Spiral Steel Pipe Production Process and Welding Technology

Release date:

2022-05-09

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Spiral welded steel pipe is manufactured from strip steel or coiled sheet through a cold-forming process, featuring a helical weld. It is suitable for pressures up to 25 kg. For pipelines operating at pressures exceeding 25 kg, seamless steel pipes or straight-seam submerged-arc welded steel pipes are typically used.

　　 Spiral steel pipe These are steel pipes with helical welds, manufactured through cold forming of steel strips or coil plates, and are suitable for pressures up to 25 kg. For pipelines operating at pressures exceeding 25 kg, seamless steel pipes or longitudinal submerged-arc-welded steel pipes are typically used.

　　Spiral steel pipe production process:

　　First, a re‑inspection is conducted to verify the chemical composition and mechanical properties of the raw materials, ensuring that any missing material meets national standards. Once the materials pass inspection, the steel strip is leveled on an uncoiler, after which the flat sheet enters an edge‑milling machine for beveling the spiral seam prior to welding, thereby enhancing weld quality. The milled plates are then fed into a forming machine to produce the required dimensions, followed by welding of the spiral seam using internal and external submerged‑arc welding equipment. During welding, the flux must be dry and clean, as this directly affects weld quality. Finally, the welded spiral steel pipes are cut into individual sections, typically 12 meters in length.

　　The cut spiral steel pipes shall undergo X-ray inspection to ensure weld quality. Following acceptance of the X-ray examination, groove preparation is performed. After groove preparation, a 20‑kg hydrostatic pressure test is conducted to further verify weld integrity. Upon passing the hydrostatic test, the pipes are transferred to the finished‑goods warehouse in preparation for shipment.

　　Spiral steel pipe welding process:

　　1. Excessive gap size reduces the proximity effect, resulting in insufficient eddy current heating and poor intergranular bonding in the weld, which can lead to lack of fusion or cracking.

　　2. If the gap is too small, the proximity effect intensifies, leading to excessive heat input and weld damage; alternatively, after squeeze rolling, the weld may develop deep depressions, compromising its surface quality.

　　After the two edges of the tube blank are heated to the welding temperature, they undergo interpenetration and crystallization of ordinary metal grains under the squeezing action of the extrusion rollers, thereby forming a strong weld. If the extrusion force applied to the spiral steel pipe is too low, the amount of eutectic phases will be insufficient, leading to a reduction in the strength of the weld metal and eventual cracking under load. Conversely, excessive extrusion pressure can squeeze molten metal out of the weld, not only diminishing weld strength but also generating substantial internal and external burrs and potentially causing defects such as overlapping welds.

A Brief Discussion on the Market Prospects of Spiral Welded Steel Pipes

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