As the core carriers for transporting fluids such as oil and natural gas, the material selection of line pipes directly affects the corrosion resistance, strength, and service life of the pipes. The following is a systematic classification and characteristic analysis based on the materials of line pipe:
I. Carbon Steel Line Pipes
Carbon steel pipes are the most widely used basic materials in pipeline engineering. They are mainly composed of iron-carbon alloys, and the carbon content is usually less than 1.7%. According to the difference in carbon content, they can be further divided into:
Low-carbon steel pipes (Q195 - Q235): With a carbon content of ≤ 0.25%, they have excellent welding performance and plasticity, and are used in low-pressure transportation systems, such as urban gas pipeline networks.
Medium-carbon steel pipes and high-carbon steel pipes (X42 - X70): Through micro-alloying treatment, elements such as niobium and vanadium are added to improve the strength. The tensile strength can reach over 485 MPa, and they are widely used in high - pressure long - distance transportation pipelines. A typical example is the X-series steel grades in the API 5L standard. Among them, the X70 steel grade has been successfully applied in the Third West - to - East Gas Pipeline Project.
II. Alloy Steel Line Pipes
To meet the requirements of extreme environments, alloy steel pipes are formed by adding elements such as chromium, molybdenum, and nickel:
Low - temperature - resistant steel pipes
Nickel-based steels (such as ASTM A333 Gr.3) with 2.5% - 9% nickel added can maintain toughness at a low temperature of - 196°C and are suitable for LNG transportation pipelines. The Yamal project in the Arctic Circle of Russia uses such materials.
Corrosion-resistant alloy pipes
Carbon steel pipes are lined with polyethylene (PE), polytetrafluoroethylene (PTFE), or ceramic layers, which not only retain the strength of the steel body but also improve the corrosion resistance. For example, the Shaanxi-Beijing Gas Pipeline uses PE-lined pipes, and the service life has been extended to 30 years.
