Understanding Structural Analysis Paperback – Import, 1 May 2005by David M. Brohn 

The Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEMRE) contracted DNV to perform a state-of-the-art comparison of API, ISO, and NORSOK existing offshore structural standards. The comparison identifies the differences and attempts to explore the reasons and if possible recommends areas of improvement with application to the US Gulf of Mexico and the West Coast offshore areas. The study showed that even though there may be significant differences in the adopted design approach being Working Stress Design (WSD) or Load and Resistance Factor Design/Limit State Design (LRFD/LSD) and the regional design criteria, the formulations for calculating member and joint or plate/shell stresses are similar in all three standards. It is recommended that further efforts be directed towards the harmonization of the standards. A significant step has been the recent collaboration between API and ISO and to a certain degree NORSOK to adopt a common approach to the development of future offshore structural standards, It appears that the LRFD/LSD methodology will eventually prevail and be applied to future GOM and West Coast offshore fixed and floating structures as it had for Atlantic and Arctic regions. The limited case studies performed using a GOM fixed platform and a spar deepwater floating structure indicate that design environmental criteria are based on similar reliability analyses and definition of probability of failure. Jacket member utilization comparison indicates that both ISO and NORSOK give significantly more conservative formulation for members with cone transitions compared to API. Member and joint utilizations were noted to vary by up to 53% for members and 29% for joints. No one standard was found to be always more conservative than the other two. A single GOM spar case study showed that the ISO/NORSOK LRFD approach gives yield and buckling utilizations that are within about ±10%. Further investigations are recommended for more in-depth evaluation to reach more general conclusions.DET NORSKE

VERITAS BOEMRE TA&R NO. 677 FINAL REPORT ON COMPARISON OF API, ISO, AND NORSOK OFFSHORE

STRUCTURAL STANDARDS DNV Reg. No.: EP034373-2011-01 Revision No.: 1 Date 2012-01-12 Page 2

1 INTRODUCTION 1.1 Background As stated in the Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEMRE) Contract No. M10PC00108 documentation and the DNV proposal No 1-2Q1N5T-01, the objective of this work presented herein is to perform a state-of-the-art review of existing API, NORSOK, and ISO offshore structural standards. The comparison identifies the differences and makes recommendations for their possible resolution with application to the US Gulf of Mexico and the West Coast offshore areas. The main scope of work entails the following ten tasks: 1. Environmental Loads 2. Loading Conditions 3. Structural Steel Design 4. Connections 5. Fatigue 6. Foundation Design 7. In-service Inspection and Maintenance 8. Assessment of Existing Platforms and Floaters 9. Fire, Blast and Accidental Loadings 10. Installation and Temporary Conditions

The approach employed in the study was described in DNV proposal No 1-2Q1N5T-01 and is summarized below for completeness sake. 1.2 Objective The objective of the work is to perform a state-of-the-art review of existing API, NORSOK, and ISO offshore structural standards with respect to structural integrity aspects and produce a comparison report identifying differences and recommendations for their possible resolution for application in US Gulf of Mexico and the West Coast. 1.3 Codes and Standards Table 1-1 lists all documents reviewed as part of this study. Only current revisions in use were considered even though many of these recommended practices (RP’s) and standards are currently under review and may be re-issued in the near future. These standards are also included as references in Section 13.DET NORSKE VERITAS BOEMRE TA&R NO. 677 FINAL REPORT ON COMPARISON OF API, ISO, AND NORSOK OFFSHORE STRUCTURAL

STANDARDS DNV Reg. No.: EP034373-2011-01 Revision No.: 1 Date 2012-01-12 Page 3 Table 1-1: Main Design Codes Number

Revision Title

API RP 2A (WSD) 21st Edition October 2007 Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms – Working Stress Design

API RP 2T 3rd Edition July 2010 Planning, Designing, and Construction Tension Leg Platforms

API RP 2FPS 1st Edition March 2001

Recommended Practice for Planning, Designing, and Constructing Floating Production Systems

API RP 2A (LRFD) 1st Edition May 2003

Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms – Load and Resistance Factor Design

API Bulletin 2INT-MET May 2007 Interim Guidance on Hurricane

Conditions in the Gulf of Mexico

API Bulletin 2INT-DG May 2007 Interim Guidance for Design of Offshore Structures for Hurricane Conditions

API Bulletin 2INT-EX May 2007 Interim Guidance for Assessment of Existing Offshore Structures for Hurricane conditions

ISO 19901-2 1st Edition November 2004 Specific requirements for offshore structures – Part 2: Seismic Design Procedures and Criteria

ISO 19901-6 1st Edition December 2009

Specific requirements for offshore structures – Part 6: Marine Operations

ISO 19902 1st Edition December 2007 Fixed Steel Offshore Structures ISO 19904-1 1st Edition November 2006 Floating offshore structures –

Part 1: Monohulls, Semi-submersibles and Spars

NORSOK Standard N-001 7th Edition June 2010

Integrity of Offshore Structures

NORSOK Standard N-003 2nd Edition September 2007 Action and Action Effects NORSOK Standard N-004 2nd Edition October 2004 Design of Steel Structures NORSOK Standard N-006 1st Edition

March 2009 Assessment of Structure Integrity for Existing Offshore Load-bearing Structures