Commonly used steel pipe introduction -
spiral submerged arc welded steel pipe The strip steel is bent into a spiral shape, and the inner seam and outer seam are welded by submerged arc automatic welding to form a spiral seam steel pipe. It can be widely used in the production of large-diameter steel pipes for the following reasons:
1) As long as the forming angle is changed, the steel strip of the same width can be used to produce steel pipes of various diameters;
2) Because it is continuous bending, the length of the steel pipe is not limited;
3) The welds are spirally evenly distributed on the entire circumference of the steel pipe, so the steel pipe has high dimensional accuracy and high strength;
4) The cost of equipment is cheap, and the size is easy to change, which is suitable for the production of small batches and various types of steel pipes.
The weld seam of the spiral pipe is longer than that of the straight seam pipe. If the pipe length is L, the length of the weld seam is L/cos(θ). However, most of the defects of steel pipes are concentrated in the weld seam and the heat-affected zone. The long weld seam means that the probability of defects is high. This is the main reason for restricting the broader application of spiral welded pipes for a long time, and it is also the long-term debate between spiral pipes and pipes. Straight seam pipe, especially the question of who is superior to UOE steel pipe. Spiral pipe manufacturing technology has developed to this day, we should evaluate and compare comprehensively and correctly, and re-understand the problem of the long weld seam of spiral pipe. First of all, because the defect is parallel to the weld, the defect of the weld is an "oblique defect" for the spiral pipe. In the process of 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 pipe; secondly, because the pipeline steel is rolled steel plate, the impact toughness has a large anisotropy, along the rolling direction The CVN value can be 3 times higher than the CVN value perpendicular to the rolling direction. The main stress of the straight seam pipe is just perpendicular to the direction of the lowest impact resistance of the line, while the spiral pipe staggers the direction of the lowest impact resistance of the tube, turning the disadvantage of the long weld seam of the spiral pipe into an advantage.
