Impact damage from dropped anchors poses a great threat to the safety of subsea pipelines. Risk assessment by impact of dropped anchors is import for the protection design of subsea pipelines, which usually involves the estimation of the impact frequency and the corresponding damage degree. Although DNV provides recommended practice for calculation of the impact frequency and impact capacity, there is still lack of method to take account of ship traffic and anchoring information in different areas. In this paper, a risk assessment method on subsea pipelines by dropped anchor is proposed based on information from AIS data. The impact frequency was calculated and the corresponding damage degree was classified. The method proposed in this paper could provide assistance in improving the risk assessment of subsea pipelines.
In the offshore oil and gas production system, subsea pipeline is widely laid on the seafloor for the transportation of oil and gas. With the increase of ship traffic and number of subsea pipelines, pipeline damage caused by third-party interferences is also increasing. It has been reported that 50%~60% (2014) of the rupture accidents of subsea oil and gas pipelines in the world are caused by third-party damage, which mainly includes the impact of falling objects at sea, offshore engineering construction, fishing boat trawling and ship anchoring operations. In recent years, damage from dropped anchors has become one of the main risks to the safety of subsea pipelines.
Brown (1972) studied damage risks of pipelines by impacts of dragging anchors and fishing boards. Chung (1996) studied the response and deformation of free-span pipeline under impact load. Al-Warthan (1993) studied pipeline responses to the impact loading types. Tawekal (2019) studied the maximum equivalent stress and depression depth by impact of anchors using ANSYS software. The DNVGL-RP-F107 (2017) gives methods to calculate the damage degree of subsea pipelines impacted by falling objects, which provides a basis for the risk assessment of subsea pipelines by impacts of dropped anchors. With this method, Ariany (2020) performed risk assessment on subsea pipelines by dropped and dragged anchors.
