Spiral steel pipe and straight seam welded pipe in production process in terms of the difference on the analysis from the welding process, the spiral welded pipe and straight seam steel pipe welding method is consistent, but the straight seam welded pipe will inevitably have a lot of t-shaped weld, so the probability of weld defects is also greatly improved, and the t-shaped seam welding residual stress is larger, the stress state of the weld metal are often in a three-way increases the possibility of a crack.
In addition, according to the process regulations of submerged arc welding, each welding seam should have arc starting and arc extinguishing places, but each straight seam welding pipe cannot meet this condition when welding circular seam, so there may be more welding defects in the arc extinguishing place.When the pipe is under internal pressure, two main stresses are usually generated on the pipe wall, that is, the radial stress delta and the axial stress delta.The resultant stress at the weld is delta, where is the spiral Angle of the weld of the spiral welded pipe.The spiral Angle of the weld of spiral welded pipe is generally degree, so the synthetic stress at the spiral weld is the main stress of straight welded pipe.
Under the same working pressure, the wall thickness of spiral welded pipe with the same diameter can be reduced than that of straight welded pipe.According to the above characteristics, it can be seen that when the spiral welded pipe is exploded, since the normal stress and synthetic stress on the welding seam are relatively small, the blasting hole generally does not originate from the spiral welding seam, and its safety is higher than that of the straight welded pipe.When there are parallel defects in the vicinity of spiral welds, the risk of expansion of spiral welds is not as great as that of straight welds due to the small force on the spiral welds.Since the radial stress is the maximum stress on the steel pipe, the maximum load is borne when the weld is in the direction of vertical stress.
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