This paper presents the research on the bending strain capacity of 40" X70 Line pipe. Full-scale test of pressurized pipe of specific design factors was conducted to demonstrate the compressive strain limit. The numerical analysis based on laser measurement, reverse engineering and finite element method was also performed to investigate the pipe buckling behavior. The results of full-scale test imply that finite element method can predict buckling strain of bent pipe effectively.
Strain-based design refers to pipeline design methodologies to maintain pipeline safety and integrity under large plastic deformation (often defined as total strain greater than 0.5%) (Mohr, 2003). It encompasses both strain demand (applied strain) and strain capacity (strain limit). There are at least two limit states related to SBD: tensile rupture and compressive buckling, which are always considered as ultimate limit state and service limit state, respectively. The tensile rupture leads to breach of pressure containment or deformation boundary and hence very serious. The compressive buckling does not lead to failure of materials directly, but if a rupture occurs due to the local buckling, the consequence is as same as the tensile rupture. The cases depend on the degree of wrinkling result in buckling. Although slight wrinkling can be tolerated during pipeline service, however, local buckling is considered as a kind of failure of pipelines. For the pipelines through permafrost or seismic areas, it is necessary to demonstrate the strain capacity of pipelines under the bending deformation to keep the integrity of pipeline during laying and service (Suzuki and Endo, 2001). It is also an important part of strain-based design methodology. In general, plastic strain concentration develops when local buckling occurred on pipelines after continuous bending. The buckling strain can be evaluated by the ways of full-scale bending test and Finite Element method.
