How are welded steel pipes processed?

Generally, there are two types of steel pipes: seamless steel pipes andwelded steel pipes, depending on the production method. Welded pipes, also known as welded steel pipes, are created by welding steel plates or strips that have been curled and shaped. The length typically measures six meters. The production process for welded steel pipes is uncomplicated, yielding high production efficiency and a broad range of variants and specifications while requiring low equipment investment. However, their overall strength is inferior to that of seamless steel pipes. How, then, are welded steel pipes processed? Below we provide a detailed introduction from a carbon steel pipemanufacturer.

Seamed steel pipes are formed by bending a pipe blank, made of steel plate and strip, into the desired cross-sectional shape and size using various forming methods. The welds are then welded together using different welding techniques to produce welded steel pipes. This is the process of manufacturing steel pipes. Compared to seamless steel pipes, welded steel pipes offer higher product accuracy, especially in terms of wall thickness. They also require simpler main equipment, occupy less floor space, allow for continuous production, offer production flexibility, and enable a wider range of unit products.

Welded pipes should be divided into three categories based on production technology: spiral submerged arc welded pipes; straight seam double-sided submerged arc welded pipes; straight seam high-frequency resistance welded pipes.

1. The production process of spiral steel pipe is roughly as follows

The raw materials for manufacturing spiral steel pipes comprise steel strip coil, welding wire and flux.

Prior to the forming process, the steel strip is levelled, trimmed, cleaned and transported, and pre-bent.

To ensure compliance with welding requirements and strict control of pipe diameter, misalignment amount, and welding seam, a welding seam control device is utilized. After being cut into individual steel pipes, batches of three must undergo a rigorous initial inspection process to verify their mechanical properties, chemical composition, weld fusion status, and steel pipe surface quality. Non-destructive testing must also be performed to ensure the pipe manufacturing process is certified prior to being officially put into production.

2. Long seam submerged arc welded pipe

Longitudinal submerged arc welded pipes are typically produced using steel plates. These welded pipes are formed via double-sided submerged arc welding and post-weld diameter expansion, following a variety of shaping processes.

Essential machinery includes milling machines, pre-bending machines, forming machines, pre-welding machines, and pipe expansion machines. The LSAW pipes can be formed using a range of methods including UO (UOE), RB (RBE), and JCO (JCOE). The steel plate is initially pressed into a U shape and then into an O shape using a forming mould. Submerged arc welding is then carried out both internally and externally. Once welding is completed, the diameter (expansion) is commonly referred to as the end or full length of UOE welded pipeline, resulting in UO welded pipe. Following this, the roll bent steel plates undergo submerged arc welding, and the diameter is enlarged to create RBE welded pipe or not RB welded pipe as per requirements. The steel plate undergoes J-type, C-type, and O-type forming processes before being welded. Subsequently, the welded structure is expanded to form either a JCOE welded pipe or a non-JCO welded steel pipe, depending on the specifications.

Straight seam high-frequency resistance welded pipe (ERW pipe) is a hot-rolled coil that a forming machine shapes. The edges of the pipe blank are heated and melted using the skin effect and proximity effect of high-frequency current, before pressure is applied using the extrusion roller. Welding is utilized to achieve the production of the final product.