Large-diameter welded steel pipe forming methods

The production of large-diameter welded steel pipes involves several advanced manufacturing methods, each suited to different specifications and applications. These pipes are crucial components in industries like construction, transportation, oil and gas, and infrastructure development, where strength, durability, and precision are essential. Below are the key production methods for large-diameter welded steel pipes.

Hot Push Expansion Method:
The hot push expansion method is a cost-effective and simple process that requires minimal maintenance. It is flexible in terms of product specifications, and additional accessories can be added to produce large-diameter welded steel pipes and other similar products. This method is suitable for the production of medium to thin-walled large-diameter welded steel pipes and can also produce thick-walled pipes, provided they do not exceed the equipment's capacity. The process is economical, durable, and widely used in manufacturing large-diameter pipes with varying specifications.

Hot Extrusion Method:
In the hot extrusion method, the billet is pre-processed by machining before extrusion. For small-diameter welded steel pipes (typically under 100mm), the investment in equipment is relatively low, and material waste is minimized. The technology is well-established and efficient for smaller pipes. However, as the diameter of the welded steel pipe increases, the process requires large-tonnage and high-power equipment, along with upgraded control systems, to maintain product quality and manufacturing efficiency.

Hot Piercing Rolling Method:
Hot piercing rolling primarily involves longitudinal extension and oblique extension. The main methods for longitudinal extension rolling include limited mandrel continuous rolling, less-frame limited mandrel continuous rolling, three-roller limited mandrel continuous rolling, and floating mandrel continuous rolling. These techniques are known for their high production efficiency, low metal consumption, and the ability to produce high-quality welded steel pipes with precise control. They are increasingly popular in the production of large-diameter welded steel pipes due to their excellent performance and scalability.

Main Production Processes for Large-Diameter Welded Steel Pipes in China

In China, the primary production processes for large-diameter welded steel pipes are hot-rolled large-diameter welded steel pipes and hot-expanded large-diameter welded steel pipes. Hot-expanded welded steel pipes, with diameters ranging from 325mm to 1220mm and wall thicknesses up to 120mm, are capable of producing non-standard sizes. These pipes are commonly referred to as hot-expanded steel pipes, which are produced through oblique rolling or drawing, resulting in a rough pipe finish.

This method is especially valuable for producing steel pipes with relatively low density but strong shrinkage properties. It is considered a key development trend in the field of rolled steel pipes, allowing manufacturers to thicken steel pipes in a short time, produce non-standard and specialized welded steel pipes, and achieve high production efficiency at lower costs.

Annealing Process

Before leaving the factory, large-diameter welded steel pipes undergo annealing and heat treatment. This delivery state is referred to as the annealed state. The primary purpose of annealing is to eliminate internal stresses and structural defects carried over from earlier stages of the manufacturing process, preparing the steel pipes for subsequent processes. This is especially important for alloy structural steel, structural steel for hardenability, cold heading steel, bearing steel, tool steel, turbine blade steel, and stainless heat-resistant steel. These materials are typically delivered in the annealed state to ensure optimal performance and durability.

Annealing plays a crucial role in ensuring the final quality of large-diameter welded steel pipes, improving their mechanical properties, and making them ready for their intended applications.