Large diameter seamless steel pipe thermal forming manufacturing process

The thermal forming manufacturing process for large-diameter seamless steel pipes involves two main methods: hot rolling and hot extrusion. Hot rolling is primarily used to produce composite pipe joints, while hot extrusion is suitable for the production of seamless composite pipes. This article briefly introduces these thermal forming manufacturing processes for large-diameter seamless steel pipes.

Hot Rolling

Hot rolling is a traditional method for producing large-diameter seamless steel pipes. The process essentially involves pressure welding, where the metal's surface oxide film is broken by the pressure exerted by the rolling process. This allows the atomic surfaces to come into contact and weld together.

- Advantages of Hot Rolling:

High Productivity: Hot rolling can produce large quantities of pipes efficiently.

Good Quality: The method ensures high-quality pipes with consistent properties.

Low Cost: It is a cost-effective method that minimizes material loss.

Wide Application: Suitable for producing composite materials, particularly for pipes with a wall thickness of less than 32mm.

- Disadvantages of Hot Rolling:

High Initial Investment: The setup cost for hot rolling is significant.

Material Limitations: Not all material combinations can be achieved through rolling, especially complex ones.

Currently, hot rolling is widely used for manufacturing carbon steel and stainless steel composite pipe joints.

Hot Extrusion

Hot extrusion is typically used for producing double metal tubes, a process known as composite extrusion (coextrusion). This method is particularly effective for manufacturing seamless composite pipes from stainless steel and high nickel alloys.

- Advantages of Hot Extrusion:

Metallurgical Bonding: The interface between metals is metallurgically bonded, ensuring strong adhesion.

Suitable for High-Alloy Processing: This method is well-suited for metals with high alloy content and low plasticity, which are difficult to process using other methods.

- Disadvantages of Hot Extrusion:

Interface Diffusion: The bonding depends on rapid interface diffusion during the extrusion process, which can be affected by the presence of oxide films.

Material Limitations: Currently, composite extrusion is mainly used for combining carbon steel, stainless steel, and high nickel alloys.

There are three primary ways to prepare composite tubes before extrusion:

Forging Billet Piercing and Amplification: The billet is forged and pierced to create a hollow shape, then extruded.

Direct Centrifugal Spin Casting: This method involves casting the metal directly into a spinning mold to form the tube.

Using Corrosion-Resistant Powder Particles: The inner and outer layers of the tube are made from corrosion-resistant powders, known as "NUVAL" technology, although this method is costly due to powder preparation.

To achieve higher surface quality, the hot-extruded tubes often undergo additional rolling or drawing processes after extrusion.

Conclusion

Both hot rolling and hot extrusion are effective thermal forming methods for manufacturing large-diameter seamless steel pipes. Hot rolling offers high productivity, good quality, and cost efficiency, making it suitable for various composite materials. On the other hand, hot extrusion provides strong metallurgical bonding and is ideal for processing high-alloy metals. Understanding the advantages and limitations of each method helps in selecting the appropriate process for specific applications in the production of seamless steel pipes.