Hit probability of cylindrical objects dropped on pipelines in offshore operations

Abstract

In offshore oil and gas developments, it is mandatory to have a dropped-objects plan that can be provided to the Bureau of Safety and Environmental Enforcement upon request. Dropped objects from offshore platforms during lifting or any other offshore operations may cause damage to pipelines at seabed. In this paper, an advanced in- house tool, DROBS, is first introduced and applied to calculate the trajectory of dropped cylindrical objects. The Monte Carlo (MC) method is used to simulate the random distribution of landing points. The hit probability on pipelines and the mean radii derived from DROBS are estimated. Further, half-normal distribution (HND) is adopted to estimate the horizontal excursion of the falling point, based on such lateral deviation. Finally, the mean radii derived from DROBS and HND methods are compared with the results using Det Norske Veritas' simplified method. Our results show that such a simplified method may introduce larger errors to the calculation of hit probability and mean radii. Because an accurate estimation of the mean radius is very important to pipeline layout design to lower the risks from dropped objects in offshore operations, we believe that the proposed method in this work is more practical and accurate.