Calibration of a constitutive material model for sub-sea pipelines

The bulk transport of oil and gas are today carried out by pipelines, and the maximum economical and feasible transport distance and installation environment is constantly extended. This has challenged the need for advanced technology for the whole life cycle of pipelines. New design challenges have to be dealt with concerning arctic environmental loads, but also accidental loads such as anchoring, dropped objects, fishing activities, vessel impact, and of course ice gouging. Thus, considering the actual and increasingly high demands for energy and the challenges with respect to inspection, monitoring and repairing, reliable design criteria are fundamental. Here, numerical simulations are important tools, but the reliability of such simulations of pipelines subjected to different load scenarios rely on a proper modelling of the pipe material. Hence, the aim of this paper is the calibration of a suitable constitutive model for a typical material used in a sub-sea pipeline. Starting from a large experimental test matrix, executed on specimens cut directly from a pipe, the calibration of a material model with an anisotropic yield function and a ductile failure criterion is presented in some detail. In particular the choice of a suitable yield surface to take into account the strong anisotropic flow properties found in the experimental tests is underlined.