When the tube is subjected to internal pressure, it usually produces two main stresses on the pipe wall, namely radial stress δY and axial stress δX. The synthetic stress at the weld is δ=δY(l/4sin2α+cos2α)1/2, where α is the helix angle of the spiral welded pipe weld.
The spiral angle of the spiral welded pipe weld is generally 50-75 degrees, so the synthetic stress at the spiral weld is 60-85% of the main stress of the straight welded pipe. Under the same working pressure, the thickness of the spiral welded pipe of the same pipe diameter can be reduced compared with the straight welded pipe.
According to the above characteristics, we can know:
A. When the spiral welded pipe is blasted, since the normal stress and the synthetic stress of the welded joint are relatively small, the blasting hole generally does not originate from the spiral welded joint, and its safety is higher than that of the straight welded pipe.
B. When there is a defect parallel to the spiral weld, since the screw weld is less stressed, the risk of expansion is not as great as that of the straight weld.
C. Since the radial stress is the maximum stress present on the steel pipe, the weld is subjected to the maximum load in the direction of the vertical stress. That is, the straight seam is subjected to the largest load, and the hoop weld is subjected to the least load, and the spiral seam is between the two.
Cangzhou Steel Pipe Group (CSPG)Co.,Ltd.
No.92 JieFang East Road ,Cangzhou City, Hebei,P.R.China.
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