Pipelines on an erodible seabed are prone to develop free spans, caused by seabed scour around the pipeline and autonomous seabed evolution (e.g. coastal dynamics or sand wave migration).
Exposure of pipelines leads to risk of damage by fishing gear, dropped or dragging anchors and by environmental forces. Free spans cause a risk of loading due to waves and current possibly resulting in pipeline failure due to maximum stress or fatigue. A long, static free span can suffer both from the exceedance of design stress during a storm and from the build-up of fatigue. On the other hand, if the free span is dynamic, there is a high chance of the pipeline getting re-buried without an unacceptable build-up of fatigue. Information on free span evolution is therefore essential in deciding on pipeline stabilisation strategy.
Standard acceptance criteria for scour induced free spans that assume the free spans are static may lead to unnecessary remediation work being undertaken. Aktis Hydraulics has developed analysis techniques which would allow predicting scour and span evolution in time, which results in reduced amount of offshore intervention work required to maintain the pipeline in an acceptable condition.