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Hurricane Ivan in 2004 and hurricanes Katrina and Rita in 2005
resulted in considerable damage and destruction to fixed and
floating facilities in the Gulf of Mexico (GOM). Several API
committees are in the process of revising and updating standards to
incorporate learnings from these and other recent large intense
storms like Opal (1995) as well as other improvements to the
industry's understanding of hurricane risk which have occurred over
the past 15 years. One major change is a complete revision to the
hurricane conditions presently contained in API RP 2A-WSD, 21st
Edition, recognizing the higher level of hazard in certain parts of
the GOM. Another is the revised understanding of the potential for
local wave-in-deck damage. While work on standards development
continues, in the interim the following documents are being issued
to provide immediate guidance for the design and assessment of
offshore Gulf of Mexico fixed and floating facilities in hurricane
• API Bulletin 2INT-MET Interim Guidance on Hurricane
Conditions in the Gulf of Mexico, May 2007.
• API Bulletin 2INT-DG Interim Guidance for Design of
Offshore Structures for Hurricane Conditions, May 2007.
• API Bulletin 2INT-EX Interim Guidance for Assessment of
Existing Offshore Structures for Hurricane Conditions, May
The content of API Bull 2INT-MET is undergoing extensive review
and evaluation. The final results are planned to be included in a
new, stand-alone document (API RP 2MET) that will contain the
metocean conditions for use with other API design standards. API RP
2MET will also serve as the basis for a revised U.S. Regional Annex
in ISO 19901-1.
API Bull 2INT-EX is being issued concurrently with API Bull
2INT-MET to give guidance, at a high level, on how to utilize the
updated hurricane winds, waves, surge and current conditions in API
Bull 2INT-MET for the assessment of existing offshore structures.
The design of new permanent structures is contained in the
companion API Bull 2INT-DG.
The hurricane metocean conditions presently contained in the
21st Edition of API RP 2A-WSD have not been updated since 1993.
Since that time, several major severe storms, most notably Opal
(1995), Ivan (2004) and Katrina (2005), have affected the Gulf,
resulting in increases to local extremes in the areas affected by
these storms. Most importantly, however, industry's understanding
of hurricane risk has continued to evolve. Strong evidence now
exists for there being a regional dependence for large, intense
wave-making storms. Also, investigations into the underlying
hurricane record, HURDAT, used as the foundation for the industry's
storm hindcast database, have revealed that storms from the early
period of the database are probably biased low in terms of
API Bull 2INT-MET presents new hurricane conditions for four GOM
regions: West, West Central, Central and East, all based on the
1950 through 2005 period of the industry's hindcast database.
Differences from hurricane conditions in API RP 2A-WSD, 21st
Edition are most pronounced in the Central region; the updated
deepwater 100-year return period significant wave height in the
Central region is 15.8 m (52 ft), in contrast with the 12 m (40 ft)
value implied by API RP 2A-WSD. The differences are primarily
driven by the high frequency of intense storms experienced by this
region, and to a lesser degree the elimination of the less trusted
(pre-1950) portion of the historical hindcast record. Conditions in
the other three regions vary slightly from each other, but are
close to the values in API RP 2A-WSD.
The main objective of this Bulletin is to provide updated
guidance for the use of hurricane metocean conditions in the GOM
for existing structures, particularly in the Central Region and its
adjoining transition regions.
This document is intended to cover the design of the structural
systems of the following types of offshore structures:
1. Steel template platforms and compliant towers.
2. Minimum non-jacketed and special structures (including
caissons) defined in API RP 2A-WSD.
3. Tension Leg Platforms (TLPs).
4. Moored, floating platforms (semi-submersible shaped, spar
shaped, ship shaped).
USE OF EXISTING ASSESSMENT RESULTS
Specific assessment approaches using structural analyses are
described in this document. In many cases, results from an existing
assessment or structural analysis that was previously performed on
the structure or a similar structure can be used in lieu of the
assessments described herein. In such cases, the previous studies
should be representative of the structure's current configuration
This Bulletin is applicable for existing offshore structures
located in the Gulf of Mexico at the time of the publication of
this Bulletin. The guidance in this document is not intended for
use in designing new platforms. For the design of new platforms,
see API Bull 2INT-DG.
Platforms designed according to API Bull 2INT-DG should not use
this guide for assessment once the structure is installed, unless
some assessment initiator other than functional expansion
This Bulletin is organized depending upon whether the structure
is fixed or floating and upon its location. Section 2 describes the
initiators that are used to determine if a structure should be
assessed. Once this is determined, Section 3 describes the
assessment approach for fixed structures and Section 4 describes
the assessment approach for floating structures. Section 5 provides
general recommendations that should be applied where appropriate to
all offshore structures in the GOM in order to reduce the risks and
consequences of damage from hurricanes.
A commentary is included to provide additional guidance and
explain the reasons for selecting the values for this Bulletin.
A part of this Bulletin shall be considered withdrawn only
1. The Bulletin is withdrawn in its entirety, or
2. A standard listed in 1.5 is revised, and the new edition
contains a specific statement declaring the relevant part of this
As for the future, the API Hurricane Evaluation & Assessment
Team (HEAT) is continuing its orderly work on metocean conditions,
platform robustness/fragility assessment & calibration,
learnings on the direct and indirect economic impact of platform
failures, and safety issue mitigations beyond current personnel
evacuation, SCSSV, and P&A practices. Modifications to these
Interim Guidelines may be expected in terms of practical tradeoffs,
evolving practices, and revisions of the referenced standards.
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