The medium-frequency hot expansion process is applied to large-diameter seamless steel pipe production. It was unprecedented in the industry at the time and not initially accepted by the domestic market. As the first to adopt this technology, the company faced significant resistance during the initial product launch and promotion. The company’s chairman took an innovative approach by first entering the international market. In 2004, they started exporting steel pipes, supplying to world-renowned companies such as France’s Alstom, America’s Fluor Corporation, and Japan’s JFE.

While not the mainstream method of steel pipe production, medium-frequency hot expansion plays a crucial role in filling gaps in manufacturing capabilities. It’s particularly useful for producing large-diameter, thin-walled, and ultra-thin-walled pipes that cannot be manufactured using traditional rolling processes. The hot expansion method uses an internal mandrel, resulting in pipes with consistent internal diameters, facilitating connection with pipe fittings. The wall thickness of large-diameter hot-expanded pipes is more uniform compared to rolled pipes of the same diameter. This process also offers advantages in small-batch production, multi-variety, multi-specification, and quick delivery.

The medium-frequency hot expansion process for seamless steel pipes involves heating qualified finished pipes continuously and uniformly from end to end using medium-frequency heating, while controlling temperature, speed, and expansion ratio. The mother pipe is expanded to a larger diameter by passing it over an internal conical mandrel, driven by the motion of a hydraulic cylinder piston.

Characteristics of Medium-Frequency Hot-Expanded Seamless Steel Pipes:

  1. Based on the principle of hot plastic deformation of steel, using finished pipes as mother pipes, with controlled temperature, speed, and expansion ratio during the expansion process.
  2. The metal in the deformation zone experiences compressive stress in both longitudinal and radial directions, and tensile stress in the circumferential direction, rather than unidirectional stress.
  3. One-step diameter expansion improves precision.
  4. Moderate and continuous uniform heating temperature reduces the likelihood of cracking.
  5. Continuous overall heating rather than localized heating.

Advantages of Medium-Frequency Hot-Expanded Seamless Steel Pipes:

  1. Flexible production, energy-efficient, and environmentally friendly, suitable for small-batch and multi-variety production.
  2. High material yield and low manufacturing costs.
  3. Good inner and outer surface quality with less iron oxide scale.
  4. High precision in wall thickness and inner/outer diameters, facilitating pipe fitting connections.
  5. Large diameters possible, up to 1500mm.
  6. Thin walls, with diameter-to-wall thickness ratios of 40-100 achievable.
  7. Long lengths, up to 12m for Φ762mm pipes.
  8. Strong adaptability to various steel grades.
  9. 100% finished product inspection ensures safety, reliability, and excellent quality.
  10. Nearly one million tons of hot-expanded products have been tested through long-term use by thousands of customers.