API early in 1926 released by the American Petroleum Institute (API) API-5Lstandard, initially including three steel grade A25, A, B, and later released several times. Prior to 2000, the worldwide use X70, about 40%, X65, X60 are in the 30%, a considerable number of small-caliber product oil pipeline selection of X52 steel grade, mostly for resistance welding straight pipe (ERW steel pipe). China is currently used in the Petroleum Pipeline tube spiral welded pipe (SSAW), LSAW pipe (LSAW), electric resistance welded pipe (ERW). Diameter less than 152mm selection of seamless steel tubes. Of the late 1960s to the 1970s, spiral pipe plant rapid development of crude oil pipelines almost all spiral welded steel pipe, "West-East pipeline region selection spiral welded steel pipe. The spiral welded steel pipe of the disadvantage is the internal stress is large, the dimensional accuracy is poor, the probability of generation of defects. According to expert analysis, should adopt the policy of "walking on two legs", and actively carry out technological transformation now spiral welded pipe plant, also in promising; vigorously develop straight seam submerged arc control tube industry in China. ERW steel pipe with a smooth appearance, high dimensional accuracy, lower prices, and has been widely used at home and abroad. Straight seam high frequency welded steel molding process is with advanced, reliable quality, welding position, stable welding parameters, welding speed, high yield, and the entire production line equipment and technology are world-class level. (1) straight seam high frequency welded steel pipe forming process springback small residual stress. (2) the strain hardening effect is small, precise geometric dimensions full circle, will help ensure the quality of construction and welding. (3) straight seam high frequency welded steel bead shape is good, not prone to biting edge, inside and outside the weld misalignment defects. (4) straight-seam pipe weld distributed in a point on the circumference and, therefore, according to the demand to weld on a favorable position. API 5L welded steel pipe is mainly used for the delivery of the onshore and offshore oil and gas, coal slurry, the slurry media and offshore platforms, power plants, chemical industry and urban construction, structural tubes.
