Consequence-Based Criteria for the Gulf of Mexico: Philosophy & Results
Authors: Ward Emmett G. , Lee Griff C. , Botelho Dirceu L. , Turner J. Ward , Dyhrkopp Felix G. , Hall Rudolph A. 
Published: October 2008

An API Task Group has recently developed Consequence-Based Criteria for the design of new platforms in water depths to 400 feet in the Gulf of Mexico. These criteria recognize that design criteria for a specific platform should reflect the risks appropriate for that platform. Risks considered included both life safety and various consequences of failure including environment, economic loss, public concern. Risks were categorized in three levels, and appropriate criteria were developed for each of these three levels. This paper discusses the philosophy and assumptions incorporated in these new Gulf of Mexico design criteria.

Introduction

The 20th Edition of API RP2A [1] was published in 1993. The design load methodology included in that RP represents the culmination of decades of experience and research, and represents the best technology available for describing design loads on platforms for specified oceanographic design criteria. Wave directionality and currents were explicitly introduced into the design load computation, and specific oceanographic design criteria recommendations for the Gulf of Mexico result in the 100-year return period force levels. However, some claimed the 20th Edition designs would be significantly heavier than those produced using the 9th through 19th Edition designs. And as the 9th through 19th Edition designs had performed satisfactorily, many questioned "why the need for heavier and more expensive platforms"?

The 9th -19th edition designs covered an era from the late 1970s to the early 1990s that represented modern designs that performed well in Hurricane Andrew. Considerable study had been made of this class of platforms prior to the publication of the 20th Edition of API RP2A, Supplement 1 [2], which was published in 1996. Section 17 of that document introduced consequence-based criteria for assessment of existing platforms. As a result, many also questioned "why not consider consequence-based criteria for the design of new platforms?"

Recent economic pressures on new developments have also led to questions like "must all platforms regardless of intended usage be designed to the same criteria"? Also, "can the industry save costs and increase the profitability of marginal projects through the use of consequence-based criteria"?

The API formed a Task Group on Consequence-Based Criteria in 1994 to consider the questions and develop recommendations for consequence-based design criteria for new platforms in the Gulf of Mexico. The recommendations developed by the Task Group are being balloted by the API membership for inclusion in the proposed 21st Edition as of the writing. This paper discusses the philosophy and assumptions incorporated in this new Gulf of Mexico design criteria. A companion paper, OTC 11886 [3], discusses the development and calibration.

Risks Considered for Gulf of Mexico Design Criteria.

Two classes of risks were separately considered - those associated with Life Safety and those associated with Consequences of Failure. Risks involving environmental damage, economic loss, and public concern were included as Consequences of Failure risks. Three levels of risk were defined for each type of risk as indicated in Table 1.