CFD Analysis of scour prediction around subsea pipelines

Near shore crossings of a pipeline are historically at higher risk than other sections. The Varanus Island rupture on June 8, 2008 off the West Australian coast exemplifies the possibility of pipeline failure close to near shore crossings. Due to a number of reasons, including shallow water depths, significant tidal movement and high wave energy, these areas are often difficult to access using standard survey techniques. Remotely operated vehicles (ROVs) are most often operated from a large surface vessel for this purpose. If the water is too shallow divers or other more labor intensive techniques may be required for inspection. The use of Autonomous Underwater Vehicles (AUVs) has been proven to be a lower-cost survey alternative that can be used in these areas. Regardless of the technique, anomalies that may be flagged as potentially threatening to both the internal and external integrity of the pipeline include spanning, lifting and debris. This paper uses previously collected data from ROV, Intelligent Pigging and Inline Inspection (ILI) of a natural gas pipeline to identify areas that may be susceptible to external anomalies including areas of scour. Computational Fluid Dynamics (CFD) is then used to attain wall shear values on the seafloor, based on a set of user defined inputs, around an area of scour. Incorporating soil mechanics, such as Shields Parameter, and the values of wall shear, it is hypothesized by the authors that it may be possible to predict sediment transfer, and therefore predict scour development and possibly scour propagation.