Steel pipes are hollow, elongated materials widely used as conduits for the transmission of fluids such as oil, natural gas, water, coal gas and steam. With equivalent bending and torsional strength, they are lighter and therefore commonly used in manufacturing mechanical parts and engineering structures. They are also frequently employed in the production of conventional weaponry, gun barrels and artillery shells.
Steel pipes can be divided into two main categories: seamless and welded (seamed) pipes.
Based on their cross-sectional shapes, they can be classified into circular and special-shaped tubes. Although circular steel tubes are the most widely used, other shapes such as square, rectangular, semicircular, hexagonal, equilateral triangular and octagonal are also available.
All steel pipes that support fluid pressure are subjected to hydraulic tests to verify their pressure resistance and quality. To be approved, they must not leak, wet or expand under the specified pressure. Some pipes also undergo flanging, flaring, or flattening tests based on specific standards or requirements.
Seamless steel tubes are made by punching a steel ingot or solid tube blank to create a capillary tube, which is then hot rolled, cold rolled, or cold drawn. The specifications of seamless steel pipes are indicated by the outer diameter and wall thickness in millimeters. They can be divided into hot-rolled and cold-rolled (drawn) seamless steel tubes.
Hot rolled seamless steel pipes come in various types, including general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes , oil cracking pipes, geological steel pipes and others.
Cold-rolled (drawn) seamless steel tubes in addition to the types mentioned above, also include carbon thin-wall steel tubes, alloy thin-wall steel tubes, thin-wall stainless steel tubes and shape steel tubes. Special.
Hot rolled seamless tubes generally have an outer diameter greater than 32mm and a wall thickness between 2.5-7.5mm. Cold rolled seamless steel tubes can have an outer diameter as small as 6mm, a wall thickness as thin as 0.25mm, and thin-walled tubes can have an outer diameter as small as 5mm with a wall thickness less than 0.25 mm. The dimensional accuracy of cold-rolled tubes is higher than that of hot-rolled tubes.
Standard seamless steel pipes are typically made from high-quality carbon structural steels such as 10, 20, 30, 35, 45, or low-alloy structural steels such as 16Mn, 5MnV, or alloy structural steels such as 40Cr, 30CrMnSi , 45Mn2, 40MnB through hot – rolling or cold rolling. Seamless pipes made from low carbon steels such as 10, 20 are mainly used for fluid transportation pipelines. Meanwhile, seamless tubes made from medium carbon steels such as 45, 40Cr are used in manufacturing mechanical parts such as those found in cars and tractors.
Seamless steel tubes are generally used, with an emphasis on ensuring resistance and flatness tests. Hot-rolled steel pipes are delivered in a hot-rolled or heat-treated state, while cold-rolled pipes are delivered in a heat-treated state. Seamless steel tubes for low to medium pressure boilers are used to manufacture 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 pipes, small smoke pipes and arched brick pipes.
High-quality carbon structural steel hot-rolled or cold-rolled (marked) seamless steel pipes are mainly manufactured from 10, 20 steel. In addition to ensuring the chemical composition and mechanical properties, water pressure testing is required, edge rolling, flaring and flatness testing. Hot-rolled tubes are delivered in a hot-rolled state, and cold-rolled (dial) tubes are delivered in a heat-treated state.
High pressure boiler steel tubes are mainly used to manufacture high quality carbon structural steel, alloy structural steel and heat resistant seamless stainless steel tubes for piping of high pressure steam boilers and above . These boiler tubes generally operate under high temperature and pressure. Pipes undergo oxidation and corrosion under the action of high-temperature combustion gases and steam, therefore, they require high strength, high oxidation resistance and good structural stability.
Steel types used include 20G, 20MnG, 25MnG high-quality carbon structural steel; 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB structural alloy steel; and commonly used heat-resistant stainless steel 1Cr18Ni9, 1Cr18Ni11Nb.
In addition to ensuring chemical composition and mechanical properties, high-pressure boiler tubes must undergo root water pressure tests, as well as expansion and flatness tests. Steel pipes are delivered in a heat-treated state. In addition, the finished steel pipe's microstructure, grain size and decarburization layer also have certain requirements.
Seamless steel pipes are used for geological drilling and oil drilling; To explore the structure of the underground rock layer, groundwater, oil, natural gas and mineral resources, wells are drilled with drilling machines. Oil and natural gas extraction cannot be separated from drilling. Seamless steel pipes used for geological drilling and petroleum exploration are the main drilling equipment, including outer tubes for core drilling, inner tubes for core drilling, casings and drill rods. Drill pipes must work at depths of several kilometers, in extremely complex conditions. The drill rod withstands tension, compression, bending, twisting and unbalanced impact loads, as well as abrasion from mud and rock.
Therefore, the pipe material must have sufficient strength, hardness, wear resistance and impact resistance. The steel used for the pipe is represented by “DZ” (the Chinese pinyin initials for geology) plus numbers representing the yield strength of the steel. Commonly used steel numbers are 45MnB, 50Mn of DZ45; 40Mn2, 40Mn2Si from DZ50; 40Mn2Mo, 40MnVB from DZ55; 40MnMoB from DZ60, 27MnMoVB from DZ65. The steel tubes are all delivered in a heat treated state.
Petroleum cracking tubes: These are seamless tubes used in furnace tubes, heat exchanger tubes and pipelines in petroleum refineries. They are commonly made of high-quality carbon steel (10, 20), alloy steel (12CrMo, 15CrMo), heat-resistant steel (12Cr2Mo, 15Cr5Mo) and stainless steel (1Cr18Ni9, 1Cr18Ni9Ti). In addition to checking the chemical composition and various mechanical properties of steel pipes, it is also necessary to ensure testing for water pressure, flattening, widening, as well as checking the surface quality and non-destructive inspection. Steel pipes are delivered in a heat-treated state.
Stainless steel tubes: These are hot-rolled and cold-rolled stainless steel tubes made from various types of stainless steel. 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, any steel pipes used to withstand fluid pressure must pass water pressure tests. Various special steel pipes must meet certain prescribed conditions.
Welded steel tubes: Also known as welded tubes, they are made by forming steel plates or strips and then welding them together. They are divided into straight seam welded pipes and spiral welded pipes based on the shape of the welding seam. They are further divided into general welded pipes, galvanized welded pipes, oxygen blow pipes, wire casing pipes, metric welded pipes, roller pipes, deep well pump pipes, automotive pipes, transformer pipes, electrically welded thin walls, electrically welded shaped tubes. and spiral welded pipes, based on your application.
General welded pipes: These pipes are used to transport low pressure fluids. They are made of Q195A, Q215A, Q235A steel. Other types of easily weldable mild steel can also be used. Water pressure, bending and flattening tests are required for these pipes, and there are specific requirements for surface quality. They are generally delivered in lengths of 4 to 10 m, often requiring fixed length (or double length) delivery.
The specifications of welded pipes are expressed in nominal diameters (in millimeters or inches), which differ from the actual size. Welded pipes have two types based on wall thickness: normal steel pipes and thickened steel pipes, and two types based on the shape of the pipe end: threaded and non-threaded.
As steel pipe welding technology continues to improve and processing becomes simpler, welded pipes are now replacing some seamless pipes. Welded steel tubes can now be produced in sizes greater than 219 mm (8 inches).
Galvanized steel pipe: To increase the corrosion resistance of steel pipes, general steel pipes (black pipes) are galvanized. Galvanized steel pipes come in two types: hot-dip galvanized and electro-galvanized. Hot-dip galvanizing provides a thicker coating, while electro-galvanizing is more economical.
Oxygen blowing pipe: Used for oxygen blowing in steelmaking, typically small diameter welded steel pipes, with sizes ranging from 3/8 to 2 inches. They are manufactured with 08, 10, 15, 20 or Q195-Q235 steel strips. To prevent corrosion, some are treated with aluminum infiltration.
Electrical Conduit: This is a standard carbon steel welded pipe used in concrete and various structural power distribution projects. The common nominal diameter ranges from 13 to 76 mm. Conduit walls are thin, usually coated or galvanized for use, and need to pass a cold bending test.
Metric welded pipe: This type of welded steel pipe is indicated in the form of seamless pipe specifications, represented by outer diameter * wall thickness in millimeters. It is made of common carbon steel, high-quality carbon steel or hot or cold strip welding of general low alloy steel, or after hot strip welding, it is produced by cold drawing method.
Metric welded pipe is divided into general and thin-walled types. The general type is used as structural parts, such as drive shafts, or for transporting fluids. Thin-walled tubes are used in the manufacture of furniture, lamps, etc., ensuring the strength of the steel tube and passing the bending test.
Roller tube: Refers to the welded steel tube used for belt conveyor rollers, generally made of Q215 steel, Q235A steel, B steel and 20 steel, with diameters of 63.5-219.0 mm. The degree of pipe curvature, perpendicularity of the end face to the center line and ovality are subject to specific requirements, generally subjected to hydraulic and flattening tests.
Transformer tube: This type of tube is used to manufacture heat dissipation tubes of transformers and other heat exchangers. It is made from common carbon steel and must pass flattening, flaring, bending and hydraulic tests.
Steel tubes are delivered in fixed or multiple lengths, with specific requirements for the degree of curvature of the steel tube. Special-shaped tube: These are square tubes, rectangular tubes, cap-shaped tubes, hollow rubber steel doors and window tubes welded from ordinary carbon structural steel and 16Mn steel strips. They are mainly used as agricultural machinery parts, steel windows and doors, etc.
Thin-wall welded tube: Mainly used for manufacturing furniture, toys, lamps, etc. In recent years, thin-walled tubes made of stainless steel strips have found wide applications in high-end furniture, decoration, railings, etc.
Spiral welded pipe: This is created by rolling strips of low-carbon structural steel or low-alloy structural steel at a certain helical angle (called forming angle) onto a pipe blank and then welding the pipe seam . Allows the production of large diameter steel tubes using narrower steel strips. Spiral welded pipes are mainly used for oil and natural gas transportation pipelines, with specifications represented by outer diameter * wall thickness. Spiral welded pipes come in one-sided and double-sided welding, and the pipe must ensure that hydraulic testing, weld tensile strength and cold bending performance are in line with regulations.
I. Classification of Tubular Materials
1. Based on production method:
(1) Seamless tubes – hot rolled tubes, cold rolled tubes, cold drawn tubes, extruded tubes, pushed tubes.
(2) Welded pipes:
- (a) By process – arc welded pipes, resistance welded pipes (high frequency, low frequency), gas welded pipes, furnace welded pipes.
- (b) By seam welding – straight seam welded tubes, spiral welded tubes.
2. Based on the cross-sectional shape:
(1) Simple cross-section steel tubes – circular steel tubes, square steel tubes, elliptical steel tubes, triangular steel tubes, hexagonal steel tubes, diamond steel tubes, octagonal steel tubes, semicircular steel tubes , others.
(2) Complex cross-section steel tubes – unequal hexagonal steel tubes, five-petal plum blossom-shaped steel tubes, double convex steel tubes, double concave steel tubes, plum seed-shaped steel tubes melon, tapered steel tubes, corrugated steel tubes, shell steel tubes, others.
3. Based on wall thickness:
Thin-walled steel tubes, thick-walled steel tubes.
4. Based on Purpose:
Steel pipes for pipelines, steel pipes for thermal equipment, steel pipes for mechanical industry, steel pipes for petroleum and geological drilling, steel pipes for containers, steel pipes for chemical industry, steel pipes for special purposes, others .
II. Seamless Steel Tubes
Seamless steel tubes are elongated steel materials with a hollow cross-section and no seams on their periphery. These pipes, due to their hollow cross-section, are widely used in fluid transmission pipelines, such as pipes for transporting petroleum, natural gas, coal gas, water and certain solid materials.
Compared with solid steel materials such as round steel, seamless steel pipes are lighter while maintaining the same bending and torsional strength, making them economical cross-section steel materials. They are widely used in the manufacture of structural components and mechanical parts such as oil drilling rods, automobile drive shafts, bicycle frames, and steel scaffolding used in construction.
Manufacturing annular parts from steel tubes improves material utilization, simplifies the manufacturing process, saves materials and reduces processing time. This method is now widely used in applications such as bearing rings and jacks. Steel tubes are also indispensable materials for various conventional weapons, and gun barrels and cannons are manufactured from them.
Steel tubes can be categorized into round and special-shaped tubes based on cross-sectional area. Since the circular area is the largest under the condition of equal circumference, round tubes can transport more fluid. Furthermore, force is distributed more evenly when a pipe with a circular cross-section supports internal or external radial pressure, therefore most steel pipes are round.
However, round tubes have certain limitations. For example, in the case of flat bending, square or rectangular tubes have greater resistance to bending.
Therefore, square or rectangular tubes are commonly used in the skeletal structures of agricultural machinery and steel and wooden furniture. Depending on the application, special shaped steel tubes and other cross-sectional shapes are also required.
1. Seamless steel tubes for structural purposes (GB/T8162-1999) are used for general structures and mechanical structures.
2. Seamless steel pipes for fluid transportation (GB/T8163-1999) are commonly used for transportation of water, oil, gas and other fluids.
3. Seamless steel tubes for low and medium pressure boilers (GB3087-1999) are employed in the manufacture of various structural components in low and medium pressure boilers, including superheated steam tubes, boiling water tubes, superheated steam tubes of locomotive boilers, large ducts, small ducts and arched brick tubes. These tubes are made from high-quality carbon structural steel through hot rolling or cold drawing (rolling).
4. Seamless steel tubes for high pressure boilers (GB5310-1995) are used in manufacturing heating surfaces of water tube boilers operating under high pressures and above. These pipes are made up of high quality carbon steel, alloy steel and heat resistant stainless steel.
5. High pressure seamless steel pipes for fertilizer equipment (GB6479-86) are suitable for chemical equipment and pipelines operating in a temperature range of -40 to 400°C and a pressure of 10 to 30Ma. These tubes are made of high quality carbon structural steel and alloy steel.
6. Petroleum cracking seamless steel tubes (GB9948-88) are suitable for furnace tubes, heat exchangers and pipelines in petroleum refineries.
7. Geological drilling steel pipes (YB235-70) are supplied for core drilling by geological departments. Depending on the application, these pipes can be divided into drill rods, drill heads, core pipes, casing pipes and precipitation pipes.
8. Seamless steel pipes for diamond core drilling (GB3423-82) are used for drill rods, core rods and casings in diamond core drilling.
9. Oil drilling pipes (YB528-65) are seamless steel pipes with thickened ends used for oil drilling. These pipes come in two types: threaded and unthreaded. Threaded pipes are connected to a joint, while non-threaded pipes are connected by welding to the tool joint.
10. Ship Seamless Carbon Steel Pipes (GB5213-85) are used in manufacturing Class I pressure pipe systems, Class II pressure pipe systems, boilers and superheaters. Carbon steel seamless tubes have a maximum working temperature of 450°C, while alloy steel seamless tubes can withstand temperatures above 450°C.
11. Seamless Steel Tubes for Automobile Half Shaft Housings (GB3088-82) are hot rolled seamless tubes made of high quality carbon structural steel and alloy structural steel, used to manufacture half shaft housings of automobiles and transmission shaft housings.
12. High pressure fuel pipes for diesel engines (GB3093-86) are cold drawn seamless steel pipes used to make the injection system of diesel engines.
13. Precision Seamless Steel Tubes with Inner Diameter for Hydraulic and Pneumatic Cylinders (GB8713-88) are cold drawn or cold rolled precision seamless steel tubes with precise inner diameter sizes for manufacturing hydraulic and pneumatic cylinders.
14. Cold drawn or cold rolled precision seamless steel tubes (GB3639-83) are used for mechanical structures and hydraulic equipment, featuring high dimensional accuracy and good surface smoothness. Using precision seamless steel tubes for mechanical structures or hydraulic equipment can significantly save machining time, improve material utilization and improve product quality.
15. Stainless steel seamless tubes for structures (GB/T14975-1994) are hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless tubes made of stainless steel, widely used in chemical, petroleum, textile , medical, food, machinery and other industries for piping, structural components and corrosion-resistant parts.
16. Stainless steel seamless tubes for fluid transport (GB/T14976-1994) are hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless tubes made of stainless steel, intended for the transport of fluids.
17. Special-shaped seamless steel tubes refer to seamless steel tubes with shapes other than round. Depending on the different dimensions of the cross-sectional shape, they are divided into seamless steel tubes with equal wall thickness (Code D), unequal wall thickness (Code BD) and variable diameter (Code BJ). Special shaped seamless steel tubes are widely used in various structural components, tools and mechanical parts. Compared to round tubes, specially shaped tubes generally have greater moments of inertia and section modulus, providing greater resistance to bending and torsion, significantly reducing structural weight and saving steel.
III. Welded Steel Pipes
Welded steel pipes, also known as welded pipes, are made by rolling steel plates or strips and then welding them together. The welded steel pipe production process is simple, efficient and comes in a variety of specifications with minimal equipment requirements. However, its strength is generally lower than that of seamless steel pipes.
Since the 1930s, with the rapid development of high-quality steel strip rolling production and advances in welding and inspection technology, the quality of weld beads has continuously improved.
The variety and specifications of welded steel pipes are increasing and replacing seamless steel pipes in an increasing number of fields. Welded steel pipes are categorized into straight seam welded pipes and spiral welded pipes based on the shape of the weld seam.
The production process of straight seam welded pipes is simple, efficient and economical, resulting in rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. They can be produced from narrower billets to obtain welded tubes of larger diameter, and welded tubes of different diameters can be produced from billets of the same width.
However, compared with straight seam pipes of the same length, the length of the weld seam increases by 30-100% and the production speed is slower. Therefore, smaller diameter welded pipes mainly use straight seam welding, while larger diameter welded pipes mainly use spiral welding.
1. Welded steel pipes for low pressure fluid transmission (GB/T3092-1993), also known as general welded pipes or colloquially as black pipes, are used to transport water, gas, air, oil and steam. heating generally under low pressure, and for other purposes. The wall thickness of the steel pipe varies between normal steel pipes and thickened steel pipes, and the end of the pipe can be threadless (smooth pipe) or threaded. Steel pipe specifications are given in nominal diameter (mm), which is an approximate value of the internal diameter. They are commonly expressed in inches, such as 1 1/2, etc. In addition to being used directly for fluid transmission, these pipes are also widely used as base pipes for welded galvanized steel pipes for low-pressure fluid transmission.
2. Galvanized welded steel pipes for transmission of low pressure fluids (GB/T3091-1993), also known as galvanized electric welding steel pipes or colloquially as white pipes, are hot-dip galvanized (furnace) welded steel pipes or electric welded) used for transporting water, gas, air, oil, heating steam, hot water and other generally low-pressure fluids. The pipe wall thickness varies between normal galvanized steel pipes and thickened galvanized steel pipes, and the end of the pipe can be unthreaded or threaded. Pipe specifications are given in nominal diameter (mm), which is an approximate value of the internal diameter. They are commonly expressed in inches, such as 1 1/2, etc.
3. Carbon steel common electrical conduit (GB3640-88) is a steel pipe used for wire protection in industrial and civil buildings, machinery and equipment installation and other electrical installation projects.
4. Straight seam electric resistance welded pipes (YB242-63) are steel pipes with the welding seam parallel to the longitudinal direction of the pipe. They are generally divided into metric welded steel pipes, thin-walled electrically welded pipes, transformer cooling oil pipes and so on.
5. Spiral Submerged Arc Welded Steel Pipes for Pressure Fluid Transmission (SY5036-83) are steel pipes made from coils of hot-rolled steel strips as billet, formed by normal temperature spiral shaping and welded by welding by double-sided submerged arc. These pipes have strong pressure-bearing ability, excellent welding performance, and are safe and reliable after rigorous scientific testing. With their large diameter, they offer high transmission efficiency and can save investments in pipe laying. They are mainly used to transport oil and natural gas.
6. High-frequency welded spiral seam steel pipes (SY5038-83) for pressure fluid transmission are manufactured from hot-rolled steel strip coils. They are formed into spiral shapes at room temperature and welded using high-frequency overlap welding. These tubes, designed for the transmission of pressurized fluids, are resistant and plastic at high pressure, facilitating welding and modeling processes. After undergoing rigorous scientific testing, they guarantee safe and reliable use. Its large diameter increases transmission efficiency and can reduce pipeline construction costs. They are mainly used to install pipelines for transporting oil and natural gas.
7. Spiral seam submerged arc welded steel pipes (SY5037-83) for general low pressure fluid transportation are made from hot rolled steel strip blanks that are spiral shaped at room temperature and welded using welding automatic by double-sided submerged arc or unilateral welding. These pipes are used for transporting water, gas, air and steam under general low pressure conditions.
8. Spiral seam high-frequency welded steel pipes (SY5039-83) for general low-pressure fluid transportation are produced from hot-rolled steel strip coils. These blanks are spirally formed at room temperature and welded using high-frequency welding, resulting in tubes suitable for general low-pressure fluid transport.
9. Spiral weld seam steel pipes (SY5040-83) for use in piles are also made from coils of hot-rolled steel strips. They are spiral-shaped at room temperature and welded by double-sided submerged arc or high-frequency welding. They are used in building construction structures, piers, bridges and other foundation pile applications.
4. Steel-plastic composite pipes and large diameter coated steel pipes
Steel-plastic composite pipes, using hot-dip galvanized steel pipes as the base, are manufactured by fusion and powder spraying technology, coating the inner wall (and outer wall when necessary) with plastic, resulting in excellent performance.
Compared with galvanized pipes, they have the advantages of being corrosion-resistant, rust-free, scale-free, smooth and clean, non-toxic and have a long service life.
According to tests, the service life of steel-plastic composite pipes is more than three times that of galvanized pipes. Compared to plastic pipes, they have high mechanical strength, good pressure and heat resistance. As the base is a steel tube, there are no problems with brittleness or aging. They can be widely used in water supply, gas, chemical, fluid transportation and heating projects, making them an upgraded alternative to galvanized pipes.
Its installation and use methods are essentially the same as traditional galvanized pipes, and the pipe fitting ways are identical. They can replace aluminum-plastic composite pipes in large-diameter water supply transportation, are well received by users, and have become one of the most competitive new products in the pipe market.
Coated steel pipes are made by plastic coating on large diameter spiral welded pipes and high frequency welded pipes, with a maximum pipe diameter reaching 1200mm. They can be coated with different types of plastic coatings such as polyvinyl chloride (PVC), polyethylene (PE), epoxy resin (EPOZY), etc., according to different needs.
These coatings have good adhesion, strong corrosion resistance, and can withstand strong acid, strong alkali and other chemical corrosion. They are non-toxic, non-rusting, wear-resistant, impact-resistant and have strong permeation resistance.
The tube surface is smooth, does not stick to any substances, reduces resistance during transportation, improves flow and transportation efficiency, and reduces pressure loss during transportation. The coatings do not contain solvents or leachable substances, therefore they do not contaminate the transported medium, guaranteeing the purity and hygiene of the fluid.
They can be used in cold and hot cycles alternately in the range from -40°C to +80°C, without aging or cracking, allowing use in aggressive environments such as cold regions. Large diameter coated steel pipes are widely used in water supply, natural gas, petroleum, chemicals, pharmaceuticals, telecommunications, energy, marine and other engineering fields.
