info@lefinsteel.com

+8615122229899

Home
About us
Products
Resource
Project
Service Capability
Certificates
Contact Us

中文

Home page

Details

HOT EXPANDED SEAMLESS PIPE
Definitions and basic concepts

Hot-expanded seamless steel pipe is a type of seamless steel pipe in which small-diameter seamless steel pipes are expanded to a larger diameter through a hot expansion process. Its core feature is to soften the steel pipe material by high-temperature heating, and then form it through mechanical expansion and shaping, ultimately creating large-diameter seamless pipes. This process overcomes the technical limitations of the traditional rolling process in the production of large-diameter seamless tubes and is widely used in industrial fields that require large diameters and high strength.

The specific steps of the hot expansion process

The hot expansion process mainly includes the following key steps:
Raw material preparation: Small-diameter seamless steel pipes are selected as raw materials, usually carbon steel, alloy steel or stainless steel.
- Heating: Use an induction heating furnace or gas furnace to heat the steel pipe as a whole or in part to 900°C to 1200°C (depending on the material), bringing the material to the temperature for plastic deformation.
- Expansion: Radial pressure is applied to the steel pipe through a hydraulic expansion machine or a cross-rolling expansion machine to gradually increase the inner diameter to the target size. During the expansion process, the shape of the mandrel (or die) controls the final dimensional accuracy of the steel pipe.
- Cooling and shaping: After expansion, slow cooling (such as air cooling or controlled cooling) is carried out, followed by straightening, end face cutting and other shaping treatments.
- Heat treatment: In some cases, normalizing or tempering is required to eliminate residual stress and optimize mechanical properties.
- Inspection and packaging: Defects are detected through ultrasonic, eddy current testing and other means. After passing the inspection, the products are packaged and delivered from the factory.
The uniqueness of the craftsmanship
- Enhanced material deformation capacity: At high temperatures, the plasticity of steel increases, allowing for a larger expansion rate (typically up to 20%-50%), enabling the production of steel pipes with a diameter of over 1.5 meters, far exceeding the traditional rolling limit.
- Low residual stress: The hot expansion process is accompanied by dynamic recrystallization, which reduces the residual stress caused by cold working and enhances fatigue resistance and corrosion resistance.
- Seamless structure maintenance: Compared with welded steel pipes, hot-expanded seamless pipes have no weld seams and better overall uniformity, making them suitable for high-pressure and high-temperature environments.
- Cost-effectiveness: Producing large tubes from small-diameter billets saves the equipment investment and energy consumption for direct rolling of large tubes.
Application field

Energy industry: Oil and gas transmission pipelines, especially submarine pipelines and high-pressure main lines.

Chemical equipment: high-temperature and high-pressure pipelines for reactors and heat exchangers.

Power industry: High-temperature and high-pressure resistant pipes for boilers.

Infrastructure construction: Large-diameter support pipes for Bridges and building structures.

Key points of quality control
- Temperature control: The uniformity of heating directly affects the uniformity of the wall thickness after expansion.
- Expansion rate: If it is too fast, it will cause local cracking. The expansion rate should be adjusted according to the material.
- Heat treatment process: Normalizing treatment refines grains and enhances toughness; Tempering reduces hardness and avoids brittleness.
- Non-destructive testing: 100% ultrasonic testing ensures no internal cracks or inclusions.
Compared with other processes

vs cold expansion (cold drawing) : Cold expansion has higher precision, but it is only limited to small expansion rates (<10%), and it has large residual stress and is prone to cracking.
vs welded pipe: Seamless structure has no weld weaknesses, higher pressure-bearing capacity, but the cost is higher.

Summary:

Hot-expanded seamless steel pipes achieve efficient production of large-sized seamless pipes through high-temperature plastic deformation, combining excellent material properties with cost advantages. They are key materials in fields such as energy and chemical engineering. The core of its process lies in the precise control of temperature and expansion, ensuring the reliability of the product in harsh environments.