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

Spiral welded pipes and straight seam welded pipes have different technical characteristics and production processes. They have many differences and differences in production, have different functions and uses, and their values in use are also different.

The first is the difference in the welding process: from the welding process, the welding method of the spiral welded pipe and the 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 increased. Moreover, the welding residual stress at the T-shaped weld is relatively large, and the weld metal is often in a three-dimensional 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 extinguishing point, but each straight seam welded pipe cannot meet this premise when welding the circular seam, so the arc extinguishing point may There are more welding defects. Therefore, the spiral welded pipes produced have good quality assurance, ensuring that the products produced 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 composite stress at the spiral weld is 60-85% of the principal stress of the straight seam welded pipe. Under the same working pressure, the wall thickness of spiral welded pipe with uniform pipe diameter can be reduced compared with that of straight seam welded pipe.

Metallurgical properties of spiral welded pipe and straight seam welded pipe materials: straight seam submerged arc welded pipe is produced with steel plate, while the spiral welded pipe is produced with the hot rolled coil. The rolling process of the hot-rolled strip mill has a series of advantages, and it has the metallurgical process ability to produce high-quality pipeline steel. For example, a water cooling system is installed on the output gantry to accelerate the cooling, which allows the use of low alloy composition to achieve special strength grades and low-temperature toughness, thereby improving the weldability of the steel. But this system basically does not exist in the steel plate production plant. The alloy content (carbon equivalent) of the coiled plates is often lower than that of similar-grade steel plates, which also improves the weldability of spiral welded pipe. What needs to be explained is that because the rolling direction of the spiral welded pipe is not perpendicular to the axis of the steel pipe (the clamping solution depends on the helix angle of the steel pipe), and the rolling direction of the steel plate of the straight seam steel pipe is perpendicular to the direction of the axis of the steel pipe. Therefore, the spiral crack resistance of welded pipe materials is better than that of straight seam steel pipes.

The spiral welded pipe and the straight seam welded pipe are systematically compared in terms of the welding process, metallurgical function, and strength characteristics, and the differences and main differences between the two are mainly analyzed. Functions and metallurgical functions and processes.