Comparison of galvanized spiral steel pipe, straight seam steel pipe and galvanized seamless steel pipe

The production process of galvanized straight seam welded pipe is relatively simple. The main production processes include high-frequency welded straight seam steel pipe and submerged arc welded straight seam steel pipe. Straight seam pipe has high production efficiency, low cost, and rapid development. The strength of galvanized spiral welded pipe is generally higher than that of straight seam welded pipe. The main production process is submerged arc welding. Spiral steel pipe can use blanks of the same width to produce welded pipes with different diameters, and can also use narrower blanks to produce welded pipes with larger diameters. . However, compared with the same length of straight seam pipe, the length of the weld is increased by 30~100%, and the production speed is lower. Therefore, most of the welded pipes with smaller diameters use straight seam welding, and most of the welded pipes with large diameters use spiral welding. T-welding technology is used in the production of large-diameter straight-seam steel pipes in the industry, that is, short sections of straight-seam steel pipes are butted together to form a length that meets the needs of the project. The welding residual stress at the seam is large, and the weld metal is often in a three-way stress state, which increases the possibility of cracks.

welding process

In terms of the welding process, the welding method of galvanized spiral welded pipe and galvanized straight seam steel pipe is the same, but the straight seam welded pipe will inevitably have many T-shaped welds, so the probability of welding defects is also greatly improved, and the T-shaped welded seam The welding residual stress at the weld is relatively large, and the weld metal is often in a state of three-dimensional stress, which increases the possibility of cracks.

Static Bursting Strength

Through the relevant comparative tests, it is verified that the yield pressure and the burst pressure of the spiral welded pipe and the straight seam welded pipe are consistent with the measured value and the theoretical value, and the deviation is close. But whether it is yield pressure or burst pressure, the spiral welded pipe is lower than the straight seam welded pipe. The blasting test also shows that the circumferential deformation rate of the blasting opening of the spiral welded pipe is significantly greater than that of the straight seam welded pipe. It is confirmed that the plastic deformation ability of the spiral welded pipe is better than that of the straight seam welded pipe, and the blasting opening is generally limited to one pitch, which is due to the strong restraint effect of the spiral welded seam on the expansion of the crack.

toughness and fatigue strength

The trend of pipeline development is large diameter and high strength. With the increase of the diameter of the steel pipe and the improvement of the grade of steel used, the tendency of the ductile fracture tip to expand steadily is greater. According to the test of relevant research institutions in the United States, although the spiral welded pipe and the straight seam welded pipe are of the same level, the spiral welded pipe has higher impact toughness.

According to the measurement results, the fatigue strength of the galvanized spiral welded pipe is the same as that of the galvanized seamless pipe and the electric resistance welded pipe.