Comparison of the advantages and disadvantages of spiral steel pipe and straight seam steel pipe welds

The weld of spiral steel pipe is longer than that of straight seam steel pipe. If the pipe length is L, the weld length is L/cos(θ). Most of the defects of steel pipes are concentrated in the weld and heat-affected zone. The long weld means that the probability of defects is high. This is the main reason for the long-term restriction of the wider application of spiral welded pipes. There is also a long-standing debate about which is better spiral steel pipes and straight seam steel pipes, especially compared with UOE steel pipes.

With the development of spiral steel pipe manufacturing technology to this day, we should comprehensively and correctly evaluate compare, and re-understand the problem of longer welds of spiral steel pipes.

First of all, since the defect is parallel to the weld, for spiral steel pipes, the defect of its weld is an "oblique defect". During use, the principal stress direction of the steel pipe, that is, the equivalent defect length in the axial direction of the steel pipe is smaller than that of the straight seam steel pipe;

Secondly, since pipeline steel is all rolled steel plates, the impact toughness has a large anisotropy, and the CVN value along the rolling direction can be 3 times higher than the CVN value perpendicular to the rolling direction.

The principal stress of the straight seam steel pipe is exactly perpendicular to the direction of the pipe's impact resistance, while the spiral steel pipe is staggered in the direction of the pipe's impact resistance, turning the disadvantage of the spiral steel pipe's long weld into an advantage.