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 large, and the weld metal is often in a three-dimensional stress state. This increases the likelihood of breakage. In addition, according to the technical requirements of submerged arc welding, each weld should have arc initiation and arc extinction, but in the case of circular seam welding, each
straight seam welded pipe cannot meet this condition, so it may be possible at the arc extinguishing point. There are more welding defects.
2. Strength characteristics. When the pipeline is subjected to internal pressure, there are usually two main stresses on the wall surface, 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
spiral steel pipe weld is generally degrees, so the resultant stress at the spiral weld is the principal stress of the
straight seam welded pipe. Under the same working pressure, the wall thickness of the spiral welded pipe of 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
straight seam welded pipe are basically 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 propagation, the blasting hole is generally limited within a pitch.
