Carbon steel pipe: the "tubular foundation" of industrial fluid transportation and structural support

In industrial production and infrastructure construction, carbon steel pipe, with its unique hollow tubular structure, has become a core material for connecting fluid transport (oil, gas, water, and chemical media) with structural support (buildings and machinery). Made from carbon steel, it is seamlessly rolled or welded into a tubular form. Compared to flat carbon steel plates or coils, carbon steel pipe is more suitable for long-distance transportation and three-dimensional support. It is widely used in fields such as petrochemicals, municipal engineering, machinery manufacturing, and architectural steel structures, becoming an indispensable "blood vessel" in the industrial system.

I. Basic Concepts and Structural Characteristics of Carbon Steel Pipe

The core composition of carbon steel pipe is the same as that of carbon steel plates and coils, based on iron (Fe) and carbon (C) (carbon content ≤ 2.11%), with trace elements such as manganese, silicon, sulfur, and phosphorus. Carbon content remains a key indicator for controlling strength and hardness. Its essential difference lies in its hollow tubular structure and manufacturing logic: By processing carbon steel billets into tubes with open ends and round, square, or shaped cross-sections, these tubes function as fluid channels or load-bearing structures. Diameters (inner and outer diameters) range from 6mm (thin tubes) to 3000mm (large-diameter welded pipes), and lengths can be customized (typically 6-12m, with large-diameter welded pipes capable of up to 18m).

The tubular structure offers two core benefits: efficient fluid transport. The hollow channel allows for low-resistance transport of liquids, gases, powders, and other media, increasing efficiency by 40%-60% compared to traditional trough-type conveying. Second, lightweight support. Tubular structures offer superior bending and torsional strength to solid steel at the same weight (for example, a carbon steel tube of equal weight has 30% greater bending strength than round steel), making them suitable for lightweight design in the construction and machinery sectors.
II. Core Classification of Carbon Steel Pipes (Based on Manufacturing Process)
The manufacturing process is a key factor in determining the performance, cost, and application of carbon steel pipes. The mainstream categories are seamless and welded, accounting for over 95% of total carbon steel pipe production.
(I) Seamless Carbon Steel Pipe: No Welds, the Preferred Choice for High-Pressure Applications
Seamless pipes are manufactured by directly rolling steel billets into tubular form. They have no welded seams and offer high overall strength and pressure resistance, making them suitable for conveying high-pressure, high-temperature, and corrosive media. Based on the rolling process, they can be further categorized as follows:
Hot-Rolled Seamless Pipes
Process: Round billets (50-300mm in diameter) heated to approximately 1200°C are punched through a piercing mill to form hollow tubes. These tubes are then rolled through a hot rolling mill to form the tubes, followed by sizing and straightening. Features: Wide wall thickness tolerance (±5%-8%), surface scale, diameter range 25-630mm, pressure rating 10-30MPa, excellent toughness, suitable for medium- and high-pressure fluid transportation.
Applications: Oil drilling and production tubing (oil well pipe), high-pressure boiler pipes (for power plant boilers), hydraulic support pipes (for coal mining machinery). For example, Φ139.7mm hot-rolled seamless pipe for oilfields can withstand high-pressure oil and gas from wells 3,000 meters underground.
Cold-drawn/Cold-rolled Seamless Pipe
Process: Hot-rolled seamless pipe is drawn into thin tubes at room temperature using a cold drawing mill (drawing force 50-200 tons), or subjected to high-precision rolling in a cold rolling mill. Annealing is then required to eliminate internal stresses. Features: Extremely tight wall thickness tolerance (±1%-3%), smooth surface (roughness Ra ≤ 1.6μm), diameter range 6-200mm, pressure rating exceeding 40MPa, and high dimensional accuracy.
Applications: Automotive hydraulic tubing (brake hoses, oil pipes), precision machinery bearing sleeves, and medical device tubing (such as syringe needle blanks). For example, Φ10×1.5mm cold-drawn seamless tubing is commonly used for automotive hydraulic tubing and can withstand 35MPa braking pressure.
(II) Welded Carbon Steel Pipe: Welded, Cost-Effective, and the Mainstay for Large Diameters
Welded pipe is made from carbon steel coils (or carbon steel plates cut into strips) by bending them into tubular form and then welding the seams. Its cost is only 60%-80% of that of seamless pipe of the same specification, making it suitable for low-pressure, large-diameter applications. By welding process:

Elongated Seam Welded Pipe (ERW)

Process: Carbon steel coils are slit into fixed-width strips, continuously bent into round/square shapes using a forming machine. The seams are then fused using high-frequency induction welding (1300-1500°C), and the pipes are sized and cut.

Features: The weld seam runs along the length of the pipe. Available diameters range from 15-630mm, lengths from 6-12m, and pressure ratings from 2-10MPa. Production efficiency is high (10-20 meters per minute).

Applications: Municipal water supply pipes, gas pipes (low-pressure), and steel structure columns. For example, residential gas pipes often use Ø110mm ERW pipes with a pressure rating of ≤4MPa, meeting residential gas safety standards.

Spiral Welded Pipe (SSAW)

Process: Carbon steel coils are bent into a helical shape and welded using submerged arc welding (where the wire melts and fills the seam). The resulting spiral weld seam allows for the production of large-diameter pipes. Features: The weld distributes stress, resulting in superior crack resistance compared to straight seam welded pipe. Available in diameters from 219 to 3000mm, with single lengths up to 18m, and a pressure rating of 3 to 15MPa, it is suitable for long-distance transportation.
Applications: Interregional oil and gas pipelines (such as the West-East Gas Pipeline), municipal sewage pipes, and large storage tank columns. For example, the Φ1219mm spirally welded pipe used in the West-East Gas Pipeline II can withstand a pressure of 10MPa and is available in single lengths of 12m, reducing the number of pipeline connections. (III) Other Classification Methods

By Diameter: Small Diameter Pipes (≤50mm, such as machinery pipes), Medium Diameter Pipes (50-200mm, such as water supply pipes), Large Diameter Pipes (≥200mm, such as gas pipes);

By Cross-Sectional Shape: Circular Pipes (mainstream, accounting for over 80%), Square Pipes (for building steel structures), Rectangular Pipes (for furniture and guardrails);

By Surface Treatment: Galvanized Welded Pipes (hot-dip galvanizing increases corrosion resistance by five times, used for outdoor guardrails); Anti-Corrosion Coated Pipes (3PE coating, used for oilfield pipelines, resistant to soil corrosion).

III. Key Performance Advantages of Carbon Steel Pipes

The performance advantages of carbon steel pipes are deeply integrated with their "tubular structure + manufacturing process," precisely matching the needs of different scenarios:

Balanced pressure and impact resistance

Seamless pipes, due to their lack of welds, offer uniform mechanical properties throughout and are less susceptible to cracking under high pressures of 10-40 MPa. For example, a Φ325mm hot-rolled seamless pipe used in power plant boilers can withstand temperatures of 300°C and steam pressures of 25 MPa. Welded pipes, with their spiral welds, distribute stress and offer excellent impact resistance in low-pressure environments. For example, when a municipal sewage pipe is impacted by ground subsidence, the spiral welds are less likely to fracture.

High Fluid Transport Efficiency

The smooth inner wall (cold-drawn seamless pipe inner wall roughness ≤ 0.8μm) reduces fluid resistance and achieves transport efficiency over 30% higher than concrete pipe. For example, a Φ1200mm spirally welded gas pipeline can transport up to 10 million cubic meters of gas per day, meeting the gas needs of a city with a population of one million. Strong Cost and Application Compatibility

Welded pipe is made from carbon steel coils, featuring a simple production process and a cost of only 60%-70% of seamless pipe, making it suitable for low-pressure, large-diameter applications. While seamless pipe may be more expensive, it offers superior high-pressure performance and can replace expensive alloy pipes. For example, cold-drawn seamless pipe for hydraulic systems offers a cost-effectiveness that is twice that of stainless steel.

Excellent Modifiability and Weather Resistance

Corrosion resistance can be enhanced through surface treatment: Galvanized welded pipe offers up to 5,000 hours of salt spray corrosion resistance (compared to 1,000 hours for conventional welded pipe), making it suitable for outdoor guardrails. 3PE anti-corrosion coated pipe (polyethylene + adhesive + epoxy powder) offers up to 30 years of soil corrosion resistance and is suitable for deep well pipelines in oilfields.

IV. Key Application Areas of Carbon Steel Pipes

The tubular nature of carbon steel pipes enables them to cover two core scenarios: transportation and support. Downstream applications are concentrated in the following industries:

(I) Petrochemical Industry (Approximately 30%)

Oil and Gas Transportation: Spiral welded pipes (3PE corrosion protection) with diameters of 219-1219mm are used for laying long-distance pipelines, such as the West-East Gas Pipeline and the China-Russia Crude Oil Pipeline, and can withstand pressures of 10-15MPa.

Oilfield Drilling and Production: Hot-rolled seamless pipes with diameters of 73-177.8mm are used for oil well pipes (casings and tubing), capable of withstanding high temperatures and pressures (300°C, 30MPa) and formation corrosion.

Chemical Equipment: Cold-drawn seamless pipes with diameters of 15-50mm are used for reactor feed pipes and cooling water pipes, resistant to corrosion from chemical media (such as hydrochloric acid and ethanol). (II) Municipal Engineering (approximately 25%)
Water Supply/Sewage: Use Φ110-630mm straight seam welded pipes (lined with cement mortar for corrosion protection). For example, urban water supply networks use Φ315mm straight seam welded pipes, with a daily water supply of up to 50,000 tons.
Gas Transmission: Use Φ50-315mm galvanized straight seam welded pipes (low pressure). Φ25-50mm galvanized pipes are commonly used for gas branch pipes in residential communities to ensure gas safety.
Urban Pipeline Renovation: Use Φ630-1600mm spiral welded pipes to replace old concrete pipes, improving the network's compressive strength (capable of withstanding a 10-ton ground vehicle load). (III) Machinery Manufacturing (approximately 20%)
Hydraulic Systems: Φ6-50mm cold-drawn seamless pipes (H8 precision) are used for automobile brake pipes and excavator hydraulic hoses. They can withstand pressures of 30-40MPa, ensuring precise movement.
Bearings and Bushings: Φ10-100mm cold-rolled seamless pipes are used for motor bearing sleeves. The inner wall precision reaches IT7, reducing operating friction.
Agricultural Machinery Parts: Φ20-80mm hot-rolled seamless pipes are used for tractor drive shaft sleeves. They have a torsional strength of 400MPa and are suitable for rough field conditions. (IV) Construction and Steel Structure (approximately 15%)
Steel structure support: 100-300mm Ø straight seam welded pipes are used for factory columns and bridge guardrails. For example, 219×8mm Ø straight seam welded pipes are used for steel structure factories, and each pipe can bear a load of 50 tons.
Scaffolding: 48×3.5mm Ø straight seam welded pipes (galvanized) are used. They are lightweight and corrosion-resistant, commonly used in construction, and can bear a load of up to 1.5 tons per pipe.
Decorative structures: 20-50mm Ø square/rectangular welded pipes are used for shopping mall guardrails and stair handrails. The surface can be painted or brushed, combining aesthetics with strength.​
V. Future Development Trends of Carbon Steel Pipes

With the increasing demand for industrial upgrading and infrastructure construction, carbon steel pipes are developing towards "high strength, large diameter, green, and intelligent" characteristics:

High strength to suit high-pressure applications

Development of "micro-alloyed seamless pipes" with the addition of niobium and vanadium. When the carbon content is ≤0.2%, the yield strength is increased to over 550 MPa (compared to approximately 345 MPa for ordinary seamless pipes). This can be used for deep-sea oil and gas transportation (3,000 meters underwater, 50 MPa pressure), replacing expensive alloy pipes.

Large diameters to meet infrastructure needs

Breakthroughs in the manufacturing technology of spiral welded pipes over 3,000 mm in diameter are being developed for use in ultra-large oil storage tanks and urban integrated pipeline corridors. For example, 3,600 mm in diameter spiral welded pipes can be used as urban stormwater mains, with a daily drainage capacity of up to 500,000 tons, reducing pipeline corridor construction costs. Green Manufacturing Reduces Carbon Emissions

Promoting the "Short-Process Steelmaking - Seamless Pipe" process: Using scrap steel as raw material (instead of iron ore), steel is smelted in an electric arc furnace and then rolled into seamless pipes. This reduces carbon emissions by 65% ​​compared to the traditional long process. The introduction of "continuous welding + waste heat recovery" technology in welded pipe production reduces energy consumption by 20%.

Intelligent Manufacturing Improves Quality Stability

The addition of AI-powered visual inspection (with an accuracy of 0.1mm) to the welding process allows for real-time identification of weld defects (such as cracks and lack of fusion), increasing the pass rate to 99.5%. Digital twin technology is being introduced in seamless pipe rolling to simulate wall thickness accuracy under different billet parameters, reducing trial rolling waste.

Conclusion
Although carbon steel pipes belong to the same carbon steel family as carbon steel plates and carbon steel coils, their hollow tubular structure has opened up unique applications. They serve as both the "blood vessels" for industrial fluids (oil, gas, water, and chemical media) and the "support framework" (columns and bushings) for construction machinery. From the thousands of miles of West-East Gas Pipelines to the capillaries of urban water supply networks, from the precision fittings of automotive hydraulic systems to the load-bearing columns of steel-structured factories, carbon steel pipes permeate both industry and daily life. In the future, with the integration of high-strength materials, green processes, and intelligent manufacturing, carbon steel pipes will continue to support global infrastructure upgrades and high-quality industrial development with their advantages of "efficiency, cost-effectiveness, and reliability."