Planning, Designing, and Constructing Floating Production Systems

API RECOMMENDED PRACTICE 2FPS SECOND EDITION, OCTOBER 2011

REAFFIRMED, SEPTEMBER 2020

Special Notes

API publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed.

Neither API nor any of API's employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API's employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.

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

API publications are published to facilitate the broad availability of proven, sound engineering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices.

Any manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard.

Users of this Recommended Practice should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein.

All rights reserved. No part of this work may be reproduced, translated, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001.

Copyright © 2011 American Petroleum Institute

Foreword

API 2FPS is one of a series of API and other standards for offshore structures in the Gulf of Mexico. This suite of standards, hereby referenced as the API Floating Structures Standards (AFSS), are a suite of applicable "Working Stress Design" standards for structures to be deployed in U.S. waters. The suite consists of the following standards.

• API 2A-WSD, Planning, Designing and Constructing Fixed Offshore Platforms-Working Stress Design

• API Spec 2C, Specification for Offshore Cranes

• API RP 2D, Recommended Practice for Operation and Maintenance of Offshore Cranes

• API Bull 2INT-MET, Interim Guidance on Hurricane Conditions in the Gulf of Mexico

• API RP 2MOP, Marine Operations

• API RP 2RD, Recommended Practice for Design of Risers for Floating Production Systems (FPSs) and Tension- Leg Platforms (TLPs)

• API 2SIM, Structural Integrity Management of Fixed Offshore Structures

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

• API RP 2T, Recommended Practice for Planning, Design and Constructing Tension Leg Platforms

• API Bull 2U, Stability Design of Cylindrical Shells

• API Bull 2V, Design of Flat Plate Structures

• API RP 14J, Recommended Practice for Design and Hazards Analysis for Offshore Production Facilities

• API RP 75L, Guidance Document for the Development of a Safety and Environmental Management System for Onshore Oil and Natural Gas Production Operation and Associated Activities

• AISC 360-05, Specification for Structural Steel Buildings

• AWS D1.1, Structural Welding Code - Steel

The AFSS is deemed acceptable in regions that experience tropical cyclonic activity. Utilization of the AFSS in other regions can be acceptable if agreed by the owner and by the regulator, where one exists.

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.

Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the specification.

Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in order to conform to the specification.

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.

Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001.

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

Special Notes ii

Foreword iii

Introduction ix

1. Scope 1

2. Normative references 2

3. Terms and definitions 3

4. Symbols and abbreviated terms 8

   1. Symbols 8

   2. Abbreviated terms 10

5. Overall considerations 12

   1. Functional requirements 12

   2. Safety requirements 12

   3. Planning requirements 13

   4. Rules and regulations 14

   5. General requirements 14

   6. Independent verification 18

   7. Analytical tools 18

   8. In-service inspection and maintenance 19

   9. Assessment of existing floating structures 19

   10. Reuse of existing floating structures 24

6. Basic design requirements 24

   1. General 24

   2. Exposure levels 24

   3. Limit states 27

   4. Design situations 28

7. Actions and action effects 30

   1. General 30

   2. Permanent actions (G) 30

   3. Variable actions (Q) 31

   4. Accidental actions (A) 31

   5. Environmental actions (E). 32

   6. Other actions 40

   7. Repetitive actions 40

   8. Action combinations 41

8. Global analysis 41

   1. General 41

   2. Static and mean response analyses 41

   3. Global dynamic behaviour 42

   4. Frequency domain analysis 43

   5. Time domain analysis 44

   6. Uncoupled analysis 44

   7. Coupled analysis 44

   8. Resonant excitation and response 44

   9. Platform offset 44

   10. Air gap and wave assessment 45

   11. Platform motions and accelerations 45

   12. Model tests 46

   13. Design situations for structural analysis 46

9. Structural considerations 47

   1. General 47

      v

   2. Representative values of actions 47

   3. Design scantlings 49

   4. Modelling. 49

   5. Structural analysis 52

   6. Structural strength 53

   7. Design checks 54

   8. Special design issues 58

   9. Material 59

   10. Corrosion protection of steel 61

   11. Fabrication and construction 62

   12. Marine operations 63

   13. Topsides/hull interface 63

10. Fatigue analysis and design 64

    1. General 64

    2. Fatigue damage design safety factors 65

    3. Outline of approach 66

    4. Environmental data 67

    5. Structural modelling 67

    6. Hydrostatic analyses 67

    7. Response amplitude operators and combinations of actions 67

    8. Stresses and SCFs 68

    9. Stress range counting and distribution 68

    10. Fatigue resistance 68

    11. Damage accumulation 68

    12. Fracture mechanics methods 69

    13. Fatigue-sensitive components and connections 69

11. Monohulls 70

    1. General 70

    2. General design criteria 71

    3. Structural strength 72

12. Semi-submersibles 76

    1. General 76

    2. General design criteria 77

    3. Structural strength 77

13. Spars 78

    1. General 78

    2. General design requirements 78

    3. Structural strength 79

14. Conversion and reuse 80

    1. General 80

    2. Minimum design, construction and maintenance standards 80

    3. Pre-conversion structural survey 81

    4. Effects of prior service 81

    5. Corrosion protection and material suitability 82

    6. Inspection and maintenance 82

15. Hydrostatic stability and compartmentation 82

    1. General 82

    2. Inclining test 83

    3. Compartmentation 83

    4. Watertight and weathertight appliances 83

    5. Special requirements for monohulls 84

16. Mechanical systems 84

    1. General 84

    2. Hull systems 85

    3. Import and export systems 93

    4. Fire protection systems 96

17. Stationkeeping systems 97

    1. General 97

       vi

    2. Mooring equipment 97

    3. Turret 101

18. In-service inspection, monitoring and maintenance 102

    1. General 102

    2. Structural integrity management system philosophies 103

    3. Planning considerations 106

    4. Implementation issues 107

    5. Minimum requirements 110

19. Floating structure design and analysis—Other hulls 114

    1. General 114

    2. Structural steel design 114

    3. Stability and watertight integrity 114

Annex A (informative) Additional information and guidance 115

Annex B (normative) API Floating Structures Design Standards 182

Bibliography 183

vii

Introduction

The series of Standards applicable to types of offshore structure, constitutes a common basis covering those aspects that address design requirements and assessments of all offshore structures used by the petroleum, petrochemical and natural gas industries worldwide. Through their application the intention is to achieve reliability levels appropriate for manned and unmanned offshore structures, whatever the type of structure and the nature or combination of materials used.

It is important to recognize that structural integrity is an overall concept comprising models for describing actions, structural analyses, design rules, safety elements, workmanship, quality control procedures and national requirements, all of which are mutually dependent. The modification of one aspect of design in isolation can disturb the balance of reliability inherent in the overall concept or structural system. The implications involved in modifications, therefore, need to be considered in relation to the overall reliability of all offshore structural systems.

The series of Standards applicable to types of offshore structure is intended to provide wide latitude in the choice of structural configurations, materials and techniques without hindering innovation. Sound engineering judgment is therefore necessary in the use of these International Standards.

API 2FPS was developed in response to the offshore industry’s demand for a coherent and consistent definition of methodologies to design, analyse and assess floating offshore structures of the class described in Clause 1. In particular, this standard addresses monohulls, semi-submersibles and spars.

Some background to, and guidance on, the use of this standard is provided in informative Annex A. The clause numbering in Annex A is the same as in the normative text to facilitate cross-referencing.

ix

Planning, Designing, and Constructing Floating Production Systems

1 Scope

This document provides requirements and guidance for the structural design and/or assessment of floating offshore platforms used by the petroleum and natural gas industries to support the following functions:

• production;

  
  

• storage and/or offloading;

  
  

• drilling and production;

  
  

• production, storage and offloading;

  
  

• drilling, production, storage and offloading.

  
  

  NOTE 1 Floating offshore platforms are often referred to using a variety of abbreviations, e.g. FPS, FSU, FPSO, etc. (see Clauses 3 and 4), in accordance with their intended mission.

  
  

  NOTE 2 In this standard, the term “floating structure”, sometimes shortened to “structure”, is used as a generic term to indicate the structural systems of any member of the classes of platforms defined above.

  
  

  NOTE 3 In some cases, floating platforms are designated as “early production platforms”. This term relates merely to an asset development strategy. For the purposes of this International Standard, the term “production” includes “early production”.

  
  

  Its requirements do not apply to the structural systems of mobile offshore units (MOUs). These include, among others:

  
  

• floating structures intended primarily to perform drilling and/or well intervention operations (often referred to as MODUs), even when used for extended well test operations;

  
  

• floating structures used for offshore construction operations (e.g. crane barges or pipelay barges), for temporary or permanent offshore living quarters (floatels), or for transport of equipment or products (e.g. transportation barges, cargo barges), for which structures reference is made to relevant recognized classification society (RCS) rules.

  
  

  Its requirements are applicable to all possible life-cycle stages of the structures defined above, such as

  
  

• design, construction and installation of new structures, including requirements for inspection, integrity management and future removal,

  
  

• structural integrity management covering inspection and assessment of structures in-service, and

  
  

• conversion of structures for different use (e.g. a tanker converted to a production platform) or reuse at different locations.

The following types of floating structure are explicitly considered within the context of this standard:

1. monohulls (ship-shaped structures and barges);

   
   

2. semi-submersibles;

   
   

3. spars.

1