Production process ways of welded steel pipes

Steel pipes are classified into two main types based on their production methods: seamless steel pipes and welded steel pipes. This discussion will focus on welded steel pipes, also known as seamed steel pipes. These pipes are produced by bending and rolling steel plates or strips into desired cross-sections using various forming techniques. Welded steel pipes are known for their high precision in product dimensions, especially wall thickness, simpler production equipment, smaller operational footprint, continuous operation, and flexible production processes. They can be categorized into three types: spiral submerged arc welded pipes, straight seam double-sided submerged arc welded pipes, and straight seam high-frequency resistance welded pipes.

1. Spiral Submerged Arc Welded Pipe (SSAW)

Spiral steel pipes (SSAW) are manufactured using strip coil, welding wire, and flux as raw materials. The production process involves several steps: leveling the strip, trimming and planing the edges, cleaning the surface, conveying, and pre-bending. A welding gap control device ensures the welding gap meets the required standards, strictly managing the pipe diameter, misalignment, and weld gap. After cutting into individual pipes, the first three pipes of each batch undergo stringent inspections to verify mechanical properties, chemical composition, fusion state, and weld surface quality. Only after passing these quality and non-destructive inspections can the pipes proceed to full production.

2. Straight Seam Submerged Arc Welded Pipe (LSAW)

Straight seam submerged arc welded pipes (LSAW) are typically made from steel plates. The pipes are formed through various processes and welded using double-sided submerged arc welding, followed by post-weld expansion. The primary forming methods include UO (UOE), RB (RBE), and JCO (JCOE).

- UOE Straight Seam Submerged Arc Welded Pipe Forming Process:

The UOE forming process includes three main steps: pre-bending the steel plate, U forming, and O forming. Each step uses a specialized press to sequentially pre-bend the edges, U-form, and O-form the steel plate, ultimately shaping it into a circular tube.

- JCOE Straight Seam Submerged Arc Welded Pipe Forming Process:

In the JCOE process, the steel plate is stamped multiple times on a JCO forming machine. Initially, one half of the plate is pressed into a J shape, then the other half is also pressed into a J shape, forming a C shape. Finally, the middle is pressurized to form an open "O"-shaped tube blank.

3. Straight Seam High-Frequency Resistance Welded Pipe (ERW)

Straight seam high-frequency welded pipes (ERW) are produced by heating and melting the edges of the tube blank using the skin effect and proximity effect of high-frequency current after the hot-rolled coil is formed by a forming machine. The edges are then pressure-welded by an extrusion roller.

Understanding these production methods highlights the precision, efficiency, and versatility of welded steel pipes in various industrial applications.