Design, Manufacture, Installation, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring

API RECOMMENDED PRACTICE 2SM SECOND EDITION, JULY 2014

REAFFIRMED, SEPTEMBER 2020

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Copyright © 2014 American Petroleum Institute

Foreword

API 2SM is under the jurisdiction of the API Subcommittee on Offshore Structures. The main purpose of this document is to provide guidelines on the use of synthetic fiber ropes for offshore mooring applications. The secondary purpose of this document is to highlight differences between synthetic rope and traditional steel mooring systems, and to provide practical guidance on how to handle these differences during system design and installation.

The contents of this document should be used in conjunction with the most recent editions of API 2SK and API 2I, and other recommended practices and standards, as appropriate. Where the mooring design, construction and installation details are similar or equivalent to steel mooring systems, no further comments are included in this document.

This document reflects the latest learning from research, design, installation, and operation of synthetic fiber mooring components. The technology in synthetic fiber rope moorings continues to evolve. Designers are advised to take appropriate measures to ensure that their practices incorporate all research advances available to them.

The verbal forms used to express the provisions in this specification are as follows:

• the term "shall" denotes a minimum requirement to conform to the specification;

  
  

• the term "should" denotes a recommendation or that which is advised but not required to conform to the specification;

  
  

• the term "may" is used to express permission or a provision that is optional;

  
  

• the term "can" is used to express possibility or capability.

Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

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Suggested revisions are invited and should be submitted to the Standards Department, API, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001, standards@api.org.

iii

Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, Symbols, and Abbreviations 2

   1. Terms and Definitions 2

   2. Symbols and Abbreviations 8

4. Basic Considerations 9

   1. General 9

   2. Synthetic Fiber Ropes for Offshore Mooring 9

   3. Main Characteristics of Synthetic Fiber Ropes 10

5. Rope Design and Properties 11

   1. General 11

   2. Rope Material 11

   3. Rope Construction 13

   4. Rope Filter Barrier and Jacket 13

   5. Rope Termination 14

   6. Rope Properties 15

6. Mooring Design and Analysis 21

   1. General 21

   2. Mooring Configuration and Design 21

   3. Design Criteria 22

   4. Mooring Analysis 23

   5. Model Testing 31

7. Rope Specification and Testing 31

   1. General 31

   2. Rope Specification and Documentation 31

   3. Rope Testing 37

8. Rope Manufacture, Inspection, and Quality Assurance 40

   1. General 40

   2. Rope Fiber Material 40

   3. Rope Manufacturing 42

   4. Termination 42

   5. Assembly 42

   6. Inspection 43

   7. Quality Control and Assurance 44

9. Rope Storage, Handling and Installation 45

   1. General 45

   2. Storage, Handling, and Installation Specifications 45

   3. Storage, Handling, and Installation Considerations 46

   4. Installation Design Considerations 49

   5. Installation/Recovery Procedures 54

10. In-service Inspection and Maintenance 56

    1. General 56

    2. Destructive Inspection of Inserts 56

    3. Operations 56

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Contents

Page

Annex A (normative) Filter Barrier Particle Ingress Test 57

Annex B (normative) Testing of Rope Load-elongation Properties 59

Annex C (normative) Torque and Rotation Tests 86

Annex D (normative) Testing of Rope Tension-tension Fatigue Qualification 88

Annex E (normative) Testing of Rope Strength 90

Annex F (normative) Testing of Rope Axial Compression Performance 92

Annex G (informative) Polyester Mooring Analysis Example 94

Figures

1. Polyester Durability JIP, OTC 5720 and Fiber Tethers 2000 Fatigue Test Data, Compared with

   Wire Rope and Chain TN Curves from API 2SK 19

2. Polyester Rope Load-Elongation: Load-vs.-Extensometer 24

3. Idealized Polyester Behavior 26

4. Diagram of Eye Splice Showing Features 35

5. Typical Reel and Lifting Arrangement 47

6. Surface Buoys Tensioned Together to Maintain Fiber Rope in Tension 53

A.1 Grading of Sand for Particle Ingress Resistance Test 58

1. Idealized Synthetic Rope Elongation Behavior 61

2. Quasi-static Stiffness 73

3. Strain Component for DES/DER/Creep Test 85

1. Mooring Pattern for Identical Eight Line Equally Spaced Mooring System 95

2. Linear and Nonlinear Polyester Load-elongation Models 96

3. Maximum Vessel Offset, Nonlinear and Linear Load-elongation Curves 99

4. Maximum Tensions, Nonlinear and Linear Load-elongation Curves 100

5. Polyester Rope Delayed and Recoverable Elastic Stretch 101

6. Maximum Vessel Offsets for Three Nonlinear Moorings—Cases 1, 2-a, and 2-b 104

7. Maximum Tensions for Three Nonlinear Moorings—Cases 1, 2-a, and 2-b 104

Tables

1. Fiber Properties 11

2. Typical Rope Weights and Sizes for 10,000 kN Break Strength (including Jacket) 16

3. Typical Stiffness Values in EA/CBS 17

4. Fiber Rope Fatigue Curve Qualification Test Cycles 39

5. Resistance to Chemical and UV Radiation Damage 47

1. Mooring Line Properties, Eight Identical Lines 95

2. Anchor Distances and Grounded Lengths for Pretensions of 250 kips 96

3. Hurricane Metocean Conditions and Mean Loads for Return Periods between 5 and 40 Years 97

4. Maximum Vessel Offsets and Tensions—Nonlinear Load-Elongation Curves 98

5. Vessel Offsets for Four Linear Load-Elongation Curves 99

6. Un-stretched Total Polyester Rope Lengths, Outboard Wire Rope Lengths, and Pretensions

   for Three Moorings 102

7. Quiescent Equilibrium Vessel Offsets for Three Moorings 103

8. Maximum Vessel Offsets and Tensions for Three Moorings 103

vi

Design, Manufacture, Installation, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring

1. Scope

   
   

   1. This document applies to synthetic fiber ropes used in the form of taut leg or catenary moorings for both permanent and temporary offshore installations such as:

      
      

      1. monohull-based floating production, storage, and offloading units (FPSOs);

         
         

      2. monohull-based floating storage units (FSOs, FSUs);

         
         

      3. monohull or semi-submersible based floating production units (FPUs, FPSs);

         
         

      4. mobile offshore drilling units (MODUs);

         
         

      5. spar platforms;

         
         

      6. catenary anchor leg mooring (CALM) buoys (spread mooring only);

         
         

      7. mobile offshore units (MOUs, e.g., construction, pipelay, floating accommodation vessels).

      
      

   2. This document covers the following aspects of synthetic fiber ropes:

      
      

      1. design and analysis considerations of mooring system;

         
         

      2. design criteria for mooring components;

         
         

      3. rope design;

         
         

      4. rope specification and testing;

         
         

      5. rope manufacture and quality assurance;

         
         

      6. rope handling and installation;

         
         

      7. in-service inspection and maintenance.

      
      

   3. Application of this document to other offshore mooring applications is at the discretion of the designer and operator. This document is not intended to cover other marine applications of synthetic fiber ropes such as tanker mooring at piers and harbors, towing hawsers, mooring hawsers at single-point moorings (SPMs), and tension leg platform (TLP) tethers. Additionally, very little test data are available for large synthetic fiber ropes permanently deployed around fairleads and thus this document is limited to fiber ropes which span freely between end terminations.

      
      

2. Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document applies (including any addenda/errata).

API RP 2I, In-Service Inspection of Mooring Hardware for Floating Drilling Units

API RP 2SK, Design and Analysis of Stationkeeping Systems for Floating Structures

1