Classification and Standards of Steel Pipes

DATE：2026-05-21 14:48:51NUM：0

Classification of Steel Pipes

1. Classification by Production Method

(1) Seamless Steel Pipes—Hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, extruded pipes, and jacking pipes

(2) Welded Pipes

(a) By Process—Arc-welded pipes, resistance-welded pipes (high-frequency, low-frequency), gas-welded pipes, and furnace-welded pipes

(b) By Weld Type—Longitudinally welded pipes and spiral-welded pipes

2. Classification by Cross-Section Shape

(1) Simple-section steel pipes—round steel pipes, square steel pipes, oval steel pipes, triangular steel pipes, hexagonal steel pipes, rhombic steel pipes, octagonal steel pipes, half-round steel pipes, others

(2) Steel pipes with complex cross-sections—unequal-sided hexagonal steel pipes, five-petal plum-blossom-shaped steel pipes, double-convex steel pipes, double-concave steel pipes, seed-shaped steel pipes, conical steel pipes, corrugated steel pipes, watch case steel pipes, others

3. Classification by wall thickness—thin-walled steel pipes, thick-walled steel pipes

4. Classification by Application—Steel pipes for pipelines, steel pipes for thermal equipment, steel pipes for the machinery industry, steel pipes for petroleum and geological drilling, steel pipes for pressure vessels, steel pipes for the chemical industry, steel pipes for special applications, others.

II. Standards for Seamless Steel Pipes

A seamless steel pipe is a long steel product with a hollow cross-section and no seams along its circumference. Due to their hollow cross-section, steel pipes are extensively used as conduits for transporting fluids, such as pipelines for oil, natural gas, coal gas, water, and certain solid materials. Compared to solid steel products like round bars, steel pipes offer equivalent bending and torsional strength while being lighter in weight, making them an economical cross-sectional material. They are widely used in the manufacture of structural components and mechanical parts, such as oil drilling pipes, automotive drive shafts, bicycle frames, and steel scaffolding in construction. Using steel pipes to manufacture ring-shaped parts improves material utilization, simplifies manufacturing processes, and saves on materials and machining time. Examples include rolling bearing rings and jack sleeves, which are now widely produced using steel pipes. Steel pipes are also an indispensable material for various conventional weapons; gun barrels and cannon barrels, for instance, are manufactured from steel pipes. Steel tubes can be classified into round tubes and shaped tubes based on the shape of their cross-sectional area. Since a circle has the largest area for a given circumference, round tubes can convey more fluid. Additionally, a circular cross-section distributes stress more evenly when subjected to internal or external radial pressure; therefore, the vast majority of steel tubes are round.

However, round tubes also have certain limitations. For example, under conditions of planar bending, round tubes do not possess the same bending strength as square or rectangular tubes; consequently, square and rectangular tubes are commonly used in the frames of agricultural machinery and in steel-and-wood furniture. Depending on the specific application, seamless steel tubes with other cross-sectional shapes are also required.

1. Seamless Steel Tubes for Structural Purposes (GB/T 8162-1999) are seamless steel tubes used for general structural and mechanical applications.

2. Seamless Steel Tubes for Fluid Conveyance (GB/T 8163-1999) are general-purpose seamless steel tubes used for conveying fluids such as water, oil, and gas.

3. Seamless steel tubes for low- and medium-pressure boilers (GB 3087-1999) are high-quality carbon structural steel hot-rolled and cold-drawn (rolled) seamless steel tubes used to manufacture superheated steam tubes, boiling water tubes for various low- and medium-pressure boiler structures, as well as superheated steam tubes, large smoke tubes, small smoke tubes, and arch brick tubes for locomotive boilers.

4. Seamless Steel Pipes for High-Pressure Boilers (GB 5310-1995) are seamless steel pipes made of high-quality carbon steel, alloy steel, and stainless heat-resistant steel, used for manufacturing heat-exchanging surfaces in water-tube boilers operating at high pressure and above.

5. High-pressure seamless steel pipes for fertilizer equipment (GB6479-2000) are high-quality carbon structural steel and alloy steel seamless pipes suitable for chemical equipment and pipelines operating at temperatures ranging from -40°C to 400°C and pressures from 10 to 30 MPa.

6. Seamless Steel Pipes for Petroleum Cracking (GB9948-88) are seamless steel pipes suitable for furnace tubes, heat exchangers, and pipelines in petroleum refineries.

7. Steel Pipes for Geological Drilling (YB235-70) are steel pipes used by geological departments for core drilling; based on their application, they can be classified into drill pipes, drill collars, core tubes, casing, and sedimentation tubes, among others.

8. Seamless Steel Pipes for Diamond Core Drilling (GB3423-82) are seamless steel pipes used for drill pipes, core rods, and casing in diamond core drilling.

9. Oil Drilling Pipes (YB528-65) are seamless steel pipes with internal or external thickening at both ends, used for oil drilling. Steel pipes are classified into threaded and non-threaded types. Threaded pipes are connected using couplings, while non-threaded pipes are connected to tool joints via butt welding.

10. Seamless carbon steel pipes for ships (GB5213-85) are seamless carbon steel pipes used to manufacture Class I and Class II pressure piping systems, as well as boilers and superheaters for ships. The operating temperature of the wall of carbon steel seamless steel pipes does not exceed 450°C, while that of alloy steel seamless steel pipes exceeds 450°C.

11. Seamless steel pipes for automotive half-shaft sleeves (GB3088-82) are hot-rolled seamless steel pipes made of high-quality carbon structural steel and alloy structural steel, used for manufacturing automotive half-shaft sleeves and drive axle housing tubes.

12. High-pressure fuel lines for diesel engines (GB 3093-2002) are cold-drawn seamless steel tubes used for manufacturing high-pressure lines in diesel engine injection systems.

13. Seamless steel tubes with precision inner diameters for hydraulic and pneumatic cylinders (GB 8713-88) are cold-drawn or cold-rolled precision seamless steel tubes with precise inner diameter dimensions, used for manufacturing hydraulic and pneumatic cylinder barrels.

14. Cold-drawn or cold-rolled precision seamless steel tubes (GB 3639-2000) are cold-drawn or cold-rolled precision seamless steel tubes with high dimensional accuracy and good surface finish, used for mechanical structures and hydraulic equipment.

Selecting precision seamless steel tubes for the manufacture of mechanical structures or hydraulic equipment can significantly reduce machining time, improve material utilization, and simultaneously enhance product quality.

15. Stainless steel seamless pipes for structural use (GB/T 14975-2002) are hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless pipes made of stainless steel, widely used for corrosion-resistant piping, structural components, and parts in industries such as chemical, petroleum, light industry, textiles, medical, food, and machinery.

16. Seamless stainless steel pipes for fluid conveyance (GB/T 14976-2002) are hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless pipes made of stainless steel, used for conveying fluids.

17. Special-shaped seamless steel pipes is a general term for seamless steel pipes with cross-sectional shapes other than circular. Based on differences in cross-sectional shape and dimensions, they can be further classified into constant-wall-thickness special-shaped seamless steel pipes (designated as D), variable-wall-thickness special-shaped seamless steel pipes (designated as BD), and variable-diameter special-shaped seamless steel pipes (designated as BJ). Special-shaped seamless steel pipes are widely used in various structural components, tools, and mechanical parts. Compared to round pipes, special-shaped pipes generally have larger moments of inertia and section moduli, offering greater resistance to bending and torsion. This allows for significant reduction in structural weight and savings in steel consumption.

III. Standards for Welded Steel Pipes

Welded steel pipes, also known as welded tubes, are manufactured by rolling steel plates or strips into a cylindrical shape and then welding the seams. The production process for welded steel pipes is simple, with high production efficiency, a wide variety of specifications, and low capital requirements; however, their strength is generally lower than that of seamless steel pipes. Since the 1930s, with the rapid development of continuous rolling for high-quality steel strips and advancements in welding and inspection technologies, weld quality has continuously improved. The variety and specifications of welded steel pipes have increased significantly, and they have increasingly replaced seamless steel pipes in a growing number of applications. Welded steel pipes are classified by weld type into straight-seam welded pipes and spiral-seam welded pipes.

Straight-seam welded pipes feature a simple production process, high production efficiency, low costs, and have seen rapid development. Spiral-welded pipes generally have higher strength than straight-seam welded pipes. They allow for the production of larger-diameter pipes using narrower strip stock, and different pipe diameters can be produced using strip stock of the same width. However, compared to straight-seam pipes of the same length, the weld length increases by 30–100%, and the production speed is lower.

Therefore, small-diameter welded pipes are mostly produced using straight-seam welding, while large-diameter welded pipes are mostly produced using spiral welding.

1. Welded Steel Pipes for Low-Pressure Fluid Conveyance (GB/T 3092-1993), also known as general-purpose welded pipes or commonly referred to as “black pipes,” are used for conveying water, gas, air, oil, heating steam, and other general-purpose low-pressure fluids, as well as for other applications. These pipes are classified by wall thickness into standard-wall and heavy-wall pipes; based on end configuration, they are classified as plain-end pipes (smooth-end pipes) and threaded pipes. Pipe specifications are expressed in nominal diameter (mm), which is an approximate value of the inner diameter. It is customary to use inches for measurement, such as 1½, etc. In addition to being used directly for fluid conveyance, welded steel pipes for low-pressure fluid conveyance are also extensively used as raw material for galvanized welded steel pipes for low-pressure fluid conveyance.

2. Galvanized welded steel pipes for low-pressure fluid conveyance (GB/T 3091-1993), also known as galvanized electric-welded steel pipes and commonly referred to as “white pipes,” are hot-dip galvanized welded (furnace-welded or electric-welded) steel pipes used for conveying water, gas, air, oil, heating steam, hot water, and other general low-pressure fluids, as well as for other applications. These pipes are classified by wall thickness into standard galvanized steel pipes and heavy-wall galvanized steel pipes; by end configuration into plain-end galvanized steel pipes and threaded-end galvanized steel pipes. Pipe specifications are expressed in nominal diameter (mm), which is an approximate value of the inner diameter. Conventionally, inches are often used, such as 1½, etc.

3. Ordinary carbon steel electrical conduit (GB3640-88) is a steel pipe used to protect electrical wires in electrical installation projects for industrial and civil buildings, as well as in the installation of machinery and equipment.

4. Longitudinally welded steel pipes (YB242-63) are steel pipes in which the weld runs parallel to the longitudinal axis of the pipe. They are typically classified into metric electric welded steel pipes, thin-walled electric welded pipes, transformer cooling oil pipes, and so on.

5. Spiral-welded submerged-arc welded steel pipes for pressure fluid conveyance (SY5036-83) are spiral-seam steel pipes manufactured from hot-rolled steel coil blanks, formed into a spiral shape at room temperature, and welded using a double-sided submerged-arc welding method. They are used for the conveyance of pressurized fluids. These pipes offer high pressure-bearing capacity and excellent weldability. Having undergone various rigorous scientific inspections and tests, they are safe and reliable for use. With large diameters and high conveyance efficiency, they help reduce pipeline installation costs. They are primarily used in pipelines for transporting oil and natural gas.

6. Spiral-welded high-frequency welded steel pipes for conveying pressurized fluids (SY5038-83) are manufactured using hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using the high-frequency lap welding method. These spiral-welded high-frequency welded steel pipes are designed for the conveyance of pressurized fluids. These steel pipes offer high pressure-bearing capacity and good ductility, making them easy to weld and form. Having undergone various rigorous and scientific inspections and tests, they are safe and reliable in use. With large diameters, they provide high transportation efficiency and help reduce pipeline installation costs. They are primarily used for laying pipelines to transport petroleum, natural gas, and other fluids.

7. Spiral-welded submerged-arc welded steel pipes for general low-pressure fluid conveyance (SY5037-83) are manufactured using hot-rolled steel strip coils as pipe blanks, formed into a spiral shape at room temperature, and welded using double-sided automatic submerged-arc welding or single-sided welding methods. These pipes are designed for the conveyance of general low-pressure fluids such as water, gas, air, and steam.

8. Spiral-seam high-frequency welded steel pipes for general low-pressure fluid conveyance (SY5039-83) are manufactured using hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using the high-frequency lap welding method. They are intended for the conveyance of general low-pressure fluids.

9. Spiral-welded steel pipes for piles (SY5040-83) are manufactured using hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using double-sided submerged arc welding or high-frequency welding. These pipes are used for foundation piles in civil engineering structures, docks, bridges, and similar applications.

IV. Steel-Plastic Composite Pipes and Large-Diameter Coated Steel Pipes

Steel-plastic composite pipes use hot-dip galvanized steel pipes as the substrate, with plastic applied to the inner wall (and the outer wall if required) via powder fusion spraying technology, resulting in excellent performance. Compared to galvanized pipes, they offer advantages such as corrosion resistance, rust prevention, no scale buildup, smooth flow, cleanliness, non-toxicity, and a long service life. Tests indicate that the service life of steel-plastic composite pipes is more than three times that of galvanized pipes. Compared to plastic pipes, they offer higher mechanical strength, as well as superior pressure and heat resistance. Since the substrate is steel pipe, there are no issues with embrittlement or aging. They are widely applicable for the conveyance of fluids such as tap water, gas, and chemical products, as well as in heating systems, serving as an upgraded replacement for galvanized pipes. Since their installation and usage methods are essentially the same as those of traditional galvanized pipes, and the pipe fittings are identical, they can effectively replace aluminum-plastic composite pipes in large-diameter tap water conveyance. They are highly popular among users and have become one of the most competitive new products in the piping market.

Coated steel pipes are manufactured by applying a plastic coating to large-diameter spiral-welded or high-frequency-welded steel pipes, with a maximum outer diameter of 1,200 mm. Depending on specific requirements, they can be coated with various plastics—such as polyvinyl chloride (PVC), polyethylene (PE), epoxy resin (EPOZY), and other plastics with varying properties. They feature excellent adhesion and strong corrosion resistance, withstanding strong acids, strong alkalis, and other chemical corrosives. They are non-toxic, rust-free, wear-resistant, impact-resistant, and highly impermeable. The pipe surface is smooth and does not adhere to any substances, reducing flow resistance during transportation, improving flow rate and efficiency, and minimizing pressure loss. The coating contains no solvents or leachable substances, thus preventing contamination of the transported medium and ensuring the purity and hygiene of the fluid. It can withstand alternating hot and cold cycles within a temperature range of -40°C to +80°C without aging or cracking, making it suitable for use in harsh environments such as cold regions. Large-diameter coated steel pipes are widely used in engineering fields such as water supply, natural gas, petroleum, chemical, pharmaceutical, telecommunications, power, and marine applications.

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