Full-process integrated steel manufacturing

I. Seamless Steel Pipes

Core Feature:There is no joint around the entire pipe circumference. Seamless pipes are manufactured by piercing solid steel billets.

Manufacturing of Seamless Pipes (Mannesmann Pipe Rolling Process)

Manufacturing of Seamless Pipes (Hot Extrusion — Hot Hollow Forging)

Main Manufacturing Processes

1. Hot Rolling (Hot Extrusion) Process (Main Production Method)

Process flow: Round solid pipe billet → Heated to a plastic state in a heating furnace → Pierced by a piercing mill to form hollow shell → Rolled by a pipe rolling mill for elongation, wall thinning and sizing → Finishing via sizing mill/reducing mill → Cooling → Straightening → Cutting → Inspection

Representative processes: Mannesmann piercing process, cross rolling piercing, etc.

Features: High production efficiency; capable of producing large-diameter and thick-walled pipes. It is the mainstream production process.

2. Cold Drawing (Cold Rolling) Process

Process flow: Hot-rolled pipe as raw material → Pickling to remove oxide scale → Phosphating and saponification for lubrication → Drawing via cold drawing machine with dies or rolling by cold rolling mill → Heat treatment to eliminate internal stress → Straightening → Finishing

Features: High dimensional accuracy, excellent surface finish and superior mechanical properties. It has high production costs and low output, and is mostly used for small-diameter, precision or thin-walled pipes.

Advantages

• Uniform mechanical properties: Without weld seams, the pipe has consistent metallographic structure in circumferential and longitudinal directions, with strong pressure resistance.

• High pressure resistance and corrosion resistance: Applicable to high-pressure, extreme temperature and corrosive working environments, such as boiler tubes and hydraulic cylinder barrels.

• Diversified cross-sectional shapes: Can be made into round, square, oval and other complex cross-sections.

Disadvantages

• High production cost: The process is complicated, with high energy consumption and large metal loss, leading to a low finished product rate.

• Difficult to control wall thickness uniformity: Eccentricity and surface defects may appear on the inner wall, especially for thick-walled pipes.

• Limited specifications: Restricted by raw billets and production equipment, the single pipe length and maximum outer diameter (generally ≤ Φ660mm) are limited.

II. Longitudinally Welded Pipes

Core Feature:It has a single straight weld parallel to the pipe axis, which is made by rolling steel plates or steel strips and then conducting welding.

Resistance Welded Pipe

Main Manufacturing Processes

1. High-Frequency Longitudinal Welded Pipes

• JCOE Forming: Pre-bend the edges of steel plates first, then gradually press the plates into a cylinder through J-type, C-type and O-type dies, and conduct diameter expanding finally.

• UOE Forming: Pre-bend plate edges first, press the plates into U-shape and then O-shape, and expand the diameter after welding. This process requires large equipment investment and is suitable for mass production.

Typical Applications

• High-frequency welded pipes: Building structures (scaffolding), furniture, low-pressure fluid transportation, automobile drive shaft tubes.

• Submerged-arc welded pipes: Long-distance oil and gas transmission pipelines, offshore platform structural pipes, urban pipe networks, wind turbine tower cylinders.

Advantages

1. High production efficiency and low cost: Especially for high-frequency welded pipes, continuous high-speed production can be realized.

2. High dimensional accuracy and good surface quality: Made from pre-processed steel plates, the pipes have uniform wall thickness and fine appearance.

3. Strong flexibility: Pipes of different diameters can be produced by changing the width of raw steel strips.

Disadvantages

1. Existence of a longitudinal weld seam: The weld is a potential weak part, so extremely high requirements are set for welding quality.

2. Diameter limited by plate width: The pipe diameter is generally restricted by the width of the steel plate.

III. Spiral Welded Pipes

Core Feature:The weld seam spirals around the pipe body. It is also manufactured by rolling and welding steel plates or steel strips.

Main Manufacturing Processes: Forming and Welding

Advantages

1. Extremely high flexibility: Multiple pipe diameters can be produced with steel strips of a single width.

2. Weld avoids the main stress direction: The spiral weld forms an angle with the main stress direction, making the load-bearing capacity of the pipe body more balanced in this direction.

3. Weld defects are hard to spread through the pipe: The spiral structure lengthens the propagation path of cracks.

4. Relatively low equipment investment: Suitable for producing medium and large-diameter pipes.

Disadvantages

1. Long weld seam: The weld length is 30%~100% longer than that of longitudinally welded pipes, which increases welding workload and unstable factors.

2. Inferior dimensional accuracy: The roundness and straightness are generally worse than those of longitudinally welded pipes.

3. Severe internal stress: The internal stress generated during forming and welding is more complex.

4. Relatively low production speed.

Typical Applications