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 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 greater. The weld metal is often in a three-dimensional state of stress. This increases the possibility of rupture.
In addition, according to the technical requirements of submerged arc welding, each welding seam should have a pilot arc and arc extinction, but in girth welding, each straight seam welded pipe can not meet this condition. Therefore, there may be more welding defects at the arc extinction.
2. Strength characteristics
When the pipeline is under internal pressure, its wall surface usually has two main stresses, namely radial stress and axial stress.
The spiral angle of the spiral steel pipe weld is generally degree, so the synthetic stress at the spiral weld is the main stress of the straight 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 welded pipe.
3. Static explosion intensity
The comparison 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 spiral steel pipe are lower than that of 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 blast hole is generally limited to a pitch.