How are welded steel pipes processed?

Steel pipes are generally classified into two main types based on their production methods: seamless steel pipes and welded steel pipes. Welded steel pipes, also known as seamed pipes, are produced by curling and forming steel plates or strips and then welding them along the seam. These pipes are typically manufactured in lengths of 6 meters. The production process of welded steel pipes is straightforward, with high production efficiency, a wide variety of specifications, and relatively low equipment investment. However, their overall strength is generally lower than that of seamless steel pipes. Below, we'll delve into the processing methods for welded steel pipes, as explained by a carbon steel pipe manufacturer.

Understanding the Processing of Welded Steel Pipes

Welded steel pipes, also known as seamed steel pipes, are created by bending a pipe blank (which can be a steel plate or strip) into a pipe with the desired cross-sectional shape and size. This is achieved through various forming methods, followed by welding the seams using different welding techniques. Compared to seamless steel pipes, welded steel pipes offer higher precision, especially in wall thickness accuracy. The main equipment used is simpler, requiring less space, and production can continue uninterrupted with flexible operation and a wide range of products.

Welded pipes can be categorized into three main types based on production technology:

Spiral Submerged Arc Welded (SSAW) Pipes

Longitudinal Submerged Arc Welded (LSAW) Pipes

Straight Seam High-Frequency Resistance Welded (ERW) Pipes

1. Production Process of Spiral Steel Pipes

Spiral steel pipes are primarily made from steel strip coils, welding wire, and flux. The process involves several steps:

Preparation: The steel strip is leveled, trimmed, cleaned, and pre-bent before forming.

Forming and Welding: The strip is then formed into a spiral shape, and the seam is welded using a welding seam control device to ensure the weld meets stringent requirements. This device also carefully monitors the pipe diameter, alignment, and weld quality.

Quality Inspection: After cutting the spiral into individual steel pipes, a strict first-inspection system is employed for every batch of three pipes. This includes checking mechanical properties, chemical composition, weld fusion, surface quality, and conducting non-destructive inspections to ensure the pipes meet production standards before full-scale production begins.

2. Production Process of Longitudinal Submerged Arc Welded (LSAW) Pipes

LSAW pipes are typically made from steel plates and are formed through different processes before being welded using double-sided submerged arc welding. The process involves:

Equipment and Forming Methods: The primary equipment includes milling machines, pre-bending machines, forming machines, pre-welding machines, and pipe expansion machines. LSAW pipes can be formed through various methods, including UOE (U-shaped, O-shaped, expanded), RB (roll bent), and JCOE (J-shaped, C-shaped, O-shaped, expanded).

Forming and Welding: The steel plate is first pressed into a U shape, then into an O shape, followed by internal and external submerged arc welding. After welding, the pipe diameter is expanded (or not, depending on the method used), resulting in UOE or RB pipes, respectively. In the JCOE method, the steel plate is formed sequentially into J, C, and O shapes before welding and diameter expansion.

3. Production Process of Straight Seam High-Frequency Resistance Welded (ERW) Pipes

Straight seam high-frequency resistance welded pipes (ERW pipes) are formed from hot-rolled coils. The process includes:

Forming: The coil is shaped into a pipe by a forming machine.

Welding: High-frequency current is applied to create a "skin effect" and "proximity effect," heating and melting the edges of the pipe blank. The edges are then pressed together under the action of extrusion rollers, completing the welding and forming the final product.

These methods showcase the diversity in production techniques and applications of welded steel pipes, each suited to specific requirements and industrial uses.