How are high-quality spiral tubes manufactured?

Release date:

2021-02-18

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Steel Pipe Knowledge

We all know that producing high-quality spiral pipes requires not only superior steel but also robust support across all stages of the manufacturing process. Only in this way can we ensure that every spiral pipe meets stringent quality standards. So, what other factors influence the quality of spiral pipes? Let’s take a closer look.

　　We all know that producing high-quality spiral pipes requires not only superior steel but also robust support across all stages of the manufacturing process. Only in this way can we ensure that every spiral pipe meets stringent quality standards. So, what factors influence… Spiral tube What else is there about quality? Let’s take a look.

　　1. Welding temperature: For low-carbon steel, the welding temperature should be maintained within the range of 1250–1460°C to ensure full penetration for pipe wall thicknesses of 3–5 mm. The welding temperature is primarily controlled by adjusting the high-frequency eddy‑current heating power and the welding speed. If the heat input is insufficient, the heated edge of the weld fails to reach the required welding temperature, leaving the metal microstructure in the solid state and resulting in lack of fusion or incomplete penetration. Conversely, excessive heat input causes the heated weld edge to exceed the welding temperature, leading to overheating or droplet formation and the development of porosity in the weld.

　　2. Welding: Spiral pipes are typically manufactured using high-frequency welding, which is an induction welding process (or pressure-contact welding). This method eliminates the need for filler metal, produces no spatter, features a narrow heat-affected zone, yields aesthetically pleasing welds, and delivers excellent mechanical properties. Consequently, it is widely employed in steel pipe production. Based on the principles of electromagnetic induction and the skin effect, proximity effect, and eddy-current heating associated with alternating currents in conductors, the edges of the pipe material are locally heated to a molten state. Subsequent rolling pressure then facilitates crystalline bonding at the joint, achieving a solid weld. After cooling, this results in a strong, straight seam.

　　3. Weld Gap: The strip steel is fed into the pipe‑welding unit, where it is progressively rolled by multiple sets of rollers, causing it to curl and form a circular tube blank with an open gap. By adjusting the downward pressure of the squeeze rolls, the weld gap is maintained within 1–3 mm, ensuring that both ends of the weld are flush. If the gap is too large, the skin effect is reduced, resulting in insufficient eddy‑current heating and poor intergranular bonding at the weld, which may lead to lack of fusion or cracking. Conversely, if the gap is too small, the skin effect intensifies, generating excessive welding heat and causing burn‑through; alternatively, the weld may develop deep depressions after squeezing and rolling, compromising the surface quality of the joint.

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