Coppard, C and Forrest, A and Leong, ZQ and Hargrave, A, Assessment of subsea pipelines, Australasian Corrosion Association. Annual Conference Proceedings 2014, 21-24 September 2014, Darwin, Australia, pp. 546-555. ISSN 1442-0139 (2014) [Refereed Conference Paper]
Integrity of assets is an essential component in the management and maintenance of aging infrastructure the world over. The marine environment is particularly harsh and a major failure, especially in the oil and gas industry, can be devastating for both the environment and the local economy. Pipelines are used around the globe for the transportation of oil and gas, from offshore installations to onshore plants and on to the consumer or industry. 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, which may in turn lead to internal defects. These points include areas of scour resulting in spanning exceeding allowable lengths, possible external concrete coating degradation, and possible loss or displacement of sacrificial galvanic anodes that directly protects the pipeline from corrosion. This data, together with AUV survey data to be collected in 2014, will be used to ascertain the condition of the Tasmanian Gas Pipeline, both internally and externally in near shore crossings. The survey results will also aid the ongoing, and crucial, monitoring of pipeline and be used for temporal validation of a Computational Fluid Dynamics (CFD) model that can be 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. Understanding these processes is essential for the long-term integrity of the pipeline and will add to the management control of pipeline assets.