Comparison of advantages and disadvantages of spiral steel pipe and straight seam steel pipe welding

The welding seam steel pipe of the spiral steel tube is longer than that of the straight-seam steel tube. If the tube length is L, the welding seam length is L/cos(θ). The vast majority of steel pipe defects 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 that restricts the broader application of spiral welded pipes for a long time. Straight seam steel pipes, especially compared with UOE steel pipes, are a question of who is superior. With the development of spiral steel tube manufacturing technology today, we should evaluate and compare comprehensively and correctly, and re-understand the problem of long spiral steel tube welds.

First of all, since the defect is parallel to the weld, for the spiral steel pipe, the defect of the 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, because the pipeline steels are all rolled steel plates, the impact toughness has a large anisotropy. The CVN value along the rolling direction can be three times higher than the CVN value perpendicular to the rolling direction.

The principal stress of the straight seam steel pipe is just perpendicular to the direction of the impact resistance of the pipe, while the spiral steel pipe is staggered in the direction of the impact resistance of the pipe, which turns the disadvantage of the long weld of the spiral steel pipe into an advantage.