What You Need to Know About Carbon Steel Pipes in Construction and Manufacturing

Carbon Steel Pipe  is one of the most widely used pipe materials in the industrial sector. It is mainly composed of iron (Fe) and carbon (C), with the carbon content typically ranging from 0.05% to 2.0%. It is supplemented by a small amount of silicon, manganese, sulfur, and phosphorus, etc.

Due to its high strength, high cost-effectiveness, and excellent processing performance, carbon steel pipes are widely used in multiple core industries such as oil and gas, construction, machinery, water conservancy, and power, and have become an indispensable basic material in industrial production and infrastructure construction.

Depending on the differences in manufacturing processes, carbon steel pipe content, and application scenarios, carbon steel pipes can be divided into various types. Among them, ERW Carbon Steel Pipe (resistive welding carbon steel pipe) is the core category of welded carbon steel pipes, and with its efficient and economical characteristics, it occupies a significant share of the global carbon steel pipe market. 

The Classification basis and categories

The main classification methods are as follows: one is based on carbon content, and the other is based on manufacturing process. These two methods are interrelated and jointly determine the performance and application scenarios of the pipes.

By carbon content classification: it can be divided into low-carbon steel (C ≤ 0.25%), medium-carbon steel (0.25% < C ≤ 0.6%), and high-carbon steel (C > 0.6%). Among them, low-carbon steel has good plasticity and is easy to weld, which is the main raw material for ERW Carbon Steel Pipe and is widely used in structural components and medium-low pressure fluid transportation; medium-carbon steel has higher strength and is mostly used in the manufacturing of mechanical parts; high-carbon steel has high hardness and good wear resistance, and is mainly used in tools, springs and other special scenarios.

According to manufacturing process: it can be divided into welded carbon steel pipes and seamless carbon steel pipes. Welded carbon steel pipes mainly adopt three processes: ERW (Electro-Roll Forming), LSAW (Longitudinal Submerged Arc Welding), and SSAW (Spiral Submerged Arc Welding). Among them, the ERW process is the most widely used type in welded carbon steel pipes due to its high production efficiency and controllable cost; seamless carbon steel pipes are produced through hot rolling or cold drawing processes, without weld seams, and have better pressure-bearing performance, suitable for high-temperature and high-pressure scenarios, but the production cost is significantly higher than that of ERW carbon steel pipes.

 The differences between ERW Carbon Steel Pipe & Seamless Carbon Steel Pipe

To better understand the industry positioning of ERW carbon steel pipes, the following compares the core differences between them and seamless carbon steel pipes, as well as LSAW/SSAW submerged arc welded carbon steel pipes:

Core Features and Industry Advantages

The reason why carbon steel pipes have become the mainstream pipe material in industry lies in their comprehensive characteristics that are suitable for various scenarios:

- Excellent mechanical properties: Moderate strength and toughness. The properties can be adjusted through heat treatment (such as annealing and normalizing) according to requirements, meeting the load-bearing requirements of different scenarios. Especially for low-carbon steel, the welding performance is excellent, providing a foundation for applications of welding processes such as ERW.

- Outstanding cost-performance ratio: Abundant reserves of raw materials (with the world's leading reserves of iron elements), mature production process, and manufacturing costs are much lower than those of stainless steel pipes and alloy steel pipes. In medium and low pressure, non-highly corrosive scenarios, it is the most cost-effective choice for pipe materials. This is also one of the core reasons why ERW carbon steel pipes have been widely popularized.

- Flexible processing capabilities: It can perform various processing methods such as cutting, welding, bending, and stamping, meeting the personalized needs of different projects. Among them, the cold bending forming process of ERW carbon steel pipes can produce pipes of various structural shapes, further expanding the application scope of carbon steel pipes.

- Limitations: Susceptible to corrosion. In corrosive environments such as dampness, acid and alkali, anti-corrosion treatment (such as hot galvanizing, epoxy coating) is required; Poor low-temperature toughness. In environments below -20℃, special low-temperature carbon steel pipes need to be selected to avoid brittle fracture. This characteristic should be particularly noted in outdoor and buried applications of ERW carbon steel pipes.

International standards of carbon steel

The production and testing of carbon steel pipes must comply with the globally unified industry standards to ensure product quality consistency. The core standards include:

- American Standard (ASTM/API):  ASTM A53 (ordinary purpose welded and seamless carbon steel pipes), ASTM A106 (high-temperature use seamless carbon steel pipes), API 5L (carbon steel pipes for oil and gas transportation, ERW carbon steel pipes used in oil and gas scenarios must comply with this standard), API Spec 5CT (carbon steel pipes for oil wells).

- National Standard (GB):  GB/T 3091-2015 (Welded Carbon Steel Pipes for Low-Pressure Fluid Transportation, clearly stipulating the production requirements for ERW carbon steel pipes), GB/T 8163 (Seamless Carbon Steel Pipes for Fluid Transportation), GB 5310 (Seamless Carbon Steel Pipes for High-Pressure Boilers), GB 6479 (Carbon Steel Pipes for Low-Temperature Pipelines).

- Specification (JIS):  JIS G 3452 (Carbon steel pipe for general purposes), JIS G 3454 (Carbon steel pipe for high-pressure applications). Among them, grades such as STKM11A and STPG370 are commonly used in the production of ERW carbon steel pipes.

The applications

ERW Carbon Steel Pipe, with its efficient, economical and stable quality characteristics, perfectly aligns with the overall application scope of carbon steel pipes. It also focuses on medium and low pressure, large-scale demand scenarios. The core application fields include:

In the field of oil and gas transportation: It is the core pipe material for oil and gas branch lines, urban natural gas pipelines, and oilfield gathering and transportation pipelines. The steel grades are mostly X56 - X80. After anti-corrosion treatment, it can be used for underground, cold regions, and even submarine transportation pipelines (in compliance with API 5L standards), but it is not suitable for main oil and gas pipelines; at the same time, it can be used to manufacture oil well pipes, suitable for oilfield extraction scenarios.

- Construction Engineering Field: Used for supporting building structures (such as scaffolding, support columns), water and drainage pipes, heating pipes. Commonly, ERW carbon steel pipes of grades Q235B, 20# etc. are used. With the advantages of low cost and easy processing, it helps reduce the cost of construction projects.

- In the field of mechanical manufacturing: It is used for manufacturing mechanical components, equipment supports, and car frames. It can be formed by cold bending into various shapes such as square and rectangular, meeting the structural requirements of different equipment.

-In the field of water conservancy and power: It is used for irrigation of farmland, urban drainage pipelines, and circulating water pipelines of power plants. In medium and low pressure scenarios, it can completely replace seamless carbon steel pipes, thereby reducing engineering investment.

- Other fields: It is used in fire protection pipelines, mine transportation pipelines (for non-corrosive and non-high-pressure scenarios), as well as in civilian applications such as furniture and guardrails. It is the most widely used type of welded carbon steel pipe.