Calibration of Load and Resistance Factors of API RP 2A-LRFD, Second Edition, for Fixed Offshore Platforms

Abstract

Fixed offshore platforms in the Gulf of Mexico (GoM) are traditionally designed following the working stress design (WSD) format, that is, the factor of safety approach. In 1993, the first reliability-based design standard for offshore platforms using the Load and Resistance Factor Design (LRFD) format was published by the American Petroleum Institute (API) called Recommended Practice for Planning, Designing, and Constructing Fixed Offshore Platforms—Load and Resistance Factor Design, which is commonly abbreviated as API RP 2A-LRFD 1st edition. API RP 2A-LRFD 1st edition has had a significant influence in developing the LRFD format of the ISO for fixed offshore structures (i.e., ISO 19902), but it was not commonly used in the United States, and it was withdrawn in 2012 due to a lack of maintenance. The API RP 2A-LRFD format was reintroduced in 2014 as a draft 2nd edition. This study was carried out in the context of the plan to prepare the API RP 2A-LRFD 2nd edition under the effort to align and merge the API and ISO standards as a single global standard. The objectives of this study are to assess the fixed offshore platform component reliability with the accumulated experience in the last several decades, and to evaluate the suitability of the load and resistance factors in API RP 2A-LRFD 1st edition for the 2nd edition of API LRFD given the updated metocean characteristics after Hurricane Katrina in the GoM. The key findings of this study are that the LRFD format with the load and resistance factors from API RP2A-LRFD 1st edition gives slightly higher reliability levels for component checks than the WSD format, but lower reliability level with the updated new metocean criteria comparing to the criteria in the 1980s. A list of recommendations on the load and resistance factors was provided to facilitate the preparation for the API RP2A-LRFD 2nd edition.