Understanding the Production Characteristics of Longitudinally Welded Pipes

For longitudinal high-frequency welded steel pipes, high-frequency butt welding is employed, including high-frequency contact welding and high-frequency induction welding, with current frequencies ranging from 350-450 kHz. This welding method features simple production processes, high production efficiency, low cost, and rapid development. Let's delve into its production characteristics:

1. Fast Heating Speed, High Production Efficiency:

  - The energy is highly concentrated in the welding zone, heating the pipe edges to the required temperature within milliseconds to seconds, enabling high-speed welding without "skipping welds."

2. Wide Material Adaptability:

  - High-frequency resistance welding is a pressure welding method that does not require external filler metal, making it suitable for welding various metals such as carbon steel, alloy steel, and stainless steel.

3. Small Heat-Affected Zone:

  - The rapid welding speed and strong self-cooling effect of the workpiece result in a small heat-affected zone, reducing oxidation and improving the microstructure of the weld.

4. Uniform Wall Thickness, High Dimensional Accuracy:

  - Longitudinal high-frequency welded steel pipes, made from cold-formed rolled steel strips, exhibit uniform wall thickness and superior surface quality compared to seamless pipes. In particular, the dimensional accuracy of steel pipe is much better than seamless pipes and submerged arc welded pipes. At the same time, due to the use of hot-rolled steel strip as raw material, the internal defects of pipe body (such as cracks, inclusions, pores, etc.) are few, making them increasingly used as substitutes for seamless pipes in various applications. Due to the limitation of molding equipment and heating power, the size and wall thickness of the pipe diameter are limited, and the current pipe diameter is below Φ600mm and the wall thickness is below 13mm.

Recent advancements in hot-rolled steel strip quality, welding, heat treatment parameters, and online detection automation have greatly enhanced the reliability of longitudinal high-frequency welded steel pipes. They are now widely used in the petroleum and natural gas industries, particularly for long-distance pipelines and oil well casings.