REQUIRED LINEPIPE PROPERTIES FOR HIGH STRAIN APPLICATIONS AND POSSIBLE RESOLUTION BY PIPE MANUFACTURING TECHNOLOGY

Application of strain based design to pipelines in arctic or seismic areas has recently been recognized as important. So far, there has been much study performed on tensile strain limit and compressive strain limit. However, the relationship between bending buckling (compressive strain limit) and tensile strain limit has not been discussed. A model using actual stress strain curves suggests that the tensile strain limit increases as Y/T rises under uniaxial tensile stress because a pipe manufacturer usually raises TS instead of lowering YS to achieve low Y/T. Under bending of a pipe with a high D/t, an increase in compressive strain on intrados of a bent pipe at the maximum bending moment (epsilon-cp*) improves the tensile strain limit because the tensile strain limit is controlled by the onset of buckling or epsilon-cp* which is increased by lowering Y/T. On the other hand, under bending of a pipe with a low D/t, the tensile strain limit may not be influenced by improvement of buckling behavior because tensile strain on the extrados is already larger than the tensile limit at epsilon-cp*. Finally, we argue that the balance of major linepipe properties is important. Efforts other than the strict demands for pipe properties are also very important and inevitable to improve the strain capacity of a pipeline.