Assessing the behaviour of subsea pipes under impact

Subsea steel pipes are often used to form extensive networks for transporting oil and gas over large distances. Such pipes can potentially be subjected to actions characterized by high loading rates and intensities stemming from accidental loads, due to high-mass low-velocity impacts. In order to ensure that such networks can continue to operate even after being subjected to such extreme loading conditions, it is essential that the behavior of the pipes is characterized by a certain level of resilience. The present study aims to investigate numerically, via dynamic nonlinear finite element analysis, the effect of various parameters on the dynamic response exhibited by pipes under impact loading. The considered parameters are associated with the impacting object, the geometry and the support conditions of the pipes, the level of axial loading as well as the internal and the external pressures imposed onto the walls of the pipes. The numerical predictions, which are validated against relevant published test data, reveal that the above parameters, which are associated with the in-situ conditions imposed onto subsea pipes throughout their operational life, can significantly affect, often detrimentally, the behavior exhibited under impact loading. Existing assessment methods employed in practice for predicting the level of damage sustained by pipes during impact do not accurately consider the effect of the above parameters. As a result, questions are raised concerning the ability of such guidelines to realistically predict the level of damage sustained by subsea pipes under impact.