Welded pipe is generally divided into straight seam welded pipe and spiral welded pipe two types.
From the welding process, Welding method of the spiral welded pipe and straight seam steel pipe 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. And, according to the regulations of submerged arc welding process, each weld shall have arc and arc in, but every straight seam welded pipe when weld girth, cannot meet the conditions, thus there may be more at arc welding defects.
When the pressure in the pipe withstand, usually two main stress on the wall, that the radial and axial stress δ. Synthetic weld stress δ, where α is the helix angle of the spiral weld pipe. Spiral welded seam degree helix angle is generally so synthetic, and spiral weld longitudinal stress is the main stress. Under the same operating pressure, spiral pipe of the same diameter than the longitudinal wall thickness can be reduced.
By the relevant comparison test to verify the spiral welded pipe and Longitudinal yield pressure and burst pressure measured and theoretical values ​​match, the deviation closer. But whether it is the yield stress or burst pressure, were lower than the longitudinal spiral welded. Burst test also shows that the rate of deformation ring spiral welded pipe bursting Longitudinal significantly greater than the mouth. Thus confirmed that the spiral welded plastic deformation capability than Longitudinal, blasting mouth generally confined to a pitch, which is the extension of the spiral weld to rip from a strong binding effect due.
The trend of the development of the pipeline is of large diameter and high strength. With the increase of the diameter of the pipe and the steel grade increases, the greater the ductile fracture tip steady expansion trend. Although spiral welded pipe and straight seam welded pipe has the same level, spiral welded pipe is with high impact toughness. Transmission pipelines due to the amount of change in the actual operation, the pipe is subjected to random alternating load effect.