Three production processes of welded steel pipes

Steel pipes can be classified into two main categories based on their production methods: seamless steel pipes and welded steel pipes. This overview will focus on welded steel pipes, also known as seamed steel pipes. The production process involves bending and rolling steel plates or strips into the required cross-sections using various forming techniques. Compared to seamless steel pipes, welded steel pipes offer higher product precision, especially in wall thickness, simpler main equipment, a smaller footprint, continuous operation, and flexible production capabilities. Welded pipes are further divided into three categories: 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)

The raw materials for spiral steel pipes (SSAW) include strip coil, welding wire, and flux. Before forming, the strip undergoes several processes: leveling, edge trimming, edge planing, surface cleaning, conveying, and pre-bending. A welding gap control device ensures that the welding gap meets the necessary requirements, strictly controlling pipe diameter, misalignment, and weld gap. After cutting the pipe into single units, the first three pipes of each batch undergo rigorous inspections to check mechanical properties, chemical composition, fusion state, and weld surface. Following these quality checks and non-destructive inspections, the pipe-making process can officially begin.

2. Straight Seam Submerged Arc Welded Pipe (LSAW)

Generally, straight seam submerged arc welded pipes (LSAW) are made from steel plates. Various forming processes are used to shape the welded pipe through double-sided submerged arc welding and post-weld expansion. The forming methods include UO (UOE), RB (RBE), and JCO (JCOE).

- UOE Straight Seam Submerged Arc Welded Pipe Forming Process:

The UOE LSAW steel pipe forming process involves three main steps: steel plate pre-bending, U forming, and O forming. Each step uses a specialized forming press to complete the edge pre-bending, U forming, and O forming sequentially, turning the steel plate into a circular tube.

- JCOE Straight Seam Submerged Arc Welded Pipe Forming Process:

In the JCOE process, the steel plate undergoes multiple stampings on a JCO forming machine. The first half of the steel plate is pressed into a J shape, then the other half is pressed into another J shape, forming a C shape. The middle is then pressurized to create an open "O"-shaped tube blank.

- Comparison of JCO and UO Forming Methods:

JCO Forming: This progressive pressure forming process transforms the traditional two-step UO forming into a multi-step process. The steel plate is uniformly deformed with minimal residual stress and no surface scratches. This method offers greater flexibility in wall thickness and size specifications, producing both large and small batches, including high-quality thick-walled pipes and small-diameter thick-walled pipes.

UO Forming: This method uses U and O pressure forming in two steps, characterized by high capacity and output. Annual production can range from 300,000 to 1,000,000 tons, making it suitable for mass production of single specifications.

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

Straight seam high-frequency welded pipes (ERW) are formed by using the skin effect and proximity effect of high-frequency current to heat and melt the edge of the tube blank after it is shaped by a forming machine from a hot-rolled coil. The edges are then pressure-welded under the action of an extrusion roller.

By understanding these detailed production methods, one can appreciate the precision, efficiency, and versatility of welded steel pipes in various industrial applications.