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

Spiral welded pipe and straight-seam welded pipe have different technical characteristics and production processes. There are many differences and differences in production, different functions and uses, and different values in use. . Below, we make a simple comparison of the technical characteristics of the spiral welded pipe and the straight seam welded pipe:

The first is the difference in the welding process

In terms of the welding process, the welding method of spiral welded pipe and straight seam steel pipe is the same, but the straight seam welded pipe will inevitably have a lot of T-shaped welds, so the probability of welding defects is also greatly improved, and the welding at the T-shaped welded seam is also greatly improved. The residual stress is large, and the weld metal is often in a three-way stress state, which increases the possibility of cracks. Moreover, according to the submerged arc welding process, each weld should have an arc starting point and an arc quenching point, but each straight seam welded pipe cannot meet this premise when welding the circumferential seam, so it may be possible at the arc quenching point. There are more welding defects. Therefore, the spiral welded pipe produced has a good quality assurance to ensure that the produced products will not have defects such as cracks.

Strength characteristics of spiral welded pipe and straight-seam welded pipe

When the 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 resultant stress at the weld is δ=δY(l/4sin2α+cos2α)1/2, where α is the helix angle of the weld of the spiral welded pipe. The helix angle of the spiral welded pipe weld is generally 50-75 degrees, so the synthetic stress at the spiral welded seam is 60-85% of the main stress of the straight seam welded pipe. Under the same working pressure, the wall thickness of the spiral welded pipe with the same diameter can be reduced compared with that of the straight seam welded pipe.

Metallurgical properties of spiral welded pipe and straight-seam welded pipe materials

LSAW pipes are produced from steel plates, while spiral welded pipes are produced from hot-rolled coils. The rolling process of the hot-rolled strip mill has a series of advantages and can obtain the metallurgical process 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 compositions to achieve special strength grades and low-temperature toughness, thereby improving the weldability of the steel. But this system is absent in steel plate production plants. The alloy content (carbon equivalent) of the coil is often lower than that of similar grades of steel, which also improves the weldability of the spiral welded pipe.

It should be noted that, because the rolling direction of the spiral welded pipe is not perpendicular to the axis of the steel pipe (its clipping depends on the helix angle of the steel pipe), the rolling direction of the steel plate of the straight seam steel pipe is perpendicular to the direction of the steel pipe axis, therefore, the spiral crack resistance of welded pipe material is better than that of straight seam steel pipe.

The spiral welded pipe and the straight seam welded pipe are systematically compared in terms of the welding process, metallurgical performance, and strength characteristics, and the differences and main differences between the two are analyzed. Functional and metallurgical properties and processes.