The difference between spiral welded pipe and straight-seam welded pipe

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2021-01-20

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The primary difference between spiral welded pipe and straight-seam welded pipe lies in their welding processes. Spiral welded pipe is manufactured by rolling low‑carbon structural steel or low‑alloy structural steel strip into a tubular blank at a specific helical angle—also known as the forming angle—and then welding it to form the seam. This method enables the production of large‑diameter pipes from relatively narrow strips. Spiral welded pipe is predominantly represented by spiral submerged‑arc welded pipe (SSAW), which is widely used in China for constructing various gas pipelines. Its dimensions are specified as “outer diameter × wall thickness.” Spiral welded pipes can be either single‑sided or double‑sided welded, and they must meet prescribed requirements for hydrostatic testing, weld tensile strength, and cold‑bend performance.

　　 Spiral welded pipe The primary difference between spiral welded pipe and straight-seam welded pipe lies in their welding configurations. In spiral welded pipe, low‑carbon structural steel or low‑alloy structural steel strip is rolled into a tubular blank at a specific helical angle—also known as the forming angle—and then welded to form the seam. This process enables the production of large‑diameter pipes from relatively narrow steel strips. Spiral welded pipe is predominantly represented by submerged‑arc spiral welded pipe (SSAW), which is widely used in China for constructing various gas pipelines. Pipe dimensions are specified as “outer diameter × wall thickness.” Spiral welded pipes may be single‑sided or double‑sided welded, and they must meet prescribed requirements for hydrostatic testing, weld tensile strength, and cold‑bending performance.

　　Longitudinal seam welded pipe is produced by first forming a coil on a roll‑forming machine, after which the pipe blank undergoes high‑frequency current and proximity‑effect heating to melt the edge material. Under a specified extrusion pressure, the molten edges fuse together, then cool and solidify into the final shape. When the pipe‑blank edges are melted using high‑frequency current, the resulting product is known as electric‑resistance welded (ERW) pipe; when melting is achieved by an electric arc, it is referred to as longitudinal submerged‑arc welded (LSAW) pipe.

　　Spiral welded pipes generally have higher strength than straight-seam welded pipes. Their primary manufacturing process is submerged-arc welding. Spiral welded pipes can produce pipes of varying diameters from billets of the same width and can also manufacture larger-diameter pipes using narrower billets. In contrast, the production process for straight-seam welded pipes is relatively simpler, with two main methods: high-frequency welded straight-seam pipes and submerged-arc welded straight-seam pipes. Straight-seam welded pipes offer high production efficiency, low costs, and rapid development.

　　However, compared with straight-seam welded pipes of the same length, the weld seam length increases by 30% to 100%, and the production speed is lower. Consequently, smaller-diameter welded pipes are mostly manufactured using straight-seam welding, while larger-diameter welded pipes are predominantly produced by spiral welding.

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