API Offshore Standards - Underlying Risk Values and Correlation WIth ISO
Authors: Wisch David J. , Banon Hugh H. , Knoll David Alex 
Published: April 2012

This paper provides an overview of the current efforts of API to provide anoverarching standard within the API Series 2 standards for the design andconstruction of offshore structures which would be similar to ISO 19900. Thepaper provides a historical perspective of the current suite of API standards, discussion of the current practices, current issues in the proposed standard(referred to as API RP 2GEN), and future plans.

Offshore structures are designed according to ISO / API standards. The ISO19901 series lists specific requirements for design, construction and operationof offshore facilities with provisions that are applicable to differentfacility types (fixed, floating, or arctic structures), different materials andthe possible range of operating environments. The structure-dependentrequirements for various types of offshore facilities are listed in ISO19902-19906 and corresponding API series.

The ISO / API standards for offshore structures generally followreliability-based design, i.e. the design procedures have been developed orcalibrated to ensure minimum target reliability levels depending on the lifesafety, environmental and economic consequence of failure. It is important torecognize that ISO / API procedures enforce minimum standards on a wide rangeof assumptions and activities: description of actions, modeling and simulationof action scenarios, structural or global analysis, design rules, modeltesting, workmanship, quality control etc. Hence the modification of one ormore aspects of design standards can disturb the delicate balance in the designand lead to unintended consequences in the target reliabilities.

The main objective of API 2GEN standard is to introduce consistency in terms /definitions / assumptions and high level requirements, with special emphasis onthose that are used in setting design reliability targets in the lower levelISO / API documents. The API committee that is developing API 2GEN isrecommending several new definitions related to exposure levels and ULS / ALSrequirements. The emphasis of the committee recommendations is on conditionsapplicable to the Gulf of Mexico (GOM), e.g. shut-in of the wells andevacuation of personnel ahead of forecasted hurricanes

Background -

Structure of Standards

The history of the API series of offshore structures standards, RecommendedPractices (RPs), Specifications (Specs) and Bulletins began in the 1960's andhas been well documented (1) (2). The first standard was API RP 2A released in1967 focusing on fixed steel jackets and decks. The RP was quite expansive inscope covering steel member design, hydrodynamic loading (wind/wave/current), soils and foundations, fabrication, etc. Starting as a 16 page document, the RPrapidly expanded as the industry matured to well over 200 pages by the early1990s and included additional topics such as inspections, installation, welding, etc. With the relative complete coverage of areas such as metocean, foundations and seismic, other API documents, such as RP 2T (Tension LegPlatforms), 2 FPS (Floating Production Systems), 2 SK (Station Keeping), etc.relied upon and referenced RP 2A for numerous technical provisions and providedonly adjustments for this referenced material to properly address the uniquenature of the specific structural/facility application.