1, along the spiral tube in different directions to take samples for tensile testing and impact testing, found that the yield limit and strength limit of the test in different directions is very small difference, generally only in the range of 5-10%, while the cvn value of different directions of specimens vary greatly, cvn value completely with the angle and change.
Although the difference between the yield limit and strength limit along the different directions of the spiral pipe is very small, showing a very slight anisotropy of strength, however, the cvn values along the different directions are very different, that is, the anisotropy of impact toughness is very serious, the consequences of this serious anisotropy of cvn values are different resistance to fracture along the different directions: the straight direction of rolling, that is, the same direction as the spiral weld The fracture resistance is the smallest, that is, easy to crack along this direction; vertical rolling direction fracture resistance is the largest; along the axial direction, the fracture resistance between the two.
2, for the pipeline, the maximum principal stress is the circumferential stress, that is, the maximum drive cracking direction is along the axial. In other words, purely from the stress condition, the original defect is most likely to crack along the axial direction. For straight seam pipes, the direction of maximum driving cracking is the same as the direction of minimum fracture resistance, so the fracture must be along the axial direction. However, for the spiral pipe, the two are not consistent.
3, the direction of fracture expansion of the spiral pipe depends on the size of the spiral pipe for the CVN value of anisotropy.
4, the defects in the welded pipe in the parent material is rarely found, generally in the weld or heat-affected zone, and most of the defects in the weld or heat-affected zone is consistent with the direction of the weld, that is, the direction of the defects in the straight seam pipe for the axial, spiral pipe defects for the oblique. Spiral pipe is more prone to rust, in the process of use should be frequently maintained.