric welded pipe: This is a seamless steel pipe with specifications expressed as outer diameter x wall thickness in millimeters. It is made by hot strip welding, cold strip welding, or hot strip welding followed by cold drawing of ordinary carbon steel, high-quality carbon steel, or general-purpose low-alloy steel. Metric welded pipe is available in both general-purpose and thin-walled versions. These are commonly used as structural components, such as drive shafts, or for conveying fluids. Thin-walled pipes are used in furniture, lighting, and other applications. Steel strength and bend tests must be ensured.
Roller pipe: This is an electric-welded steel pipe used for belt conveyor rollers. It is generally made of Q215, Q235A, B, and 20 steel, with diameters ranging from 63.5 to 219.0 mm. Requirements are in place for curvature, perpendicularity of the end face to the centerline, and ovality. Water pressure and flattening tests are generally performed.
Transformer pipe: This is used in the manufacture of transformer radiator pipes and other heat exchangers. It is made of ordinary carbon steel and requires flattening, flaring, bending, and hydraulic pressure testing. Steel pipes are delivered in fixed or multiple lengths, with certain requirements for curvature.
Special-shaped pipes: Square, rectangular, and cap-shaped pipes, as well as hollow plastic steel doors and windows, are welded from ordinary carbon structural steel and 16Mn steel strip.
Special-shaped pipes are primarily used for agricultural machinery components, steel windows and doors, and more. Electric-welded thin-walled pipes: Primarily used in furniture, toys, and lamps. In recent years, thin-walled pipes made from stainless steel strip have become increasingly popular, including high-end furniture, decoration, and fences.
Spiral welded pipes: Low-carbon structural steel or low-alloy structural steel strip is rolled into a tube blank at a specific spiral angle (called a forming angle) and then welded together. This allows for the production of large-diameter steel pipes from narrower strips. Spiral welded pipes are primarily used in oil and natural gas pipelines. Specifications are expressed as outer diameter x wall thickness. Spiral welded pipes are available in single-sided and double-sided welded versions. The welds must meet requirements for hydrostatic testing, tensile strength, and cold bending properties.
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