Welding treatment of spiral steel pipe

The production of spiral steel pipes begins by feeding strip steel into a welded pipe unit. As the strip passes through a series of rollers, it gradually forms a tube with an open seam. The squeeze roller’s adjustment controls the size of the weld gap, typically kept between 1–3 mm, ensuring that both ends of the welding joint align properly. The precise control of this gap is critical for the quality of the weld.

Effects of an Oversized Gap

If the gap is too large, the proximity effect (which helps heat the metal) is reduced, leading to insufficient eddy current heat. This can result in the weld not fusing properly or even cracking due to poor bonding at the intercrystalline level.

Effects of an Undersized Gap

If the gap is too small, the proximity effect increases, generating excessive heat. This can cause the weld to burn, or the weld may develop deep pits after extrusion and rolling, negatively impacting the surface quality of the weld.

Once the edges of the tube blank are heated to the appropriate welding temperature, the squeeze roller applies pressure, causing the metal's crystal grains to interpenetrate and crystallize together, forming a strong weld. The pressure applied by the squeeze roller plays a crucial role in the strength of the weld.

- Insufficient Extrusion Force: If the extrusion force is too weak, fewer common metal crystals will form, leading to weaker weld strength. This can result in cracks under stress.

- Excessive Extrusion Force: Conversely, if the extrusion force is too strong, the molten metal may be squeezed out of the weld area. This not only weakens the weld but also creates internal and external burrs and can lead to defects such as weld overlap.

In summary, controlling the welding parameters—especially the gap size and extrusion force—is vital for producing a strong, high-quality weld in spiral steel pipes. Ensuring the right balance in these factors will prevent defects and ensure the weld's integrity under operational stress.