Large Diameter Steel Pipe

What is a large-diameter steel pipe?

Large-diameter steel pipes usually refer to steel pipes with a diameter of ≥159mm (6 inches). Some industry standards classify steel pipes with a diameter of ≥508mm (20 inches) as large-diameter steel pipes. This type of steel pipe is widely used in oil, natural gas, chemical industry, construction, shipbuilding and other fields due to its large diameter and thick wall.

Features of large-diameter steel pipes:

1. Strong pressure bearing capacity
Due to its large diameter and wall thickness (usually 12~120mm), large-diameter steel pipes can withstand high-pressure and high-flow media transportation, such as oil and natural gas.

Some X80 steel grade steel pipes can withstand low temperatures of minus 45℃ and are suitable for extreme environments.

2. Strong corrosion resistance
Using anti-corrosion coatings (such as epoxy resin, galvanized) or stainless steel materials (such as 304, 316), large-diameter steel pipes have good corrosion resistance and are suitable for various harsh environments, such as oceans and chemicals.

3. Excellent seismic performance
The optimized structural design can reduce the damage of earthquakes to the pipeline system.

4. Convenient installation
It can be prefabricated to reduce on-site welding and improve construction efficiency.

5. Smooth surface
The smooth surface of the steel pipe reduces the resistance during fluid transportation and improves the transportation efficiency.

6. High economic efficiency
Long service life, low maintenance cost, suitable for large projects.

7. Multiple uses
Widely used in oil, natural gas, water conservancy, chemical industry and other fields for transporting liquids and gases.

Types of large-diameter steel pipes:

1. Classification by manufacturing process
Seamless large-diameter steel pipe:
Features: No welds, high strength, high pressure resistance, often used in oil cracking, nuclear power, supercritical boilers, etc.

Welded large-diameter steel pipe (straight seam/spiral seam):
Features: low cost, simple production process, high production efficiency, often used in municipal drainage, medium and low pressure fluid transportation.

a. Spiral welded pipe (SSAW): Made by spiral welding process, the weld is spiral-shaped and has high strength. It is often used in long-distance oil and natural gas pipelines.

b. High-frequency welded pipe (ERW): Made by high-frequency current welding, the weld is in a straight line, the production process is simple, the production efficiency is high, and it is suitable for mass production.

c‌. Coated steel pipe ‌: Plastic is coated on the basis of large-diameter spiral welded pipe and high-frequency welded pipe to enhance corrosion resistance and service life.

2. Classification by material
Carbon steel (Q235, Q345): building structure, ordinary pipeline.
Alloy steel (15CrMo, P92): resistant to high temperature and high pressure, used in power station boilers and petrochemical equipment.
Stainless steel (304, 316): corrosion resistant, chemical and food industries.

Production method of large-diameter steel pipes:

The production process of large-diameter steel pipes is mainly divided into three categories: hot rolling, welding, and cold forming. The specific methods and characteristics are as follows:

1) Hot rolling process (applicable to seamless large-diameter steel pipes)

1. Hot extrusion method
Process: round steel billet → heating to 1200℃ → perforation → extrusion molding → sizing → cooling

Features:
Can produce Φ159~1200mm seamless pipes with a wall thickness of 20~120mm.
Dense organization and high pressure bearing capacity (such as P92 steel pipes for nuclear power).

Application: petroleum cracking pipes, supercritical boiler pipes.

2. Hot expansion method
Process: small-diameter seamless pipes → heating and expansion → cooling

Features:
Low cost, but poor wall thickness uniformity.
Suitable for Φ500~1500mm medium and low pressure pipelines (such as municipal drainage).

Disadvantages: large equipment investment and high cost.

2) Welding process (applicable to welded pipes)

1. Straight seam submerged arc welding (LSAW)
Process: steel plate → milling → pre-bending → JCO/UOE forming → internal and external welding → expansion

Features:
Mainstream process, can produce Φ406~1820mm steel pipes (such as X80 steel grade natural gas pipelines).
High weld quality and strong pressure bearing capacity.

Application: API 5L pipeline steel pipe.
Disadvantages: Low production efficiency.

2. Spiral submerged arc welding (SSAW)
Process: steel strip → spiral curling → welding → sizing

Features:
Can produce Φ219~3500mm ultra-large diameter steel pipes with high production efficiency.
Weld stress distribution is uniform, but the disadvantage is that ovality control is difficult.

Application: water supply, pile foundation pipe.

3. High-frequency resistance welding (ERW)
Process: steel coil → forming → high-frequency welding → heat treatment

Features:
Applicable to Φ114~660mm, wall thickness 3~40mm.
Low cost, but the weld needs strict quality inspection (non-destructive testing).

3) Cold forming process

1. Cold drawing/cold rolling
Process: hot-rolled tube billet → pickling → cold drawing/cold rolling → annealing

Features:
Can produce high-precision tubes (tolerance ±0.2mm).
Surface smooth (Ra≤1.6μm), used for hydraulic cylinder barrels.

2. Cold bending forming
Process: steel plate → continuous cold bending → welding (optional)

Features:
Suitable for special-shaped large-diameter tubes (square tubes, rectangular tubes).

Applications of large-diameter steel pipes:

1. Oil and natural gas fields
Transmission pipelines.
Oil cracking, drilling casing (API 5CT standard).

2. Chemical & Power Field
High-temperature and high-pressure pipelines (such as P92 and G115 steel for ultra-supercritical power plants).
Fertilizer equipment, heat exchangers.

3. Municipal Engineering
Urban water supply and drainage, sewage treatment.

4. Building & Bridge Field
Large-scale building support, cross-sea bridge structure.

5. Ship & Marine Engineering
Hull frame, offshore platform pipeline (seawater corrosion resistance).

Development and Trends:

Large-diameter steel pipes are developing towards high strength, intelligence, and greening. The core trends include:

a. Process innovation (continuous rolling, oblique rolling instead of hot expansion)
b. Material upgrade (alloying, compounding)

c. Application expansion (new scenarios such as hydrogen pipelines, deep sea and polar development)

Read more: Thick Wall Steel Pipe or Thin Wall Carbon Steel Pipe