In recent years, several natural gas pipeline projects have been planned for permafrost regions. Pipelines laid in such areas are subjected to large plastic deformation as a result of ground movement due to repeated thawing and freezing of the frozen ground. Likewise, in pipeline design methods, research on application of strain-based design as an alternative to the conventional stress-based design method has begun. Much effort has been devoted to the application of strain-based design to high strength linepipe materials. In order to verify the applicability of high-strain X100 linepipe to long distance transmission, a large-scale X100 pipeline was constructed using linepipe with an OD of 42 and wall thickness of 14.3mm. This paper presents the results of experiments and Finite Element Analysis (FEA) focusing on the strain capacity of high-strain X100 linepipes. The critical compressive strain of X100 high-strain linepipes is discussed based on the results of FEA taking into account geometric imperfections. The critical tensile strain for high-strain X100 pipelines is obtained based on a curved wide plate (CWP) tensile test using specimens taken from girth welded joints. Specifically, the effect of external coating treatment on the strain capacity of X100 high-strain linepipe is investigated. The strain capacity of the 42 X100 pipeline is considered by comparing the tensile strain limit obtained from girth weld fracture and critical compressive strain which occurs in local buckling under pure bending deformation.

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