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seamless pipe(smls) vs. erw pipe

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Seamless pipe is a hollow cross section, no seams round, square, rectangular steel. Seamless steel ingot is made of perforated or solid tube capillary tube, and then by hot-rolled, cold-rolled or cold-call is made. Seamless hollow sections, a large number of channels for transporting fluids, steel pipe and solid steel bar, etc. compared to the same torsional strength in bending, lighter, is an economic cross-section steel, widely used in the manufacture of structural parts and mechanical parts, such as piling pipe, automotive drive shafts, bicycle frames and construction using steel scaffolding.

ERW steel pipe: the high-frequency straight seam resistance welding pipes, hot-rolled wide coil as raw material, pre-bent, continuous molding, welding, heat treatment, sizing, straightening, cutting and other processes, and the spiral weld compared with the short high dimensional accuracy, uniform thickness, surface quality, the advantages of higher pressure, but the drawback is to produce only small-diameter thin-walled tube, easy to produce gray leaf spot weld, lack of fusion, groove-like corrosion defects. Currently wider application area is the city gas, crude oil transportation and so on.

Mainly molding process differently. Ordinary steel, such as water pipes, generally through after bending the flat sheet by welding together, you can find a seam in the above; diameter is generally thicker welds, mainly for erw pipe. The general is seamless steel molten state through the annular slit backlog stretched out before treatment processes such as molding, so there is no seam. In performance, especially on the bearing capacity has greatly improved as compared with ordinary steel, so often used in high-voltage devices. Hydraulic equipment such as piping connections. While the ordinary steel welds is the weak link, the weld quality is also affected its overall performance of the main factors.

Diameter tolerance
ERW pipe using cold forming by 0.6% reducing sizing completed, the process temperature is almost constant at room temperature, and thus control the exact diameter range of fluctuation is small, will help eliminate black buckle; rather seamless hot-rolled Forming process, the sizing was completed around 8000C, steel raw materials, components, cooling conditions and the status of the cooling rolls have a greater impact on its outer diameter, and thus difficult to accurately control the diameter and larger range.

Seamless steel pipe used in the outer surface of the billet hot rolling process to eliminate defects can not only after the completion of the finished, polished off defects; For left after piercing spiral track, minus the wall in the process, can only be partially eliminated. ERW steel pipe hot rolled coil as raw material, coil surface quality is ERW pipe surface quality, and ease of hot-rolled coil surface quality control and the quality is higher, therefore ERW steel pipe and seamless steel surface quality is far superior .

Tensile Test
Seamless and ERW pipe tensile performance indicators are in line with API standards, but generally at a maximum intensity seamless, plasticity is lower, comparatively speaking, ERW steel pipe strength index in the best condition, plasticity index higher than the standard 33.3% because the ERW pipe raw material - hot-rolled coil is to rely on the performance of micro-alloying smelting, refining and controlled rolling and controlled cooling and other means to ensure; seamless rely mainly on the means to increase the carbon content, it is difficult to ensure strength, ductility a reasonable match.




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