SS: New API Codes: Updates, New Suite of Standards / "RP 2MET: An API Standard for Metocean"
Authors: Stear James 
Published: July 2010

This paper describes the first edition of RP 2MET, a new API recommended practice applicable to the development of metocean design and operating conditions. The document is aligned with ISO 19901-1, and is available for reference by a parallel set of new API recommended practices for offshore structures, also aligned with their ISO counterparts. The majority of the changes to the core ISO 19901-1 document are in the regional annexes, particularly the annex devoted to the US waters of the Gulf of Mexico. Sections providing guidance on the derivation of Gulf of Mexico site-specific metocean criteria have been added. Indicative hurricane conditions previously published in API RP 2A and API Bulletin 2-INT-MET have been further updated, and information on winter storms, Loop Current eddies and other deepwater Gulf of Mexico phenomena such as Topographic Rossby Waves (TRW) along the Sigsbee Escarpment is also provided. While no update has been made to the US California waters section of the ISO document, a separate annex section with RP 2A legacy example metocean conditions for other US waters such as the East Coast, northern West Coast and the offshore areas of Alaska, has been provided. Other regional annexes from the ISO document are preserved unchanged. In development by the API Metocean Resource Group (RG1) for the past two years, RP 2MET will be issued for final ballot by the members of the API Subcommittee on Offshore Structures (SC 2) in March 2010, and is expected to be available as an API publication in summer 2010.

Introduction

When the API Hurricane Evaluation and Assessment Team (HEAT) undertook steps following the 2004-2005 hurricane seasons to update the hurricane metocean conditions published in the original 21st edition of API RP 2A (2000), it was decided by the API Subcommittee on Offshore Structures (SC2) that the new conditions should be published as part of a stand-alone document addressing only metocean conditions, maintained by a dedicated industry resource group, designated RG1 Metocean, which could in turn be referenced by all other API recommended practices addressing offshore development. This decision was made in recognition that the offshore industry had changed substantially since the last time (1993) published metocean conditions were updated in API RP 2A. In particular, the emphasis of design in the Gulf of Mexico is no longer on fixed platforms in relatively shallow water, the governing design condition for which is typically represented by the 50- or 100-year Hmax with associated wind and current. In the present era of offshore development, additional guidance on the environment needs to be provided for deepwater platforms and floating MODUs, which are covered by different API recommended practices like 2T (2007), 2FPS (2001) and 2SK (2005). In addition to hurricane wind and wave conditions, these facilities and their risers must withstand hurricane inertial currents, currents from Loop/eddy currents, and currents from topographic Rossby Waves (TRWs), detailed guidance on which has not previously been supplied in the RP 2 family. As opposed to having the environment guidance scattered across many recommended practices governing the design of different facility types, the guidance will be provided in one document for common reference by the others, entitled RP 2MET, " Derivation of Metocean Design and Operating Conditions??.