Api Bull 2Int-Ex-2007 (American Petroleum Institute).Pdf

2INT EX fm Interim Guidance for Assessment of Existing Offshore Structures for Hurricane Conditions API BULLETIN 2INT EX MAY 2007 Interim Guidance for Assessment of Existing Offshore Structures for Hu[.]

Interim Guidance for Assessment

of Existing Offshore Structures for Hurricane Conditions

Interim Guidance for Assessment of Existing Offshore Structures for

Hurricane Conditions

Upstream Segment

User’s of this Bulletin should not rely exclusively on the information contained in this ment Sound business, scientific, engineering, and safety judgement should be used inemploying the information contained herein.

docu-API publications may be used by anyone desiring to do so Every effort has been made bythe Institute to assure the accuracy and reliability of the data contained in them; however, theInstitute makes no representation, warranty, or guarantee in connection with this publicationand hereby expressly disclaims any liability or responsibility for loss or damage resultingfrom its use or for the violation of any authorities having jurisdiction with which this publi-cation may conflict

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Services, 1220 L Street, N.W., Washington, D.C 20005.

Copyright © 2007 American Petroleum Institute

This Bulletin is under the jurisdiction of the API Subcommittee on Offshore Structures.Nothing contained in any API publication is to be construed as granting any right, by impli-cation or otherwise, for the manufacture, sale, or use of any method, apparatus, or productcovered by letters patent Neither should anything contained in the publication be construed

as insuring anyone against liability for infringement of letters patent

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Page

1 SCOPE 1

1.1 Preface 1

1.2 Purpose .1

1.3 Background 1

1.4 Applicability .2

1.5 Reference Standards .2

1.6 Use of Existing Assessment Results 2

1.7 Limitations 2

1.8 Organization .2

2 ASSESSMENT INITIATORS 3

2.1 General 3

2.2 Assessment Initiators 3

2.3 Fixed Structure Initiators 4

2.4 Floating Structure Initiators .4

2.5 Site Specific Metocean Conditions 4

3 ASSESSMENT APPROACH FOR FIXED STRUCTURES 4

3.1 Scope 4

3.2 Assessment Conditions 5

3.3 Assessment Process 5

3.4 Acceptance Criteria 6

3.5 Configuration Changes 6

4 ASSESSMENT APPROACH FOR FLOATING STRUCTURES 6

4.1 Scope 6

4.2 Assessment Conditions 6

4.3 Assessment Process 7

4.4 Acceptance Criteria 8

4.5 Configuration Changes 9

4.6 Marine Operations Manual 9

5 GENERAL RECOMMENDATIONS FOR ALL STRUCTURES .9

5.1 Scope 9

5.2 Mitigation .9

5.3 Hurricane Preparedness 10

COMMENTARY 11

Tables 2.1 Assessment Initiators Based upon API Bull 2INT-MET 3

3.1 Assessment Approach for Existing Fixed Structures 5

Interim Guidance for Assessment of Existing Offshore

Structures for Hurricane Conditions

1 Scope

1.1 PREFACE

Hurricane Ivan in 2004 and hurricanes Katrina and Rita in 2005 resulted in considerable damage and destruction to fixedand floating facilities in the Gulf of Mexico (GOM) Several API committees are in the process of revising and updatingstandards to incorporate learnings from these and other recent large intense storms like Opal (1995) as well as otherimprovements to the industry’s understanding of hurricane risk which have occurred over the past 15 years One majorchange is a complete revision to the hurricane conditions presently contained in API RP 2A-WSD, 21st Edition, recogniz-ing the higher level of hazard in certain parts of the GOM Another is the revised understanding of the potential for localwave-in-deck damage While work on standards development continues, in the interim the following documents are beingissued to provide immediate guidance for the design and assessment of offshore Gulf of Mexico fixed and floating facili-ties in hurricane conditions:

• 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 2007

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

1.2 PURPOSE

API Bull 2INT-EX is being issued concurrently with API Bull 2INT-MET to give guidance, at a high level, on how to utilize theupdated hurricane winds, waves, surge and current conditions in API Bull 2INT-MET for the assessment of existing offshorestructures The design of new permanent structures is contained in the companion API Bull 2INT-DG

1.3 BACKGROUND

The hurricane metocean conditions presently contained in the 21st Edition of API RP 2A-WSD have not been updatedsince 1993 Since that time, several major severe storms, most notably Opal (1995), Ivan (2004) and Katrina (2005), haveaffected the Gulf, resulting in increases to local extremes in the areas affected by these storms Most importantly, how-ever, industry’s understanding of hurricane risk has continued to evolve Strong evidence now exists for there being aregional 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 earlyperiod of the database are probably biased low in terms of intensity

API Bull 2INT-MET presents new hurricane conditions for four GOM regions: West, West Central, Central and East, all based onthe 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 inthe 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 pri-marily driven by the high frequency of intense storms experienced by this region, and to a lesser degree the elimination of the lesstrusted (pre-1950) portion of the historical hindcast record Conditions in the other three regions vary slightly from each other, butare 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 forexisting structures, particularly in the Central Region and its adjoining transition regions

2 API B ULLETIN 2INT-EX

1.4 APPLICABILITY

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)

1.5 REFERENCE STANDARDS

This document is intended to explain how to use the content of API Bull 2INT-MET with existing structures designed to theseRecommended Practices (RP) and standards:

API

RP 2A-WSD Planning, Designing and Constructing Fixed Offshore Platforms—Working Stress Design, 21st Edition,

December 2000 through Supplement 3, June 2007

RP 2FPS Recommended Practice for Planning, Designing and Constructing Floating Production Systems, 1st Edition,

March 2001

RP 2RD Design of Risers for Floating Production Systems (FPSs) and Tension-Leg Platforms (TLPs), 1st Edition, June

1998

RP 2SK Design and Analysis of Stationkeeping Systems for Floating Structures, 3rd Edition, October 2005

RP 2T Planning Designing and Constructing Tension Leg Platforms, 2nd Edition, August 1997

Bull 2TD Guidelines for Tie-downs on Offshore Production Facilities for Hurricane Season, 1st Edition, June 2006

These standards, have been actively applied in designs in U.S waters, and include guidance, methods and criteria to apply ocean conditions

met-Nothing in this Bulletin is intended to suggest, recommend or endorse a relaxation of provisions in existing API Standards, which remain in effect The more severe of the metocean conditions in API Bull 2INT-MET or the metocean conditions in existing API Standards should be applied, unless metocean conditions derived from a valid site specific investigation are used.

1.6 USE OF EXISTING ASSESSMENT RESULTS

Specific assessment approaches using structural analyses are described in this document In many cases, results from an existingassessment or structural analysis that was previously performed on the structure or a similar structure can be used in lieu of theassessments described herein In such cases, the previous studies should be representative of the structure’s current configurationand condition

1.7 LIMITATIONS

This Bulletin is applicable for existing offshore structures located in the Gulf of Mexico at the time of the publication of this letin The guidance in this document is not intended for use in designing new platforms For the design of new platforms, see APIBull 2INT-DG

Bul-Platforms designed according to API Bull 2INT-DG should not use this guide for assessment once the structure is installed, unlesssome assessment initiator other than functional expansion occurs

1.8 ORGANIZATION

This Bulletin is organized depending upon whether the structure is fixed or floating and upon its location Section 2 describes theinitiators that are used to determine if a structure should be assessed Once this is determined, Section 3 describes the assessmentapproach for fixed structures and Section 4 describes the assessment approach for floating structures Section 5 provides generalrecommendations that should be applied where appropriate to all offshore structures in the GOM in order to reduce the risks andconsequences of damage from hurricanes

A commentary is included to provide additional guidance and explain the reasons for selecting the values for this Bulletin

I NTERIM G UIDANCE FOR A SSESSMENT OF E XISTING O FFSHORE S TRUCTURES FOR H URRICANE C ONDITIONS 3

A part of this Bulletin shall be considered withdrawn only if:

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 letin superseded

Bul-As for the future, the API Hurricane Evaluation & Bul-Assessment Team (HEAT) is continuing its orderly work on metocean tions, platform robustness/fragility assessment & calibration, learnings on the direct and indirect economic impact of platformfailures, and safety issue mitigations beyond current personnel evacuation, SCSSV, and P&A practices Modifications to theseInterim Guidelines may be expected in terms of practical tradeoffs, evolving practices, and revisions of the referenced standards

condi-2 Assessment Initiators

2.1 GENERAL

An assessment initiator is used to determine if a platform should be assessed for the API Bull 2INT-MET hurricane conditions.The assessment initiator is based upon a structure’s location and if it is fixed or floating The location is important since it deter-mines the specific metocean conditions to be used according to API Bull 2INT-MET

Fixed structures include steel jacket or template platforms, towers and compliant towers, caissons, minimum non-jacket and cial structures that are fixed to the seafloor These structures follow API RP 2A-WSD guidelines

spe-Floating structures include Tension Leg Platforms (TLP), and permanently moored Spars, Deep Draft Caissons, semi bles and any other type of floating or tethered structures These structures follow API RP 2T, API RP 2FPS, and API RP 2SKguidelines

submersi-2.2 ASSESSMENT INITIATORS

The fixed and floating structures that should be assessed are shown in Table 2.1 based upon the hurricane conditions presented inAPI Bull 2INT-MET If an assessment is initiated, then the assessment should be performed according to the assessment approach

as described in the indicated section of this Bulletin

Structures located in the transition regions adjacent to the Central Region should also be assessed In some locations, the updatedmetocean conditions in the transition region may not have increased as defined in API Bull 2INT-MET and in this situation thestructure does not have to be assessed per this Bulletin See the appropriate fixed or floating assessment section of this documentfor additional guidance

If an assessment is not initiated, then a structure should continue to operate according to existing API guidelines relevant for thestructure However, regardless if an assessment is initiated, all fixed and floating structures located anywhere in the GOM shouldconsider the General Recommendations described in Section 5 in order to minimize risks of hurricane damage

Additional discussion of the assessment initiators is described in the remainder of this section

Table 2.1—Assessment Initiators Based upon API Bull 2INT-MET

Structure API Category 1 Location 2 Assessment Initiated Assessment Approach

Fixed

Notes:

1API RP 2A-WSD, 21st Edition, Supplement 2, 2005, provides definitions of API Categories L-1, L-2 and L-3

structures are those that were designed to API RP 2A, 21st Edition

2Regions are defined in API Bull 2INT-MET

4 API B ULLETIN 2INT-EX

2.3 FIXED STRUCTURE INITIATORS

Fixed structures should be assessed according to their API Category defined in API RP 2A-WSD, Section 17 and Section 1 Theassessment should follow the guidance contained in API RP 2A-WSD, Section 17 as modified by the information contained Sec-tion 3 of this Bulletin and should use API Bull 2INT-MET or a valid site specific study for metocean conditions

Existing fixed structures designed prior to API RP 2A-WSD, 21st Edition are categorized according to Assessment Categoriesdefined in API RP 2A-WSD, Section 17 There are three Assessment Categories consisting of A-1 High Assessment Category, A-

2 Medium Assessment Category and A-3 Low Assessment Category The assessment initiators for these platforms are rized as follows:

summa-• A-1 structures located in the Central Region and the associated transition regions should be assessed for the updated ricane conditions A-1 structures located in the other three regions do not need to be assessed for the purposes of thisBulletin

hur-• A-2 structures located anywhere in the four regions do not need to be assessed for the purposes of this Bulletin

• A-3 structures located anywhere in the four regions do not need to be assessed for the purposes of this Bulletin

Existing fixed structures designed according to API RP 2A-WSD, 21st Edition are defined according to Exposure Categoriesdefined in API RP 2A-WSD, Section 1 These structures are categorized as L-1, L-2 and L-3, with the categorization dependingupon life-safety and consequences of failure According to API RP 2A-WSD, 21st Edition, these structures are not intended to usethe assessment approaches and reduced criteria contained in Section 17, and instead, assessment should be in accordance with thecriteria originally used for design of the structure However, for the purposes of this Bulletin, existing L-1 structures located in theCentral Region and located in the adjoining transition regions should be considered as A-1 structures and also follow the assess-ment approach as described in Section 3 The assessment initiators for these platforms are summarized as follows:

• L-1 structures located in the Central Region and located in the adjacent transition regions should be considered an A-1structure for the purposes of this Bulletin L-1 structures located in other three regions do not have to be assessed for thepurposes of this Bulletin

• L-2 and L-3 structures located anywhere in the four regions do not need to be assessed for the purposes of this Bulletin.L-2 structures are designed to a higher level of strength than required for life safety on A-2 manned-evacuated structures There is

no formal recommendation for assessing L-2 structures in the Central Region on account of their economic importance However,the stakeholders may want to assess these structures for purposes of risk evaluation and mitigation, particularly for processing andtransportation hubs See Commentary

2.4 FLOATING STRUCTURE INITIATORS

Floating structures located in the Central Region and located in the adjacent transition regions should be assessed The assessmentshould follow the guidance contained in Section 4 and should use API Bull 2INT-MET or a valid site specific study for metoceanconditions

Floating structures located in the three other regions do not need to be assessed for the purposes of this Bulletin

2.5 SITE SPECIFIC METOCEAN CONDITIONS

This document refers to API Bull 2INT-MET for updated Gulf of Mexico hurricane conditions Alternatively, a valid site specificmetocean study may be used provided that the study is conducted according to the guidance contained in API Bull 2INT-MET

3 Assessment Approach for Fixed Structures

3.1 SCOPE

Fixed structures should be assessed according to their API Category and locations as previously shown in Table 2.1 Table 3.1shows the associated assessment conditions and acceptance criteria The assessment approach generally follows that described inAPI RP 2A-WSD, Section 17, with the exception of the use of metocean conditions per API Bull 2INT-MET Additional guid-ance is provided in the remainder of this section