Hurricane Ivan is one of several hurricanes that have damaged or destroyed fixed offshore platforms in the Gulf of Mexico in recent years. These events provide a unique opportunity to determine the effectiveness of structural design standards and regulations and develop recommendations for changes, if needed. Specifically, Ivan provided an opportunity to evaluate the API RP 2A (RP 2A) design process for fixed platforms to ensure that it provides for well designed structures.
The first part of this paper describes the general impact of Ivan on fixed platforms in terms of survival, damage or destruction. Specific findings and trends are reported related to global platform performance as well as component performance. The second part describes a quantitative assessment to determine the adequacy of the RP 2A design process. The approach uses a probabilistic based process that compares analytically predicted platform damage and survival to that actually observed during Ivan. The result is a Bias Factor that reflects how well RP 2A predicts platform behavior under hurricane loads. The work was funded by the Minerals Management Service (MMS).
Ivan was one of several hurricanes in the last dozen years that have significantly damaged or destroyed fixed offshore platforms. Prior hurricanes are Andrew in 1992 and Lili in 2002. Katrina and Rita in 2005 also caused significant platform damage and destruction. These types of events provide an opportunity to determine how fixed platforms in the Gulf of Mexico perform in hurricanes on both a qualitative and quantitative basis. The qualitative basis includes a review of the typical types of damage to topsides and jacket, as well as the general trends observed, such as the number and type of platforms with wave-in-deck damage. The quantitative basis involves the comparison of the observed damage with what would have been predicted by RP 2A which is the basis for design of fixed platforms in the Gulf of Mexico. This provides a quantified assessment of the accuracy of RP 2A and if it is adequate for design. This paper describes these assessments for Ivan based upon an in-depth study performed for the MMS focusing on fixed platforms (no caissons) [Energo Engineering, 2006]. These types of assessments have been performed previously for Andrew and Lili [Puskar, et. al., 1994 and 2004]. Recent hurricanes Katrina and Rita in 2005 provide similar opportunities, but have yet to be studied.
Ivan developed off the west coast of Africa in late August 2004. By September 5th it was a hurricane about 1,100 miles east of the southern Windward Islands. The hurricane strengthened running south of the Dominican Republic and passed within about 20 miles of Grand Cayman on the 12th. By the late afternoon on September 15th, Ivan was in the eastcentral Gulf of Mexico approaching the deepwater offshore oil and gas facilities. During this time, the hurricane was a Category 4 storm on the Saffir-Simpson scale, with maximum sustained wind speeds of more than135 mph.