Advantages and disadvantages of welded steel pipe and classification

Advantages and disadvantages of welded steel pipe
Wall light table average wall thickness (steel appearance, steel grade resolution, brightness) can be any length. Therefore, it is economically and aesthetically accurate, using low pressure fluids.


Pipe production process is simple, high production efficiency, low cost, fast implementation. Spiral welding higher than normal length, can reduce the large-diameter steel billet production, you can use different diameter billet to produce the same width of the steel pipe. Then, compared with the length of the straight pipe joints, the welding length to increase by 30 to 100%, and the productivity is low. Therefore, most of the smaller straight pipe straight seam welding, the largest diameter spiral welded pipe up.


Welding steel pipe classification
1, high frequency welded pipe features: good tube shape, uniform thickness, internal and external burrs produced by the welding tools, through proper online calibration, strict control of weld quality nondestructive testing, high degree of automation, low production costs. But the relatively thin wall thickness, the diameter is relatively small, generally not more than 12mm in wall thickness, the diameter is generally not more than 610 mm, especially suitable for the production of steel truss structure.


2, LSAW pipe features: welding under static conditions, high quality weld short welds, the probability of small defects. By expanding the full-length steel pipe well, the dimensions are accurate, the wide range of pipe wall thickness and diameter range, the diameter range 406-mm, wall thickness range 6.0-60mm, high degree of automation, compared to seamless steel pipe, which is to reduce production The cost for the construction, bridges, dams, offshore platforms and other steel bearings and columns, long-span structures and wind tower mast seismic requirements.


3, spiral submerged arc welded pipe is characterized by: spiral weld distribution, long weld, especially in dynamic conditions, the welding, the opportunity to cool and leave the molding point, prone to welding hot cracks. Parallel to the crack direction at an angle of the steel pipe shaft, usually 30-70 °. This point of view is exactly the same as the angle of shear failure, so bending, stretching, compressing and twisting performance are far superior to the welding position of LSAW pipe. Because of the limitation, the influence of Ma'ling seam and fish is beautiful. In addition, during the construction process, the intersecting line weld spiral welded the parent node of the broken spiral weld, a larger welding stress, which greatly weakened the safety components, it should strengthen the spiral welded pipe weld nondestructive testing to ensure the welding quality , Otherwise important occasions do not use steel spiral submerged arc welded pipe.

Advantages of lsaw pipe
It can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure so that the steel structure is dense and the mechanical property is improved. This improvement is mainly reflected in the rolling direction so that the lsaw pipe to some extent is no longer isotropic body; pouring bubbles, cracks and loose formation, but also can be welded under high temperature and pressure.

Defects of lsaw pipe
1, Residual stress caused by uneven cooling. Residual stress is the internal self-balance stress in the absence of external force. The hot-rolled steel in all cross-sections has such residual stress. The larger the general section size, the more residual stress. Although the residual stress is self-balanced, the steel components under the action of external force or have a certain impact, such as deformation, stability, fatigue and other aspects may have an adverse effect;

2, After welding, the non-metallic inclusions in the lsaw pipe are pressed into flakes and stratification, which delaminates the performance of the straight-seam pipe in the thickness direction and may appear when the weld shrinks interlayer tear. The local strain induced by weld shrinkage often reaches several times the yield point strain, much greater than the load induced strain.

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