An Overview of Welded Pipe Technology
Welded pipes are categorized based on their forming process into spiral welded pipes and straight seam welded pipes. Additionally, they can be classified by the welding method into high-frequency resistance welding (ERW) and submerged arc welding (SAW). Spiral welded pipes exclusively use submerged arc welding technology. On the other hand, straight seam welded pipes that use submerged arc welding are commonly known as UOE pipes, while those made using high-frequency resistance welding are referred to as ERW pipes.Straight seam submerged arc welded pipes (UOE) employ a post-weld cold expansion process to increase the pipe's diameter, ensuring more precise geometric dimensions. When these pipes are joined, the quality of the joint is excellent, and the welding reliability is ensured. This process also helps eliminate some internal stresses. Moreover, multi-wire welding techniques—such as three or four wires—are often used during the welding of UOE pipes. This method reduces heat input and minimizes the impact on the heat-affected zone of the base material. The first wire in the multi-wire process can help relieve welding-induced stress, further enhancing the mechanical properties of the pipe. Compared to spiral welded pipes, straight seam submerged arc welded pipes have shorter welds, resulting in fewer welding defects and less susceptibility to damage. For high-pressure pipelines, the base material of straight-seam pipes can be fully inspected using 100% ultrasonic testing, meeting strict quality requirements. However, despite the superior performance of UOE pipes, their higher cost may limit their use for projects with tight budgets. Spiral welded pipes feature welds arranged in a helical pattern. Generally, the weld area includes the heat-affected zone, which has inferior mechanical properties compared to the base material. The maximum internal stress in pressure pipes typically occurs along the axial direction, making spiral welded pipes weaker in that region. By positioning the welds away from the direction of maximum stress, the structural performance of the pipe is enhanced. Additionally, the shape and height of the weld seams on spiral pipes can complicate external anti-corrosion treatments. There may even be gaps between adjacent welds. To address this issue, some manufacturers now use horizontal winding techniques to apply three layers of polyethylene (PE) or two layers of PE. This method effectively solves the corrosion problem associated with spiral welded pipes.
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