Hurricane Lili's Impact on Fixed Platforms and Calibration of Platform Performance to API RP 2A

Abstract

Abstract When Hurricane Lili passed through a region of offshore platforms in September 2003, it provided a new opportunity to 'test' the API RP 2A design process for fixed base platforms to ensure that it provides for well designed structures. While most platforms survived Lili, some were damaged and some failed. It takes all three of these results to adequately test a design code. The last similar opportunity was Hurricane Andrew in 1992. At that time, a Joint Industry Project (JIP) was initiated that developed such a testing process and demonstrated that API RP 2A was indeed functioning adequately, and results in a predictable platform design. The JIP was also used to assist in development of API RP 2A Section 17. The first part of this paper describes the general impact of Hurricane Lili on offshore fixed platforms in terms of survival, damage and collapse of platforms. Specific findings and trends are reported related to global platform performance as well as component performance. The second part of the paper discusses an update to the Andrew JIP using results of several detailed platform assessments from Hurricane Lili. The approach uses a probabilistic "Bayesian" updating process to determine the adequacy of the API RP 2A platform structure design process, based upon "observed" platform failures and survivals during Lili. The result is a bias factor that reflects how well API RP 2A predicts platform behavior under extreme loads. The work was funded by the Minerals Management Service (MMS). Background In 1992, Hurricane Andrew damaged numerous offshore platforms in the Gulf of Mexico, causing several to collapse. This presented a unique opportunity to "test" the API RP 2A design process by comparing platforms that survived, were damaged, or failed in hurricane Andrew against what API RP 2A would have predicted. A Joint Industry Project (JIP) was initiated that developed and implemented a probabilistic comparison process based upon Bayesian updating. The process indicated that the API RP 2A design approach results in a conservative platform design with about 10 to 20 percent margin -- prior to the application of factors of safety. With the normal factors of safety included, the conservatism would be much higher. The Andrew JIP was funded by over 20 organizations including the MMS. There were two phases of the JIP as described in references 1 to 3. Hurricane Andrew provided a unique opportunity for such a comparison process. However, one of the limiting factors was that only 13 platforms were used in the comparison process. Also, many of the platforms were in the same vicinity (South Timbalier), and of similar design (old Gulf Oil). Also at that time, API was in the process of developing API RP 2A Section 17, which establishes a procedure for the assessment of existing platforms. The Andrew JIP was used by the API Section 17 Task Group to help test and calibrate the Section 17 process for assessment of existing platforms. In 2002, Hurricane Lilly damaged several platforms, including a few that were a complete loss.