The weld seam of spiral steel pipe is longer than that of straight seam steel pipe. If the pipe length is L, the weld seam length is L/cos(θ). Most of the defects in steel pipes are concentrated in the welds and heat-affected zones. Long welds mean a high probability of defects. This is the main reason that has long restricted the wider application of spiral welded pipes. It is also the long-standing debate between spiral steel pipes and spiral welded pipes. Straight seam steel pipes, especially the question of who is superior compared with UOE steel pipes.
First of all, because the defects are parallel to the weld, for spiral steel pipes, the defects in the weld are “oblique defects”. During use, the main stress direction of the steel pipe, that is, the equivalent defect length in the axis direction of the steel pipe, is smaller than that of the straight seam pipe;
Secondly, since pipeline steels are all rolled steel plates, the impact toughness has large anisotropy, and the CVN value along the rolling direction can be three times higher than the CVN value perpendicular to the rolling direction.
The principal stress on 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, turning the disadvantage of a long weld seam of spiral steel pipe into an advantage.
Post time: Oct-17-2023