1. Welding process: In the welding process, the welding method of the spiral steel pipe and the straight seam welded pipe is the same, but the straight seam welded pipe will inevitably have many T-shaped welds, so the probability of welding defects is greatly increased. The welding residual stress is relatively large, and the weld metal is often in a three-dimensional stress state. This increases the likelihood of rupture. In addition, according to the technical requirements of submerged arc welding, each weld should have an arc start and arc extinguishing place, but in circular seam welding, each straight seam welded pipe cannot meet this condition, so the arc extinguishing place may There are more welding defects.
2. Strength characteristics: When the pipe is subjected to internal pressure, its wall usually has two main stresses, namely radial stress and axial stress. The resultant stress at the weld is δ, where α is the helix angle of the weld of the spiral steel pipe. The helix angle of the welded seam of the spiral steel pipe is generally 100 degrees, so the synthetic stress at the spiral welded seam is the main stress of the straight seam welded pipe. Under the same working pressure, the wall thickness of the spiral welded pipe with the same diameter is smaller than that of the straight seam welded pipe.
3. Static explosion strength: The comparative test results show that the yield pressure of the spiral steel pipe and the longitudinal seam welded pipe are consistent with the measured and theoretical values of the burst pressure, and the deviation is very close. The yield pressure and burst pressure of the spiral steel pipe are lower than those of the straight seam welded pipe. The blasting test also shows that the circumferential deformation rate of the blast hole of the spiral welded pipe is significantly larger than that of the straight seam welded pipe. The results show that the plastic deformation ability of the spiral welded pipe is better than that of the straight seam welded pipe. Because the spiral welded pipe has a strong inhibitory effect on crack growth, the blast holes are generally limited to one pitch.