Steel pipes can be seen everywhere in our daily life. It is widely used in heating, water supply, oil and gas and other industrial liquids, which brings great convenience to our life and production. According to the tube forming technology, steel tubes can be roughly divided into the following four categories: seamless steel tubes, high-frequency welded tubes, LSAW tubes, and spiral submerged arc welded tubes. According to the form of the weld we can be divided into seamless steel pipe, ERW steel pipe and spiral steel pipe. We have made a corresponding comparison of ERW steel pipes and spiral steel pipes in terms of different forms of welds.
1, production process
ERW steel pipe is a Spiral steel pipe. Usually divided into metric welded steel pipe, welded thin-walled pipe, transformer cooling oil pipe and so on. The ERW welded pipe has a simple production process, high production efficiency, low cost, and rapid development. Spiral steel pipe is a coiled steel pipe made from strip coils as the raw material, which is often warm extruded and welded by an automatic double wire double-sided submerged arc welding process.
The strength of the spiral welded pipe is generally higher than that of the ERW welded pipe. A narrower blank can be used to produce a larger diameter pipe, and a blank having a different diameter can be produced from a blank of the same width. During the forming process, the steel plate is uniformly deformed, the residual stress is small, and the surface is free of scratches. The processed spiral steel pipe has greater flexibility in the range of diameters and wall thicknesses, especially in the production of high-grade thick-walled pipes, especially small- and medium-caliber thick-walled pipes, which have unparalleled advantages over other technologies and can satisfy users. More requirements on the specifications of spiral steel pipe. The use of advanced double-sided submerged arc welding technology can achieve welding in the best position. It is not prone to defects such as misalignment, welding deviation and incomplete penetration, and it is easy to control the welding quality. However, compared with the ERW pipe of the same length, the length of the weld seam increases by 30 to 100%, and the production speed is low.
2, security analysis
ERW steel pipe is mainly subjected to residual stress caused by inhomogeneous cooling. Residual stress is the stress of internal self-phase equilibrium under no external force. Hot rolled section steel of various sections has such residual stress. The larger the section size of general steel, the residual The stress is also greater. Although the residual stress is self-balanced, it still has certain influence on the performance of steel components under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance; after welding, The non-metallic inclusions inside the ERW steel pipe are pressed into thin slices, and the delamination phenomenon occurs. The delamination weakens the performance of the ERW steel pipe in the thickness direction, and there is a possibility of interlayer tearing when the weld seam shrinks. The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than the strain caused by the load. In addition, the ERW welded pipe will inevitably have many T-welds, so the probability of welding defects is also greatly improved. Moreover, the welding residual stress at the T-weld is large, and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracking.
Spiral submerged arc welded pipe spiral weld distribution, long weld, especially in the dynamic conditions of welding, the weld is too late to leave the molding point of cooling, easy to produce welding hot cracks. The direction of the crack is parallel to the weld and is at a certain angle to the axis of the steel tube, typically between 30-70°. This angle is just in line with the shear failure angle, so its bending, tensile, compressive and torsional resistance is far inferior to the LSAW pipe. At the same time, due to the limitation of the welding position, the resulting saddle shape and ridge-shaped welding seam influence Beautiful. In addition, during the construction process, the intersecting line welds at the spiral welded parent pipe joints split the spiral joints and generate larger welding stress, which greatly weakens the safety performance of the components. Therefore, the non-destructive testing of the spiral welded pipe joints should be strengthened. Ensure welding quality, otherwise spiral submerged arc welded pipe should not be used in important steel structure occasions.
3, the scope of application
LSAW pipe adopts double-side submerged arc welding process. Welding under static conditions, the quality of the weld is high, the weld is short, and the probability of defects is very small. The steel pipe expands through full-length, has a good pipe shape, and is precise in size. The steel pipe has a wide wall thickness range and a wide range of pipe diameters. It is suitable for supporting columns, ultra-large span building structures, such as buildings, bridges, dams, and offshore platforms, as well as wind-resistant and earthquake-resistant structures. Pole mast structure. Spiral steel pipe is a kind of steel commonly used in industry, construction and other industries. Mainly used in tap water projects, petrochemical industry, chemical industry, power industry, agricultural irrigation, urban construction.
In summary, we can see that the two different types of welded seam pipes have their own characteristics and have different advantages according to different applications.