Spiral steel pipes and straight-seam steel 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 technical characteristics of spiral steel pipe and straight seam steel pipe are as follows:
The first is the difference in the welding process:
In terms of the welding process, the welding method of spiral steel pipe and straight seam steel pipe is the same, but straight seam steel pipe will inevitably have a lot of T-shaped welds, so the probability of welding defects is also greatly increased, and the welding at T-shaped welds The residual stress is 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. There are more welding defects. Therefore, the spiral steel pipes produced have good quality assurance, ensuring that the products produced will not have defects such as cracks.
· Strength characteristics of spiral steel pipe and straight seam steel 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 steel pipe. The helix angle of the spiral steel pipe weld is generally 50-75 degrees, so the synthetic stress at the spiral weld is 60-85% of the principal stress of the straight seam welded steel pipe. Under the same working pressure, the wall thickness of the spiral welded steel pipe with uniform pipe diameter can be reduced compared with the straight seam welded steel pipe.
· Metallurgical properties of spiral welded steel pipe and straight seam welded steel pipe materials:
Longitudinal submerged arc welded pipes are produced with steel plates, while spiral welded steel pipes are produced with hot rolled coils. 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 does not exist in the steel plate production plant. The alloy content (carbon equivalent) of the coil tends to be lower than that of similar grades of steel, which also improves the weldability of spiral steel pipes.
What needs to be explained is that because the rolling direction of the spiral welded steel 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 axis of the steel pipe, therefore, The crack resistance of spiral welded steel pipe material is better than that of straight seam steel pipe.
The spiral welded steel pipe and the straight seam welded steel 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, and the welding process and method of each pipe fitting are introduced in detail. Strength function, and metallurgical function and process.
Post time: Jul-11-2023