An Update on API RP 2A Section 17 for the Assessment of Existing Platforms

Abstract

During the late 1980's it became evident that an API process was required for assessing the structural integrity of existing jacket platforms in the US OCS. The approach would be different from the design of new platforms and as such required a new section of API RP 2A. The offshore community then established an API working group that developed the assessment approach and released it in the mid 1990's as "API RP 2A, Section 17 - Assessment of Existing Platforms." The background and assumptions of Section 17 are described in a series of 1994 OTC papers. Since then, Section 17 has become the worldwide recognized approach for assessing existing platforms. It has been used many times around the world and particularly in the Gulf of Mexico. In August 2003, the MMS released an NTL requiring Gulf of Mexico platform owners to assess their platforms to Section 17 requirements. This paper provides further background, clarifications and proposed updates to Section 17. The paper is divided into three parts. Part I is a discussion on the background and perspective on why and how Section 17 was originally developed including review of some of the basic premises of the document. Part II is a historical perspective on how Section 17 has been implemented over the past seven years, and how platforms that applied the process have performed, including during Hurricane Lili. Part III presents the planned future of Section 17 and proposed clarifications and updates. Part I: The Development of Section 17 The offshore industry started in the Gulf of Mexico in the late 1940's. Drilling and production grew steadily into the 1960's. In the frontier environment where little was know about the details of wave heights and wave loadings, land based practices were extrapolated with apparent success. Various oil companies and contractors developed staffs and procedures to design, install and operate the necessary facilities. The industry had continued success until the early 1960â??s when Hurricanes Hilda in 1964 and Betsy in 1965 swept through the Gulf of Mexico resulting a considerable damage to and loss of a number of platforms. These were the first large scale ("full population") hurricanes that the industry had experienced and it was evident that some guidance was required for platform design. The First API Recommended Practice Following Hurricane Hilda, a group of industry leaders met to discuss issues related to design practice (13). Discussions of return periods for design wave height were one of the key topics. Considerable variance, from 25 year to 100 year periods, was confirmed along with a wide variety of techniques and data for determining the height for a given return period. Additional topics of key importance identified were steel design and foundation characteristics. More important than the actual topics discussed, was the long term result of the meeting. This group of more than 60 met in November 1964 and held what became the first meeting that eventually led to the issuance of the first design guidance for offshore facilities, the API Recommended Practice for the Planning, Design, and Construction Fixed Offshore Platforms in 1969, a 16 page document (11).

Review on Fixed and Floating Offshore Structures. Part II: Sustainable Design Approaches and Project Management

“…As a result, the designs are carried out using peak loads generated by hurricane wind and waves during the platform design life [129][130][131][132][133][134][135]. In addition, fatigue loads induced by waves over the platform's lifetime, as well as platform motion, are all essential design challenges addressed by standards [136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152]. Strong currents can occasionally impact the platforms, putting the integrity of the entire system at a threat, hence the need for designing offshore structures against harsh weather conditions [153][154][155][156][157].…”

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“…The design, maintenance and assessment of offshore structures must meet the requirements laid down in the Code of Federal Regulations, Title 30, Part 250 (30CFR250). The design requirements for offshore facilities follow the recommendations of the American Petroleum Institute which calls for platforms and floating permanent systems to be designed to withstand a fullpopulation hurricane (Wisch et al, 2004) with a return period of 100 years (API, 1997(API, , 2000. These 100-year criteria correspond to a wind speed of about 150 km/h in 1-h average winds or about 180 km/h in sustained 1-min winds and a maximum wave height of 22 m (Ghonheim & Colby, 2005;Kramek, 2006;Ward et al, 2005).…”

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“…And the design requirements for offshore facilities follow the recommendations of the American Petroleum Institute which calls for platforms and floating permanent systems to be designed to withstand a full-population hurricane [24] with a return period of 100 years [25,26]. These 100-year criteria correspond to a wind speed of about 150 km/h in 1-h average winds or about 180 km/h in sustained 1-min winds and a maximum wave height of 22m [12,27,28].…”