Dropped Objects

Abstract

Abstract Dropped objects have constituted the great majority of potential and actual fatalities in offshore drilling. Major oil and gas operators have reported that the dropped objects account for around 60% of their high potential incidents. Tubular overhead equipment and tubular handling equipment items have accounted for the majority of the dropped object categories. The consequences of dropped object may include but not limited to human fatalities/injuries, offshore asset damage/failure, and environment/reputation and business impact. Offshore dropped object risk assessment encompasses the quantification of the risk caused by accidentally dropped objects on potential targets from topsides to seabed. The assessment involves two parts, which are impact frequency estimation and consequence analysis. Often, a risk matrix is used in mitigation decision, that is, high impact frequency and high consequence events require attention. The potential targets from platform deck to seabed pipelines define three types of dropped objects analysis (DOA): topsides DOA, substructure DOA, and subsea DOA. Topsides DOA involves the risk assessment for platform structural components and equipment, while substructure DOA includes any potential targets from the sea surface to the seabed, such as jacket legs and hull. Subsea DOA is often of concern because of the high consequence, both environmental and economic. For impact frequency estimation, the article presents a practical approach in which a two‐step Monte Carlo simulation is used to estimate the impact likelihood for potential targets such as upper decks, jacket legs, risers, mooring lines, and pipelines on seabed. As for the structural consequence analysis, this article presents both the simplified approaches, such as that found in Det Norske Veritas guidelines and advanced nonlinear finite element analysis, which is believed to remove the conservatism in simplified approaches. The dropped object assessment methodology is supplemented with two case studies: one related to subsea dropped object and the other related to topsides dropped object.