Spiral welded and straight seam welded pipes have different technical characteristics and production processes. They have many differences and distinctions in production, have different functions and uses, and have different values in use. The technical characteristics comparison of spiral welded pipe and straight seam welded pipe are as follows:
1. The first is the difference in the welding process:
In terms of the welding process, the welding methods of spiral welded pipes and straight seam steel pipes are the same. Still, straight seam welded pipes will inevitably have many T-shaped welds, so the probability of welding defects is also greatly increased. The welding at the T-shaped welds. The residual stress is large and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracks. Moreover, according to the process regulations of submerged arc welding, each weld should have an arc starting point and an arc extinguishing point. However, each straight seam welded pipe cannot meet this condition when welding the circumferential seam, so there may be arc extinguishing points. 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.
2. Strength characteristics of spiral welded pipe and straight seam welded pipe:
When a pipe is subjected to internal pressure, it usually produces two main stresses 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 spiral welded pipe weld. The helix angle of the spiral welded 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 pipe. Under the same working pressure, the wall thickness of spiral welded pipes with the same diameter can be reduced compared with straight seam welded pipes.
3. Metallurgical properties of spiral welded pipe and straight seam welded pipe materials:
Longitudinal submerged arc welded pipes are produced from steel plates, while spiral welded pipes are produced from hot rolled coils. The rolling process of a hot strip mill has a series of advantages and has the metallurgical process capability to produce high-quality pipeline steel. For example, installing a water cooling system on the output stage to accelerate cooling allows the use of low alloy compositions to achieve special strength grades and low-temperature toughness, thereby improving the weldability of the steel. However, this system is not available in steel plate manufacturing plants. The alloy content (carbon equivalent) of coiled plates is often lower than similar grades of steel plates, which also improves the weldability of spiral welded pipes.
What needs more explanation is that because the rolling direction of the spiral welded pipe is not perpendicular to the axis of the steel pipe (its clamping depends on the spiral angle of the steel pipe), while the rolling direction of the steel plate of the straight seam steel pipe is perpendicular to the axis of the steel pipe, therefore, the spiral The crack resistance of welded pipe materials is better than that of straight seam steel pipes. This paper systematically compares spiral welded pipes and straight seam welded pipes in terms of welding process, metallurgical properties, and strength characteristics. It focuses on analyzing the differences and main differences between the two. It also introduces in detail the welding process and method of each pipe fitting and the strength. Functional and metallurgical functions and processes.
Post time: Jan-05-2024