Comparison of galvanized spiral steel pipes, straight seam steel pipes, and galvanized seamless stee

The production process of galvanized straight seam welded pipe is relatively simple. The main production processes include high-frequency welding straight seam steel pipe and submerged arc welding straight seam steel pipe. Straight seam pipe has 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. The main production process is submerged arc welding. Spiral steel pipes can use billets of the same width to produce welded pipes with different diameters, and narrower billets can also be used to produce welded pipes with larger diameters. 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, while large diameter welded pipes mostly use spiral welding. In the industry, T-welding technology is used when producing larger-diameter straight-seam steel pipes. That is, short sections of straight-seam steel pipes are butted together to a length that meets the needs of the project. The probability of T-weld straight-seam steel pipe defects is also greatly increased, and T-welding The welding residual stress at the seam is relatively large, and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracks.

Welding process: In terms of the welding process, the welding methods of galvanized spiral welded pipes and galvanized straight seam steel pipes are the same, but straight seam welded pipes will inevitably have many T-shaped welds, so 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 has been verified that the yield pressure and burst pressure of spiral welded pipes and straight seam welded pipes are consistent with the measured values and theoretical values, 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 blast hole of the spiral welded pipe is significantly greater than that of the straight seam welded pipe. This confirms that the plastic deformation ability of spiral welded pipes is better than that of straight seam welded pipes, and the blast opening is generally limited to one pitch. This is because the spiral welds play a strong role in constraining the expansion of the 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 grade of steel used increases, the tendency of the ductile fracture tip to expand steadily increases. According to tests conducted by relevant research institutions in the United States, although spiral welded pipes and straight seam welded pipes are of the same level, spiral welded pipes have higher impact toughness.

According to the measurement results, the fatigue strength of galvanized spiral welded pipes is the same as that of galvanized seamless pipes and resistance welded pipes. The test data are distributed in the same area as seamless pipes and resistance pipes but are higher than ordinary submerged arc straight seam welded pipes.