Mooring Design

MODU Mooring Design and Inspection Practice
Presented by Tom Kwan

David Tein Consulting Engineers, Ltd OFFSHORE AND MARINE TECHNOLOGY

MODU Mooring Environmental Criteria
(1) US – AmericanPetroleum Institute API RP 2P – MODU (1984, 1987)
- Design Environment: 1-year 1-

API RP 2SK – MODU and FPS (1997, 2005)
- Design Environment: 5-year (away from other structures) 510-year (close toother structures) 10- The 1997 Revision was Based on Mooring Code Calibration JIP (1995)

(2) International Standard Organization (ISO

19901-7) 19901- API criteria adopted - Norwegian annex:10-year design environment 10-

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Tension Limits and Safety Factors
Analysis Method Intact Intact Quasi-static Dynamic Tension Limit Equivalent (Percent of MBS) Factor of Safety 50 60 70 80 2.01.67 1.43 1.25

Damaged Quasi-static Damaged Dynamic

Chain for MODU and Permanent Moorings

Typical 3 in MODU Chain

6 in Chain for Permanent Moorings

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Overview of Recent 2SK RevisionRevision Began in 2002 and Completed in 2004 To be Issued in 2005 Major Revisions
MODU and Permanent Mooring - Add Pile and Plate Anchor FOS and Design Guide - Allow Higher Uplift Angle for DragAnchors - Add Clearance Criteria - Revise Mooring Proof Load - Add Mooring Hardware Section - Revise Dynamic Positioning Section - No Change in Environmental Criteria Permanent Mooring - Revise ChainFatigue Design Curves - Add Global Analysis Guidelines - Add Spar VIM Design Guide - Add Discussion on Mooring Strength Reliability - Provide NPD and API Wind Spectrum

Comparison of MODU MooringPractice
Gulf of Mexico
- Evacuate Drilling and Production Facilities - Recent Total Failures: Andrew 2 (1992), Lili 1 (2002), Ivan 4 (2004) - There were also Partial Failures - Primary Cause: OverloadingNorth Sea and Other Areas
Manned Facilities Partial Failures Primary Cause: Overloading, Fatigue, Faulty Components

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DeepStar 4404 (2001) - Mooring Reliability Study for Permanent...