The spiral steel pipe feeds the strip steel into the welded pipe unit. After rolling in multiple rollers, the strip steel is gradually rolled up to form a round tube bank with an open gap. The reduction of the squeeze roller is adjusted to control the weld gap at 1~ 3mm and make both ends of the welding joint flush.

1. If the gap is too large, the proximity effect will be reduced, the eddy current heat will be insufficient, and the weld will not be fused or cracked due to poor intercrystalline joints.

2. If the gap is too small, the proximity effect will increase, and the welding heat will be too large, causing the weld to burn; or the weld will form a deep pit after being extruded and rolled, which will affect the surface quality of the weld.

After the two edges of the tube blank are heated to the welding temperature, under the squeeze of the squeeze roller, a common metal crystal grain is formed to infiltrate and crystallize each other, and finally, a firm weld is formed. If the extrusion force of the spiral steel pipe is too small, the number of common crystals formed will be small, the weld metal strength will decrease, and cracks will occur after the force is applied; if the extrusion force is too large, the molten metal will be squeezed out of the weld. Not only reduces the strength of the weld, but also produces a large number of internal and external burrs, and even causes defects such as weld overlap.