Comparison of technical characteristics of spiral welded steel pipe and straight seam welded steel pipe

Spiral welded steel pipe and straight seam welded steel pipe have different technical characteristics and production processes, and have many differences and distinctions in production. They have different functions and uses, and the value they show in use is also different. The comparison of technical characteristics of spiral welded steel pipe and straight seam welded steel pipe is as follows:

First, the difference in the welding process
In terms of the welding process, the welding method of spiral welded steel pipe and straight seam steel pipe is the same, but straight seam welded steel pipe will inevitably have many T-welds, so the probability of welding defects is greatly improved, and the welding residual stress at the T-weld is large, and the weld metal is often in a triaxial stress state, which increases the possibility of cracks. Moreover, according to the process regulations of submerged arc welding, each weld should have an arc initiation point and an arc extinguishing point, but each straight seam welded steel pipe cannot meet this condition when welding the circumferential seam, so there may be more welding defects at the arc extinguishing point. Therefore, the spiral welded steel pipe produced has good quality assurance to ensure that the products produced will not have defects such as cracks.

Second, the strength characteristics of spiral welded steel pipes and straight seam welded steel pipes
When the steel pipe is subjected to internal pressure, two main stresses are usually generated on the pipe wall, namely radial stress δY and axial stress δX. The composite stress at the weld δ=δY(l/4sin2α+cos2α)1/2, where α is the spiral angle of the spiral welded steel pipe weld. The spiral angle of the spiral welded steel pipe weld is generally 50-75 degrees, so the composite stress at the spiral weld is 60-85% of the main stress of the straight seam welded steel pipe. Under the same working pressure, the wall thickness of the spiral welded steel pipe of the same diameter can be reduced compared with the straight seam welded steel pipe.

Third, the metallurgical properties of spiral welded steel pipe and straight seam welded steel pipe materials
Straight seam submerged arc welded steel pipes are produced from steel plates, while spiral welded steel pipes are produced from hot-rolled coils. The rolling process of the hot-rolled strip steel unit has a series of advantages and has the metallurgical process capability to produce high-quality pipeline steel. For example, a water cooling system is installed on the output stand to accelerate cooling, which allows the use of low alloy components to achieve special strength grades and low-temperature toughness, thereby improving the weldability of steel. However, this system is not available in steel plate production plants. The alloy content (carbon equivalent) of the coil is often lower than that of similar-grade steel plates, which also improves the weldability of spiral welded steel pipes.

It is also necessary to explain that because the coil rolling direction of the spiral welded steel pipe is not perpendicular to the axis of the steel pipe (its clamping solution depends on the helix angle of the steel pipe), and the steel plate rolling direction of the straight seam steel pipe is perpendicular to the axis of the steel pipe, the anti-cracking function of the spiral welded steel pipe material is better than that of the straight seam steel pipe. A systematic comparison of spiral welded steel pipes and straight seam welded steel pipes in the welding process, metallurgical properties, and strength characteristics is carried out, focusing on the analysis of the differences and main differences between the two, and specifically introducing the welding process and method, strength performance, and metallurgical properties and processes of each pipe fitting.