Tensile strength of the spiral welded pipe

Tensile strength characteristics

Pipe withstand the internal pressure, usually in the wall on the two main stress, radial stress δY and axial stress δX. Weld resultant stress δ = δY (l/4sin2α + cos2α) 1/2, which, α is the helix angle of the spiral weld pipe. Helix angle of the spiral weld pipe is generally 50-75 degrees, so the spiral weld resultant stress in 60-85% of the Longitudinal principal stress. In the same work under the pressure of the same diameter spiral welded straight seam welded pipe wall thickness can be reduced. Based on the above characteristics are known: 
A. spiral welded pipe blast the weld suffered stress and the resultant stress is relatively small, blasting the mouth is generally not originated in the spiral weld, its security Longitudinal. 
B. When the spiral weld near the defect with parallel, spiral weld force is smaller, so the risk of expansion not as good as straight weld large. 
C. Because the radial stress is the maximum stress in the pipe, the weld in the vertical stress is in this direction when under maximum load. To bear the load of the ring to weld the straight seam to bear the load, the spiral in between. 
Static pressure bursting strength 
Verified by the comparison test, spiral welded pipe and Longitudinal yield pressure burst pressure measured and theoretical values, close to the deviation. But whether it is the yield pressure or burst pressure, spiral welded pipe are lower than longitudinally welded pipes. Blasting tests also shows spiral welded pipe blasting the mouth of the circumferential deformation rate was significantly greater than the Longitudinal This confirmed that the plastic deformation of the spiral welded pipe than Longitudinal, blasting the mouth is generally confined to a pitch, spiral weld the expansion of the gap from the strong constraints. 
Toughness and fatigue strength 
The development trend of the pipeline is the large-diameter, high strength. With the increase of pipe diameter, steel grade increase, resulting in greater the ductile fracture tip steady expansion trend. According to test the relevant research institutions in the United States, shown that the spiral welded pipe and Longitudinal is the same as a level, but the spiral welded pipe has a high impact toughness. Pipelines to lose the amount of change in the actual operation, the steel pipe to withstand random alternating load. For the low cycle fatigue strength of the steel pipe, is of great significance to determine the service life of the pipeline. 
According to measurement results, the fatigue strength of the spiral welded pipe and seamless pipe and resistance welding pipe is the same, and the test data of seamless pipe and resistance tube located in the same district, but higher than the average submerged arc Longitudinal.