Application of Multibeam Data for the Identification of a Possible Free Span on a Subsea Pipeline

Free span on a subsea pipe is a pipe condition in which the pipe is floating and not supported either by seabed sediment or by a structure. Free span conditions can be seen from marine mapping surveys using underwater acoustic equipment, such as side scan sonar and multibeam echosounder. However, for initial identification, it is enough with high-resolution multibeam data without side scan sonar by mapping the pipeline segments that are likely to have free spans. Geometrically, the free span can be measured accurately because multibeam can generate a digital elevation model. Multibeam data has very accurate geometric values for calculating the length and height of the free span, as well as analyzing the potential for seabed depression or scouring in the vicinity. This study discusses the deepening of multibeam data to identify potential free spans in subsea pipelines by the free span risk classification method. This method can provide an overview of which segments of the subsea pipeline have the most potential for a free span. Then the engineering assessment stage can be carried out by conducting a side scan sonar survey to verify the free span condition. This can improve budget efficiency and survey effectiveness.