A probabilistic screening methodology for use in assessment and requalification of steel, template-type offshore platforms

There are over 7,000 offshore platforms worldwide with more than 3,800 in the Gulf of Mexico. This offshore infrastructure is used by the oil and gas industry to furnish over twenty percent of the world's hydrocarbon requirements. Many of these offshore platforms are called upon for extended service beyond their original design life. This makes the need to assess and requalify these structures a high priority concern.; Detailed nonlinear structural analyses are complex and difficult to perform. The programs developed to help engineers perform such analyses require high degrees of expertise to operate properly, are expensive to purchase and maintain, and require large amounts of manpower and time to complete the analyses. Therefore, detailed structural analyses are not the appropriate first step in the process of assessment and requalification of every offshore platform. Resources are limited and have to be competed for. These facts and the large number of platforms that need to be assessed and requalified highlight the need for a practical methodology for screening large fleets of offshore platforms.; The objective of this research was to develop and verify a simplified analytical method for assessment of structural reliability of template-type offshore platforms subjected to severe storm conditions. Verification of these procedures has been accomplished by comparing the results from the simplified analyses with the results from three dimensional, nonlinear analyses of a variety of template-type platforms, with actual field performance of these platforms during past hurricanes, and with the results from large-scale frame tests.; The methodology developed during this research can be used in the process of screening platform fleets that are being evaluated for extended service. In addition, it can be used to help verify results from complex analytical models that are intended to determine the ultimate limit state lateral loading capacities of platforms. Lastly, the simplified procedure can be applied as a preliminary design tool for design of new platforms.; This research is believed to be of interest to offshore structural engineering community, including regulatory agencies, platform owner/operators, and engineering consulting firms.