Development of API RP2 Met: The New Path for Metocean
Authors: Stear James B. 
Published: October 2008

Building on the work of the API HEAT initiative, a stand-alone API recommended practice on metocean conditions is in development. This document, tentatively designated "RP 2MET," is closely aligned with the ISO metocean standard 19901-1. The document contains extensive guidelines on hurricane conditions in the Gulf of Mexico, as well as guidelines on other phenomena like winter storms, the Loop Current, and other deep water current mechanisms, all developed with the latest industry understanding. The development of this document represents a new chapter in API offshore standards, as, following the ISO pattern, metocean conditions have been broken out from their traditional location in RP 2A and expanded beyond focus on those conditions which govern the design of fixed shallow water platforms, and are now available for easy reference by all other RP's.

Introduction

When the API Hurricane Evaluation and Assessment Team (HEAT) undertook steps in 2006 to update the hurricane metocean conditions published in the 21st edition of API RP 2A (1), 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, 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 (2), 2FPS (3) and 2SK (4). 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: the proposed RP 2MET.

In keeping with the " align and merge?? strategy being followed to reconcile API and ISO standards, the new RP 2MET document in development is essentially a copy of the existing ISO 19901-1 " Petroleum and Natural Gas Industries - Specific Requirements for Offshore Structures - Part 1: Metocean Design and Operating Considerations?? (5). Key changes and updates are being made to various sections, with the majority being in the Annex C.4 covering the Gulf of Mexico. As a step towards the publication of the stand-alone RP on metocean conditions, API published Bulletin 2INT-MET in May 2007 (6), which contains updated hurricane conditions previously developed by the API metocean resource group and documented in Berek et al. (7). The resource group anticipates being able to issue the draft 1st edition RP 2MET, which will include the material previously published in 2INT-MET, by the end of 1st quarter 2008.

This paper reviews the layout of the draft metocean document, highlighting alignment between material previously published in RP 2A, and also reviews the upkeep strategy for the document.