Impact against empty and water-filled X65 steel pipes - Experiments and simulations

Offshore pipelines are frequently subjected to accidental impact loads, e.g. from anchors or trawl gear. A lot of parameters - including the pipe geometry, material properties, pipeline content, impact velocity, etc. - influence the course of such an impact. Some of these parameters have been studied quite extensively while others not so much. This study presents material and component tests on specimens taken from an X65 offshore pipeline. Empty pipes, as well as open and closed water-filled pipes, are impacted at different velocities. Results in terms of force-displacement curves are quite similar for the empty and open water-filled pipes, while the closed water-filled pipes react differently as a consequence of internal pressure build-up during impact. Computer simulations of the component tests are carried out using various numerical techniques for fluid discretisation and for fluid-structure interaction. Numerical results are generally in good agreement with experimental observations and serve as a helpful aid when interpreting results.