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Spiral Steel Pipe Experiment Inspection

Update:2017-03-10   View(s):1530   Keywords :SSAW steel pipe ,Welded pipe
From the welding process, the spiral seam steel pipe and welding straight line, but inevitably there will be a lot of Longitudinal T-weld, so the probability of the existence of welded pipe defects has greatly improved, and T-welds the weld large residual stress, weld metal are often in three dimensional stress state, increasing the possibility of cracks.
Moreover, according to the provisions of submerged arc welding process, and each shall have the weld arc and extinction at the office, but each ring Longitudinal seam welding, you can not meet the conditions, which may be in the extinction at have more of welding defects. Tube to withstand internal pressure, usually resulting in the two main stress on the wall, δ is the radial stress and axial stress δ. The synthesis of the weld stress δ, which, α is the helix angle of spiral weld pipe. SSAW steel pipe is generally degree helix angle, so the synthesis of spiral weld Longitudinal stress is the main stress. In the same work under the pressure of the same diameter spiral welded pipe wall thickness can be reduced compared Longitudinal.

Based on the above characteristics we can see: spiral welded pipe explosion occurred, because the weld is stress and resultant stress suffered relatively small, I generally do not blast originated in the spiral weld, Longitudinal higher than their safety. When the existence of spiral weld near parallel with defects, due to the smaller spiral weld force, so the risk of expansion of weld straight as large. As the radial stress is present in the maximum stress on the pipe, so the seam in a vertical direction to withstand the stress of the maximum load. Straight seam that bear the largest load, the load ring to the weld to withstand the minimum, spiral seam between. 

Hydrostatic burst strength by the comparison test to verify thespiral pipe and Longitudinal yield pressure and burst pressure measured and theoretical values are basically consistent, deviation close. But whether it is the yield pressure or burst pressure, spiral welded pipe are lower than the Longitudinal. Blasting tests also show ring spiral welded pipe to the mouth of the blast was significantly larger than the Longitudinal deformation. Thus confirmed that the spiral welded pipe is superior to the plastic deformation capacity Longitudinal, population explosion generally confined to within a pitch, which is the spiral seam of the expansion gap played a strong role in binding caused by. Toughness and fatigue strength of pipeline development trend of large diameter, high strength. With the increased pipe diameter, the steel grade increase, resulting in ductile fracture tip steady trend of greater expansion. According to the U.S. for research experiments have shown that spiral welded pipe and Longitudinal although the same as a level, but the spiral welded pipe has a high impact toughness.

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