The differences among ERW, SSAW and LSAW


According to the different pipe-making process, the steel pipe can be divided into seamless steel pipe (SML), which is mainly used as the internal oil collection pipe and small-diameter high-pressure gas transmission pipe. The number of long-distance oil and gas transmission pipelines is very small, and most of the long-distance pipelines are It adopts three kinds of straight seam high-frequency welded pipe (ERW), spiral submerged arc welded pipe (SSAW), and LSAW (LSAW). The following table shows the process characteristics and quality performance comparisons of several types of steel pipes:

Straight seam high-frequency welded pipe (ERW) is divided into two types of induction welding and contact welding according to different welding methods. Hot-rolled wide-gauge steel coil is used as raw material, after pre-bending, continuous forming, welding, heat treatment, sizing, straightening, Cutting and other processes, compared with spiral welded pipe with a short weld, high dimensional accuracy, uniform wall thickness, surface quality, high pressure, but the disadvantage is that only small and medium-diameter thin-walled pipe, the weld is easy to produce gray spots , unfused, pitted corrosion defects. At present, the most widely used areas are urban gas and crude oil product transportation.

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When the spiral submerged arc welded pipe (SSAW) is a coiled steel pipe, its advancing direction has a forming angle (adjustable) with the centerline of the forming pipe, and welding is performed while molding. The welding seam is a spiral line. The advantage is that the same specification steel strip can be produced. A variety of diameters of steel pipe, raw material to adapt to a larger range, the weld can avoid the main stress, the force is better, the disadvantage is that the geometric size is poor, the weld length is longer than the straight seam pipe, easy to produce cracks, pores, Slag inclusion, welding deviation and other welding defects, the tensile stress of the welding stress. The design specifications for general oil and gas transmission pipelines stipulate that spiral submerged arc welded pipe can only be used in Class 3 and Class 4 areas. After the improvement of this process in foreign countries, the raw materials are changed to steel plates, so that the forming and welding are separated. After pre-welding and fine boring, cold expansion after welding, the welding quality is close to the UOE pipe. At present, there is no such technology in China. It is a spiral pipe in China. The direction of plant improvement. The spiral pipe used in the “West-to-East Gas Transmission” is still produced according to the traditional process, except that the pipe end has been expanded. The United States, Japan, and Germany generally deny SSAW and believe that the SSAW should not be used in the mainline; SSAW is used in Canada and Italy, and SSAW is used in small quantities in Russia. They also have very strict supplementary conditions. Due to historical reasons, the majority of domestic trunk lines still use SSAW.

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LSAW (Large-Surface Submerged-Arc Welded Pipe) is produced by using a single medium-thickness plate as a raw material, pressing (rolling) the steel plate into a tube blank in a die or a molding machine, and adopting a double-sided submerged arc welding method to expand the diameter. Its product specification range is wide, the toughness, plasticity, uniformity and compactness of the weld seam are good. It has the advantages of large diameter, thick wall thickness, high pressure resistance, low temperature resistance and strong corrosion resistance. In building high-strength, high-toughness, high-quality long-distance oil and gas pipelines, most of the required steel pipes are large-caliber thick-walled LSAW pipes. According to API standards, LSAW pipe is the only designated type of pipe to be used in large-scale oil and gas transmission pipelines when passing through Class 1 and Class 2 areas such as the alpine zone, submarine, and dense urban population.

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