Large diameter seamless steel pipe

Large diameter seamless steel pipes generally refer to large-sized steel pipes with an outer diameter of 300 millimeters or more, which are formed in one piece through processes such as hot rolling or hot expansion, and have no welds in the pipe body. This type of steel pipe features uniform pressure resistance, strong fatigue resistance and a smooth inner wall. It is widely used in water transmission, gas transmission, chemical industry, Marine engineering and high-pressure boilers, etc.

Raw materials and chemical composition

1. Carbon steel: This is an alloy of steel and carbon, and it is a widely used material with typical grades such as ASTM A36, EN 10025-2, etc. It has good weldability and low cost, and is suitable for structural engineering and general water supply and drainage.

2. Stainless steel: Stainless steel is a metal with extremely strong corrosion resistance and is widely used in highly corrosive environments, such as chemical, Marine, and food-grade pipelines. Common grades include 304, 316L, 321H, etc.

3. Alloy steel: It features high-temperature resistance and creep resistance, and is widely used in high-pressure boiler equipment and chemical plants. Common grades include P11, P22, etc.

4. Pipeline steel: Pipeline steel features high strength and excellent low-temperature toughness, and is widely used in oil and gas pipelines. Common grades include API 5L X42, X52, X60, X70, and X80.

The main manufacturing process

Preparation of raw materials: Prepare round cast, rolled or forged billets, preheated to  1150  ° C   ~  1250  ° C.
Piercing: The initial hole is formed by rotating the plug bar. For large-diameter billets, the hole is first milled and then expanded by hot rolling.
Hot rolling/hot expansion: The inner diameter is gradually expanded at high temperatures through an expansion machine.
Sizing and straightening: The pipe material passes through the sizing machine and straightening machine to correct the outer diameter, roundness and straightness, and the compressive stress is eliminated.
Heat treatment: Normalizing, annealing or quenching + tempering: Select based on the material and application to optimize mechanical properties and microstructure.
Cutting and end face processing: Cut to the required length as per customer requirements, turn, chamfer or wire.
Surface treatment: pickling, phosphating, sandblasting or painting/plastic coating to enhance anti-corrosion ability.

Mechanical properties and main advantages

High strength and high toughness, tensile strength can reach 490         650 MPa, impact toughness meet   -     20 ℃   ~   -     40 ℃   requirements at low temperature.
High and low temperature resistance: Large-diameter seamless steel pipes made of alloy steel and stainless steel can be used for a long time within the range of   -  196 ℃  -  600 ℃.
No welds: The steel pipe as a whole has no weld defects, uniform pressure resistance, and excellent fatigue resistance.
High fluid transmission efficiency: The inner wall is smooth, ensuring high fluid transmission efficiency during transportation. Moreover, the friction between the steel pipe and the fluid is reduced, thereby minimizing the wear and tear of the steel pipe.

Application field

Water and gas transmission pipelines: urban water supply, natural gas and irrigation systems.
Petroleum and Chemical industry: Transporting oil products and chemicals in high-temperature and high-pressure environments.
High-pressure boilers and pressure vessels: Applicable to pressure-bearing components of boilers and storage tanks.

Municipal and infrastructure: Bridge pile foundation, building support, Marine platform structure support.
Defense applications: such as missile tubes, submarine system pipelines.

Summary

Large-diameter seamless steel pipes, with their high strength, corrosion resistance, strong pressure-bearing capacity, seamless structure and high transmission efficiency, are irreplaceable in conveying systems, infrastructure, high-pressure equipment, chemical industry, petroleum and national defense equipment. The three processes of hot rolling, hot expansion and cold rolling ensure its size and performance. Combined with multi-standard testing and material customization, it meets the complex engineering requirements.