Welded Steel Pipe
Forming Process: Welded steel pipe is formed by directly rolling steel plates or strips through a forming machine into the shape of a straight seam steel pipe. Generally, the flat steel is first edge-processed, such as beveling, and then bent into a cylindrical shape by a press or roller, so that the two sides of the steel plate are aligned to form a straight seam.
Welding method: When welding straight seams, high-frequency straight seam welding (ERW) or submerged arc welding (SAW) is often used. High-frequency straight seam welding uses the resistance heat generated by high-frequency current on the edge of the steel plate to melt the edge and weld it together under pressure. Submerged arc welding is achieved by covering the welding area with flux, allowing the welding wire and steel plate to melt and fuse under the action of the arc. The flux protects the molten pool and participates in metallurgical reactions.
Weld characteristics: A straight weld runs along the longitudinal direction of the steel pipe, resulting in a regular, simple weld shape. High-frequency straight welds result in a relatively small heat-affected zone and a smooth, neat weld appearance. However, since the weld is linear, the stress distribution at the weld is relatively concentrated when subjected to internal pressure, especially in the case of large diameter and high pressure, which places extremely high demands on the weld quality.
Spiral Welded Pipe
Forming Process: Spiral welded pipe is made from a coiled steel strip. At room temperature, the coiled steel strip is formed into a tube blank using a spiral forming machine at a specific angle (helix angle). As the strip steel moves forward continuously, it is curled and welded at the same time, ultimately forming a steel pipe with a spiral weld.
Welding method: The welding mainly employs double-wire double-sided submerged arc welding. Two welding wires are welded on both sides of the steel pipe at the same time. This method can improve welding speed and welding quality. During welding, the arc, under the protection of the flux, melts and combines the welding wire and the edge of the strip to form a continuous spiral weld.
Weld characteristics: Spiral welds are spirally distributed along the steel pipe. Compared to straight seam steel pipe, the stress concentration at the spiral weld is lower under the same pressure. However, the shape of spiral welds is more complex, and it is slightly more difficult to detect and control the quality than straight welds.
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