Research progress and prospect of key technologies for high-strain line pipe steel and pipes

Abstract The development and supporting technologies of high-strain line pipe steel and pipes used for oil and gas pipeline projects in special geological environments (such as earthquake zone, landslide zone, mine goaf and subsidence zone) is one of the international research hotspots, and it is also a major problem that China's major oil and gas pipeline projects have to solve. Focusing on a series of key technical difficulties in the research & development and application of high-strain line pipe steel and pipes, a number of theoretical and technological innovations have been achieved after more than ten years of joint researches. And the main achievements are as follows. First, the method of applying many different parameters (e.g. stress ratio, yield to tensile ratio and uniform elongation (UEL)) to comprehensively characterize and evaluate the deformation behavior of steel pipes is proposed, and a technical index system and standard for the new products of X70HD/X80HD high-strain line pipe steel and pipes are established. Second, a complete set of X70HD/X80HD steel plate manufacturing technology is researched and developed, and the high-strain steel plate with the properties of low yield to tensile ratio, high uniform elongation, high stress ratio and high strength and toughness is worked out. Third, the X70HD/X80HD JCOE and UOE high-strain longitudinal submerged arc welded pipe manufacturing technology is researched and developed, reasonable performance matching between a steel pipe and a welding seam is realized, and the performance deterioration in the process of forming, welding, diameter-expending and thermal coating is solved. Fourth, a full-scale test device of steel pipe internal pressure + bending large deformation is independently developed, and the physical simulation based steel pipe deformation test technology is formed. X70HD/X80HD high-strain line pipe steel and pipes have been applied in the West to East Gas Pipeline, the China–Myanmar Pipeline and other major gas pipeline projects in the large scale, and their application effects are remarkable. To satisfy the new needs of pipeline construction and long-term safe operation under complex geological conditions, some suggestions were put forwarded, such as developing new methods of strain-based pipeline design, and researching and developing or improving the supporting technologies suitable for the higher matching requirements of girth weld, such as welding methods, welding materials, welding processes, and girth weld performance quality and defect control requirements.