The production process of galvanized straight seam welded pipe is relatively simple. The main production processes are 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 the same width blank to produce welded pipes with different diameters, and can also use narrower blanks to produce welded pipes with larger diameters. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower. Therefore, most of the welded pipes with smaller diameters adopt straight seam welding, and most of the large-diameter welded pipes adopt spiral welding. T-welding technology is used in the production of larger diameter straight seam steel pipes in the industry, that is, short straight seam steel pipes are butt-jointed again to form a length that meets the needs of the project. The probability of defects in T-welded straight seam steel pipes 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, which increases the possibility of cracks.
welding process
In terms of the welding process, the welding method of galvanized spiral welded pipe is the same as that of galvanized straight seam steel pipe, but straight seam welded pipe will inevitably have many T-shaped welds, so the probability of welding defects is also greatly increased, and T-shaped welds The welding residual stress is relatively large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracks.
Static pressure burst strength
Through relevant comparative tests, it is verified that the yield pressure of the spiral welded pipe and the longitudinal seam welded pipe are consistent with the measured and theoretical values of the burst pressure, 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 spiral welded pipe blasting opening is significantly greater than that of the straight seam welded pipe. This proves 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 weld on the expansion of the crack. the
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 steel grade used, the tendency of the ductile fracture tip to expand steadily is greater. According to tests conducted by relevant research institutions in the United States, although spiral welded pipes and longitudinal welded pipes are of the same level, spiral welded pipes have 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 resistance welded pipe, and the test data is distributed in the same area as the seamless pipe and the resistance pipe and is higher than that of the general submerged arc welded pipe.
Post time: Jul-31-2023