Welded pipe is generally divided into straight-seam welded pipe  and spiral welded pipe two types.

Welding process

From the welding process, the 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 welds, 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 is often in a three-way increases the possibility of a crack. And, according to the regulations of the submerged arc welding process, each weld shall have arc and arc in, but every straight seam welded pipe when weld girth, can not meet the conditions, thus there may be more arc welding defects.

Strength characteristics

When the pressure in the pipe withstands, usually two main stress on the wall, 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, a spiral pipe of the same diameter as the Longitudinal wall thickness can be reduced.

Hydrostatic burst strength

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 is closer. But whether it is the yield stress or burst pressure, were lower than the Longitudinal spiral welded. The burst test also shows that the rate of deformation ring spiral welded pipe bursting Longitudinal is significantly greater than the mouth. This 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.

Toughness and fatigue strength

The trend of the development of the pipeline is of large diameter and high strength. With the increase in 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, the spiral welded pipe is with high impact toughness. In transmission pipelines due to the amount of change in the actual operation, the pipe is subjected to a random alternating load effect.

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