The difference between the straight seam steel pipe and spiral steel pipe. The production process of longitudinally welded pipe is relatively simple. The main production processes are high-frequency welded longitudinally welded pipe and submerged arc welded longitudinally welded pipe. The longitudinally welded pipe has high production efficiency, low cost, and rapid development. The strength of the spiral welded pipe is generally higher than that of a straight seam welded pipe. The main production process is submerged arc welding. Spiral steel pipe can produce welded pipes with different pipe diameters from the same width of blanks, and can also use narrower blanks to produce welded pipes with larger pipe diameters. However, 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 smaller diameter welded pipes adopted straight seam welding, and the large diameter welded pipes mostly adopted spiral welding. T-welding technology is used in the production of larger diameter longitudinal seam steel pipes in the industry, which means that short sections of longitudinal seam steel pipes are butt-joined to a length that meets the needs of the project. The probability of defects in the T-welded longitudinal seam steel pipe is greatly increased, and the 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.