Weld Seam Treatment and Process Characteristics of Spiral Welded Steel Pipes

Release date:

2016-10-11

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Steel Pipe Knowledge

Spiral welded steel pipe is produced by feeding strip steel into a welding line. As it passes through multiple sets of rollers, the strip gradually curls up to form a circular tube blank with an open seam. The gap between the weld edges is adjusted by regulating the downward pressure of the squeeze rolls, keeping it within 1–3 mm and ensuring that both ends of the weld are flush. 1. If the gap is too large, the proximity effect diminishes, resulting in insufficient eddy‑current heating and poor intergranular bonding at the weld, which may lead to lack of fusion or cracking. 2. If the gap is too small, the proximity effect intensifies, generating excessive heat and causing burn‑through at the weld; alternatively, the weld may develop deep pits after squeezing and rolling, adversely affecting surface quality. After heating both edges of the tube blank to the welding temperature, the squeeze rolls compress them, promoting mutual penetration and crystallization of the metal grains, ultimately forming a strong, reliable weld. For spiral welded pipes, insufficient squeezing results in fewer shared crystals, reducing weld strength and increasing susceptibility to cracking under load. Conversely, excessive squeezing can force molten metal out of the weld, not only weakening the joint but also producing significant internal and external burrs and even leading to defects such as lap joints. Key features of the spiral welded pipe manufacturing process: 1. Raw materials—including coil steel, welding wire, and flux—are subjected to rigorous physicochemical testing prior to use. 2. Before forming, the strip steel undergoes leveling, edge trimming, edge planing, surface cleaning, conveying, and pre‑bending operations. 3. During forming, the steel plate deforms uniformly, residual stresses remain low, and no surface scratches occur. This process offers greater flexibility in diameter and wall‑thickness dimensions, providing distinct advantages—particularly for high‑grade thick‑walled pipes, especially small and medium diameters—that other methods cannot match, thereby meeting diverse customer requirements for spiral pipe specifications. 4. Advanced double‑sided submerged‑arc welding ensures optimal positioning, minimizing misalignment, weld偏shift, and incomplete penetration, while facilitating precise control over weld quality. 5. A weld‑gap control device guarantees that the weld gap meets specified requirements, with strict oversight of pipe diameter, edge misalignment, and weld‑gap tolerances. 6. Each pipe undergoes 100% quality inspection, ensuring that the entire production process remains under effective monitoring and testing, thus safeguarding product quality. 7. All equipment along the production line is equipped with network connectivity to a computerized data‑acquisition system, enabling real-time data transmission and centralized monitoring of process parameters from the central control room.

The spiral steel pipe line feeds the strip steel into the welded pipe mill, where it is progressively rolled by multiple sets of rollers, causing the strip to curl and form a circular tube blank with an open seam. By adjusting the penetration of the squeeze rolls, the weld gap is maintained within 1–3 mm, and the two ends of the weld are brought into flush alignment.

1. If the gap is too large, the proximity effect is reduced, 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 increases, leading to excessive welding heat and burn‑through of the weld; alternatively, after extrusion or roll‑forming, the weld may develop deep pits, compromising its surface quality.

After heating the two edges of the tube blank to the welding temperature, the extrusion rollers press them together, causing the metal grains to interpenetrate and recrystallize, ultimately forming a strong weld. For spiral welded pipes, if the extrusion force is too low, fewer common crystals form, resulting in reduced weld strength and susceptibility to cracking under load; conversely, excessive extrusion force can squeeze molten metal out of the weld, not only diminishing weld strength but also generating substantial internal and external burrs and potentially leading to defects such as weld overlap.

Characteristics of the spiral steel pipe manufacturing process:

1. The raw materials—steel strip coils, welding wire, and flux—are all subjected to rigorous physicochemical testing prior to use.

2. Prior to forming, the strip steel undergoes leveling, edge trimming, edge planing, surface cleaning and conveying, and pre‑bending of the edges.

3. During the forming process, the steel plate undergoes uniform deformation, exhibits low residual stress, and remains free of surface scratches. The fabricated spiral welded pipes offer greater flexibility in diameter and wall‑thickness dimensions, particularly excelling in the production of high‑grade thick‑walled pipes—especially small and medium‑diameter thick‑walled pipes—providing advantages unmatched by other manufacturing processes and enabling compliance with a wider range of customer specifications.

4. Employing advanced double-sided submerged arc welding, this process enables welding at the optimal position, minimizing defects such as edge misalignment, weld misalignment, and incomplete penetration, thereby facilitating precise control of weld quality.

5. A weld gap control device is employed to ensure that the weld gap meets welding requirements, with strict control over pipe diameter, misalignment, and weld gap.

6. Steel pipes undergo 100% quality inspection, ensuring that the entire production process is under effective testing and monitoring, thereby effectively guaranteeing product quality.

7. All equipment on the entire production line is equipped with network connectivity to the computer-based data acquisition system, enabling real-time data transmission and allowing the central control room to monitor and manage process‑related technical parameters.

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