Comparison of straight seam welded steel pipe and spiral seam welded steel pipe
According to tube forming technology, steel can be roughly divided into the following four categories: seamless steel pipe, high frequency welded pipe, LSAW pipe, spiral submerged arc welded pipe. According to the form of weld we can be divided into seamless steel pipe, straight seam steel pipe and spiral pipe. The different forms of the weld seam steel pipe and spiral pipe for our comparison.
1, The production process straight seam welded steel pipe is longitudinally parallel with the pipe. Commonly divided into metric welded steel pipe, thin-walled tubes, transformers, cooling tubing and so on. Longitudinal welded pipe production process is simple, high production efficiency, low cost and rapid development. Spiral steel pipe is a strip of steel as the raw material, often warm extrusion molding, automatic double-wire double-sided submerged arc welding process of spiral welded steel pipe.
The strength of spiral welded pipe is generally higher than the straight seam welded pipe, the pipe can be used to produce larger diameter welded pipe with a narrower blank, but also the same width of the blank tube production of different diameter pipe. During the forming process, the steel plate is deformed uniformly, the residual stress is small, and the surface does not produce scratches. Processed spiral pipe in the diameter and thickness of the size of the specification range has more flexibility, especially in the production of high-grade steel thick-walled pipe, especially small-caliber thick-walled tube with other processes have unmatched advantages to meet the user Spiral pipe specifications more requirements. The use of advanced double-sided submerged arc welding process, can be achieved in the best location of the welding, not prone to wrong edge, welding partial penetration and imperfections and other defects, easy to control the quality of welding. However, compared with the same length of straight pipe, weld length increased by 30 ~ 100%, and the production rate is low.
2, Safety Analysis Straight seam steel pipe is mainly caused by uneven cooling caused by residual stress.Residual stress is the internal self-balance stress without external force, all kinds of hot-rolled sections have such residual stress section, the general steel section The larger the size, the greater the residual stress.Residual stress, although self-balancing, but the performance of steel components in the external force or have some impact, such as the deformation, stability, fatigue and other aspects may have adverse effects After welding, the non-metallic inclusions in the straight seam steel pipe are pressed into flakes and stratification occurs, which delaminates the performance of the straight seam steel pipe in the thickness direction and may appear when the weld shrinks Layer tear. Weld shrinkage induced local strain often reaches several times the yield point strain, strain caused by the load is much larger.Moreover, the longitudinal welded pipe will inevitably have a lot of T-shaped weld, so the existence of welding defects The probability is also greatly increased, and T-shaped welds at the welding residual stress is larger, the weld metal is often in the three-state stress, increasing the possibility of cracks.
Spiral submerged arc welded pipe was spiral distribution, long weld, especially in the dynamic conditions of welding, the weld is too late to leave the molding of the cooling point, prone to welding hot cracks. The direction of cracks and weld parallel, and the steel pipe into an angle, usually between 30-70 °. This angle is exactly consistent with the shear failure angle, so its bending, tensile, compressive and torsional performance is far less than the LSAW pipe, at the same time as a result of welding position constraints, saddle-shaped and fish-shaped weld seam Beautiful. In addition, during the construction process, the intersecting line weld at the spiral welded busbar node splits the helical seam, resulting in greater welding stress, thus greatly weakening the safety performance of the component. Therefore, the nondestructive testing of the spiral welded pipe weld should be strengthened, To ensure the quality of welding, or in the case of important steel structures should not be used spiral submerged arc welded pipe.
3, The scope of LSAW pipe using double-sided submerged arc welding process, welding under static conditions, the weld quality, short weld, the probability of defects is very small. Steel pipe through the full-length expansion, good tube shape, accurate size, steel pipe wall thickness range and diameter range, suitable for construction, bridges, levees, offshore platforms and other steel structure bearing columns, large-span structures and wind and earthquake resistance Pole tower mast structure. Spiral pipe is currently a kind of steel commonly used in industry, construction and other industries. Mainly used in water works, petrochemical industry, chemical industry, power industry, agricultural irrigation, urban construction. In summary, we can see two different forms of weld pipe has its own characteristics, according to different applications have different advantages.
Edit by Mr. Bruce Zhang of KRM/BSW
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