Large diameter seamless steel pipe

What is Large Diameter Seamless Steel Pipe

Seamless steel pipe is a hollow, seamless pipe. Its manufacturing process eliminates welding or seam treatment, resulting in greater structural continuity and uniformity. Seamless steel pipe with an outer diameter greater than 108mm is generally referred to as large-diameter seamless steel pipe. It is commonly used in industrial applications requiring high pressure, high temperature, or to transport large volumes of fluid. Due to its unique manufacturing process and structural characteristics, this type of steel pipe plays an irreplaceable role in a variety of fields.

Production Process for Large Diameter Seamless Steel Pipe

1. Hot Rolling

This is the primary method for producing large-diameter seamless steel pipe.

The round billet is first heated to 1100-1250°C to achieve good plasticity. The solid billet is then punched through a piercing mill to form a hollow shell.

The shell undergoes multiple rolling passes (such as three-roll cross-rolling, continuous rolling, or extrusion) to gradually reduce its outer diameter and wall thickness to the desired size. The shell then undergoes subsequent processing steps such as sizing, cooling, straightening, and flaw detection.

2. Cold Drawing/Cold Rolling Process

For large-diameter seamless steel pipes requiring higher precision and thinner wall thickness, cold drawing or cold rolling is performed in addition to hot rolling.

Cold drawing involves drawing the hot-rolled steel pipe through a specific die to achieve more precise dimensions. Cold rolling, on the other hand, involves rolling the steel pipe using a rolling mill. This can further improve surface quality and dimensional accuracy, but it also results in relatively low production efficiency.

3. Key Production Technologies

Key manufacturing technologies include temperature control, deformation rate adjustment, and cooling treatment, which directly impact the mechanical properties and microstructure of the steel pipe.

For example, an appropriate cooling rate can refine the grain size, improving the material's strength and corrosion resistance. Large-diameter seamless steel pipes also undergo non-destructive testing, such as ultrasonic or radiographic testing, to ensure the absence of internal defects.

4. Production Process

Round tube billet → heating → piercing → three-roll cross rolling, continuous rolling, or extrusion → stripping → sizing (or reducing diameter) → cooling → straightening → hydraulic testing (or flaw detection) → marking → warehousing

Material Selection for Large Diameter Seamless Steel Pipes

Seamless steel pipes are typically made of carbon steel, alloy steel, or stainless steel, with the specific choice depending on the application.

1. Carbon Steel

Such as Q235 and 20# steel. Q235 is relatively inexpensive and offers reasonable strength and toughness, making it commonly used for general structural components and fluid pipelines.

20# steel offers excellent overall performance and is widely used. It can be used to manufacture mechanical parts and fluid pipelines where strength requirements are not high.

2. Low-Alloy Steel

Such as Q345 and Q390.

By adding alloying elements, these steels offer superior strength, toughness, and corrosion resistance compared to carbon steel. They are suitable for manufacturing structural components subject to heavy loads and harsh environments, such as support structures for bridges and large buildings.

3. Alloy Steel

For example, 40Cr and 20CrMo.

This type of steel offers higher strength, hardness, and excellent hardenability, and is often used in the manufacture of important mechanical parts, such as drive shafts for large equipment and high-pressure pipelines.

4. Stainless Steel

Common examples include 304 and 316L.

Large-diameter seamless stainless steel pipes offer excellent corrosion resistance and are suitable for use in industries requiring high corrosion resistance, such as the food, chemical, and medical industries, for conveying corrosive media or operating in corrosive environments.

Specifications of Large-Diameter Seamless Steel Pipes

1. Calculating the Weight of Large-Diameter Seamless Steel Pipes

[(Outer Diameter - Wall Thickness) * Wall Thickness] * 0.02466 = kg/m (weight per meter)

2. General Specifications

General Specifications of Large-Diameter Seamless Steel Pipes:

The diameter of large-diameter seamless steel pipes typically ranges from 108mm to 1200mm, with larger sizes available, even up to 3600mm. Wall thickness varies depending on specific needs and can range from 5mm to 50mm.

Large-diameter seamless steel pipes adhere to international standards such as API. Common specifications include DN150, DN200, and DN250.

Advantages of Large-Diameter Seamless Steel Pipes

1. Structural Uniformity

The seamless design avoids stress concentration and improves pressure-bearing capacity.

2. Mechanical Strength

Through heat treatment and process optimization, a balance of high strength and toughness can be achieved.

3. Corrosion Resistance

Material selection and surface treatments (such as plating or coating) can extend service life.

Applications of Large-Diameter Seamless Steel Pipes

Large-diameter seamless steel pipes are widely used in industries such as energy, chemical, transportation, and construction.

1. Energy

Large-diameter seamless steel pipes are used in long-distance oil and natural gas pipelines and superheater tubes in power plant boilers.

These applications require the pipes to withstand high pressures and temperatures while reducing the risk of leaks.

2. Chemical Industry

Seamless steel pipes are used in reactors, heat exchangers, and pipelines transporting corrosive chemicals. Their seamless structure reduces the possibility of media carryover and contamination.

3. Transportation

Large-diameter steel pipes are used in bridge support structures and shipbuilding, providing the necessary strength and durability.

4. Construction

These pipes serve as pillars or frames for large structures, playing a particularly important role in long-span buildings such as stadiums and airports.

Read more: Cutting method of large diameter seamless steel pipe