Comparison of advantages and disadvantages of welded seams between spiral steel pipes and straight seam steel pipes

Comparison of advantages and disadvantages of welded seams between spiral steel pipes and straight seam steel pipes

The weld seam of the spiral steel pipe is longer than that of the straight seam steel pipe. If the pipe length is L, the weld seam length is L/cos(θ). The vast majority of steel pipe defects are concentrated in the weld seam and heat-affected zone. The long weld seam means the probability of occurrence of defects is high. This is the main reason that has restricted the wider application of spiral welded pipe for a long time. Straight seam steel pipe, especially compared with UOE steel pipe, is the question of who is superior.

With the development of spiral steel pipe manufacturing technology today, we should comprehensively and correctly evaluate and compare, and re-understand the problem of long spiral pipe welds.

First of all, because the defect is parallel to the weld, the weld defect of the spiral steel pipe 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, 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 staggers the direction of the pipe's impact resistance, which turns the disadvantage of the spiral steel pipe's weld length into an advantage.