Wave induced fatigue assessment on free spanning pipelines

Abstract

It is well known that geophysical and geotechnical surveys must be performed in a pipeline route to avoid free spans, since this configuration could bring the structural integrity to jeopardy concerning the fatigue behavior, associated with both vortex induced vibration (VIV) or direct waves actions. However, free spans can be formed during the operation phase due to scour or liquefaction processes. With the recent world’s climate changes, phenomena such as hurricanes and extreme storms are becoming more frequent, raising the awareness of the threat from wave loads on offshore structures, such as pipelines. In this work, a three-dimensional numerical model, based on the finite element method (FEM), is developed, with ABAQUS, comprising a pipe modeled with shell elements and a seabed represented by solid elements, and taking into consideration the contact between these two parts. Finally, the work gathers and presents information of 96 analysis, displaying a parametric study that varies the span length, the diameter, the sea state and soil, that is useful to find the sensitivity of each parameter. This thesis applies the results given by the FEM model to evaluate the accumulated fatigue damage in free spanning pipelines due to the action of direct waves, within intermediate waters, considering and briefly commenting some of DNV’s recommended design practices available for this case.