Mechanical properties of different welded pipes

Mechanical properties of different welded pipes

The production process of straight seam welded pipes is relatively simple. The main production processes are electric resistance welded straight seam steel pipe (ERW pipe) and submerged arc welded straight seam steel pipe (LSAW pipe). Straight seam pipes have high production efficiency, low cost and rapid development.

The strength of galvanized spiral welded pipes is generally higher than that of straight seam welded pipes, and the main production process is submerged arc welding. Spiral steel pipe (SSAW pipe) can produce welded pipes of different diameters from billets of the same width, and can also use narrower billets to produce larger diameter welded pipes. However, compared with straight seam pipes of the same length, the weld length is increased by 30~100% and the production speed is lower. Therefore, smaller diameter welded pipes mostly use straight seam welding, and large diameter welded pipes mostly use spiral welding.

Welding process

In terms of welding technology, the welding method of galvanized spiral welded pipes is the same as that of galvanized straight seam steel pipes, but straight seam welded pipes inevitably have many T-shaped welds. Therefore, the probability of welding defects is also greatly increased, and the welding residual stress at the T-shaped weld is relatively large, and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracks.

Static pressure bursting strength

Through relevant comparative tests, it was verified that the measured values and theoretical values of yield pressure and burst pressure of spiral welded pipes and straight seam welded pipes are basically consistent, and the deviations are close. However, whether it is yield pressure or burst pressure, spiral welded pipes are lower than straight seam welded pipes. The blasting test also shows that the circumferential deformation rate of the blasting port of spiral welded pipes is significantly greater than that of straight seam welded pipes. This proves that the plastic deformation ability of spiral welded pipes is better than that of straight seam welded pipes, and the blasting opening is generally limited to one pitch. This is because the spiral welds have a strong constraint on the expansion of the welded pipes. crack.

Toughness and fatigue strength

The development trend of pipelines is large diameter and high strength. As the diameter of the steel pipe increases and the type of steel used increases, the tendency of the ductile fracture tip to expand stably becomes greater. According to tests by relevant research institutions, although spiral welded pipes are at the same level as straight seam welded pipes, spiral welded pipes have higher impact toughness.

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