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Basic Knowledge of Steel Pipes
Release time:
2025-01-09
Steel pipes are hollow long steel materials, widely used as pipelines for transporting fluids such as oil, natural gas, water, gas, steam, etc. Additionally, they are lighter in weight when the bending and torsional strength are the same, so they are also widely used in manufacturing mechanical parts and engineering structures, and are often used to produce various conventional weapons, gun barrels, shells, etc.
Classification of steel pipes: Steel pipes are divided into 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, with round steel pipes being the most widely used, but there are also some square, rectangular, semicircular, hexagonal, equilateral triangular, octagonal, and other special-shaped steel pipes.
Steel pipes that bear fluid pressure must undergo hydraulic testing to check their pressure resistance and quality. They are considered qualified if there is no leakage, wetting, or expansion under the specified pressure. Some steel pipes also need to undergo edge rolling tests, expansion tests, flattening tests, etc., according to standards or customer requirements.
Seamless steel pipes: Seamless steel pipes are made from steel ingots or solid pipe blanks that are perforated to form a rough pipe, which is then made through hot rolling, cold rolling, or cold drawing. The specifications of seamless steel pipes are expressed in terms of outer diameter * wall thickness in millimeters. Seamless steel pipes are divided into hot-rolled and cold-rolled (drawn) 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 types of steel pipes.
Cold-rolled (drawn) seamless steel pipes, in addition to being 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 steel pipes, and other 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, with a wall thickness of 2.5-75mm; the outer diameter of cold-rolled seamless steel pipes can reach 6mm, with a wall thickness of up to 0.25mm, and thin-walled pipes can have an outer diameter of 5mm with a wall thickness of less than 0.25mm. Cold-rolled pipes have higher dimensional accuracy than hot-rolled pipes.
Generally used seamless steel pipes are made from excellent carbon structural steels such as (10, 20, 35, 45) and low alloy structural steels like 16Mn, 5MnV, or from alloy steels like (40Cr, 30CrMnSi, 45Mn2, 40MnB). Seamless pipes made from low carbon steels (10, 20) are mainly used for fluid transport pipelines. Seamless pipes made from medium carbon steels (45, 40Cr) are used to manufacture mechanical parts, such as load-bearing parts for automobiles and tractors.
Generally used seamless steel pipes must ensure strength and pass flattening tests. Hot-rolled steel pipes are delivered in a hot-rolled state or heat-treated state; cold-rolled pipes are delivered in a 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 for locomotive boilers, large smoke pipes, small smoke pipes, and arch brick pipes, etc. Low and medium pressure boiler seamless steel pipes made from excellent carbon structural steel are mainly manufactured from (10, 20) steel. In addition to ensuring chemical composition and mechanical properties, they must undergo water pressure tests, edge rolling, expansion, and flattening tests. Hot-rolled pipes are delivered in a hot-rolled state, while cold-rolled (drawn) pipes are delivered in a heat-treated state.
High pressure boiler steel pipes: Mainly used to manufacture steam boiler pipes for high pressure and above, made from excellent carbon structural steel, alloy structural steel, and stainless heat-resistant steel seamless pipes. These boiler pipes often work under high temperature and high pressure, and the pipes are subject to oxidation and corrosion under the action of high-temperature flue gas and water vapor. Therefore, the steel pipes are required to have high durability strength, high oxidation resistance, and good structural stability. The steel grades include excellent carbon structural steel grades (20G, 20MnG, 25MnG); alloy structural steel grades (15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB); and commonly used heat-resistant stainless steel (1Cr18Ni9, 1Cr18Ni11Nb). In addition to ensuring chemical composition and mechanical properties, each steel pipe must undergo water pressure tests, expansion, and flattening tests. The steel pipes are delivered in a heat-treated state. Additionally, there are certain requirements for the microstructure, grain size, and decarburization layer of the finished steel pipes.
Seamless steel pipes for geological drilling and petroleum drilling: Used to explore underground rock structure, groundwater, oil, natural gas, and mineral resources, utilizing drilling rigs to bore wells. Oil and natural gas extraction cannot be separated from drilling, and seamless steel pipes for geological drilling and petroleum drilling are the main tools for drilling, mainly including core outer pipes, core inner pipes, casings, drill rods, etc. Since drilling pipes must work at depths of several thousand meters, the working conditions are extremely complex. Drill rods bear tensile, compressive, bending, twisting, and uneven impact loads, and are also subject to wear from mud and rock. Therefore, the pipes must have sufficient strength, hardness, wear resistance, and impact toughness. The steel used for the pipes is represented by "DZ" (the pinyin initials for geology) followed by a number representing the steel yield point. Commonly used steel grades include DZ45 (45MnB, 50Mn); DZ50 (40Mn2, 40Mn2Si); DZ55 (40Mn2Mo, 40MnVB); DZ60 (40MnMoB); DZ65 (27MnMoVB). The steel pipes are delivered in a heat-treated state.
Petroleum cracking pipes: Used for furnace pipes, heat exchanger pipes, and seamless pipes in oil refineries. Commonly made from excellent 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, the pipes must also pass water pressure, flattening, expansion tests, and meet surface quality and non-destructive testing requirements. The pipes are delivered in a heat-treated state.
Stainless steel pipes: Made from various stainless steels that are hot-rolled or cold-rolled, widely used in pipelines for petroleum, chemical equipment, and various stainless steel structural parts. In addition to ensuring chemical composition and mechanical properties, any steel pipe used to bear fluid pressure must pass water pressure tests. Various special steel pipes must meet specified conditions.
Welded steel pipes: Also known as welded pipes, are made from steel plates or steel strips that are bent into shape and then welded.
Divided into three types based on manufacturing processes: straight seam resistance welded pipes (ERW), spiral submerged arc welded pipes (SSAW), and straight seam submerged arc welded pipes (UOE).
According to their use, they can be divided into general welded pipes, galvanized welded pipes, oxygen-blown welded pipes, wire casing, metric welded pipes, roller pipes, deep well pump pipes, automotive pipes, transformer pipes, electric welded thin-walled pipes, electric welded special-shaped pipes, and spiral welded pipes.
General welded pipes: General welded pipes are used to transport low-pressure fluids. Made from (Q195A, Q215A, Q235A) steel.
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