Operational integrity of pipelines on mobile seabeds: Using survey data to explore trends of changing pipeline embedment and span evolution

Reliable prediction of as-laid embedment and changes in embedment with time for surface-laid offshore pipelines and cables are important for the assessment of their operational response. This study interprets the field data from three sections of the same pipeline route from ROY inspection surveys that took place from the as-laid condition to around six years after installation. The analysis results indicate significant changes of both span ratio (i.e., the proportion of the length that is in span) and the range of embedment of the grounded sections. These changing trends differ between sections of the same pipeline, and include both growing and reducing proportions of span, as well as no formation of spans. In all cases, the average embedment of the non-spanning sections increases with time, and there is a net increase in the stability of the pipeline under hydrodynamic loading. These observations illustrate the importance of understanding the pipeline, metocean and seabed conditions when making predictions of long-term pipeline performance.