1. Welding process
In the welding process, the welding method of the spiral steel pipe and the longitudinal welded pipe is the same, but the longitudinal welded pipe inevitably has many T-shaped welds, so the probability of welding defects is greatly increased, and the welding residual stress at the T-shaped weld is relatively large. , The weld metal is often in a three-dimensional stress state. This increases the possibility of rupture.
In addition, according to the process requirements of submerged arc welding, each weld should have arc ignition and arc extinction. However, in girth welding, each longitudinal welded pipe cannot meet this condition, so it may be possible at the arc extinction. There are more welding defects.
2. Strength characteristics
When the pipeline bears 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 spiral steel pipe weld.
The spiral angle of the spiral steel pipe weld is generally degrees, so the resultant stress at the spiral weld is the principal stress of the longitudinal welded pipe. Under the same working pressure, the wall thickness of spiral welded pipes with the same diameter is smaller than that of straight seam welded pipes.
3. Static explosion strength
The comparative test results show that the yield pressure of the spiral steel pipe and the longitudinally welded pipe is consistent with the actual and theoretical values of the burst pressure, and the deviation is very close. The yield pressure and burst pressure of spiral steel pipes are lower than those of longitudinal welded pipes. The blasting test also showed that the circumferential deformation rate of the spiral welded pipe blasting hole was significantly greater than that of the straight seam welded pipe. The results show that the plastic deformation ability of spiral welded pipe is better than that of straight seam welded pipe. Because spiral welded pipe has a strong inhibitory effect on crack propagation, the blast hole is generally limited to one pitch.