Comparison Case Study of Risk Assessment of Dropped Objects on Subsea Pipelines

Det Norske Veritas is a company that gives an available classification guidance, which can provide a systematic methodology to estimate the risk due to dropped objects for the purpose of subsea pipeline projection. Firstly, dropped objects simulator (DROBS), which has been developed based on the motion dynamics of cylindrical objects, can be used to calculate the hit probability within a ring area. These results will be compared with the results from DNV’s simplified methodology. Further, they can also be integrated into DNV’s methodology to calculate the annual failure frequency. It is found that DNV may underestimate the failure frequency if compared with the results from DROBS. Three different shield plans are proposed, with 0–60, 0–80, 0–90 m shielded, respectively, to quantify the differences between both methods. In each shield plan, there will be six cases discussed, three for long/flat-shaped objects and the other three for box/round-shaped objects. Through this comparison case study, it is found that only Shield plan III can meet the design criteria base on the original layout design; however, an optimal layout design with a lower cost is also proposed. Overall, the outcome of this study can help optimize offshore pipeline layout design eventually. DOI: 10.1061/ (ASCE) PS.1949-1204.0000569. © 2021 American Society of Civil Engineers.