Ageing and Life Extension of Offshore Structures: The Challenge of Managing Structural Integrity

A comprehensive overview of managing and assessing safety and functionality of ageing offshore structures and pipelines A significant proportion, estimated at over 50%, of the worldwide infrastructure of offshore structures and pipelines is in a life extension phase and is vulnerable to ageing processes. This book captures the central elements of the management of ageing offshore structures and pipelines in the life extension phase. The book gives an overview of: the relevant ageing processes and hazards; how ageing processes are managed through the life cycle, including an overview of structural integrity management; how an engineer should go about assessing a structure that is to be operated beyond its original design life, and how ageing can be mitigated for safe and effective continued operation. Key Features: Provides an understanding of ageing processes and how these can be mitigated. Applies engineering methods to ensure that existing structures can be operated longer rather than decommissioned unduly prematurely. Helps engineers performing these tasks in both evaluating the existing structures and maintaining ageing structures in a safe manner. The book gives an updated summary of current practice and research on the topic of the management of ageing structures and pipelines in the life extension phase but also meets the needs of structural engineering students and practicing offshore and structural engineers in oil & gas and engineering companies. In addition, it should be of value to regulators of the offshore industry.

Table of Contents:
Preface xi Definitions xiii 1 Introduction to Ageing of Structures 1 1.1 Structural Engineering and Ageing Structures 1 1.2 History of Offshore Structures Worldwide 4 1.3 Failure Statistics for Ageing Offshore Structures 8 1.3.1 Introduction 8 1.3.2 Failure Statistics of Offshore Structures 8 1.3.3 Experience from Land Based Structures 9 1.3.4 Experience from Offshore Fixed Steel Structures 10 1.3.5 Experience from the Shipping and Mobile Offshore Unit Industries 14 1.4 The Terms ‘Design Life’ and ‘Life Extension’ and the Bathtub Curve 15 1.5 Life Extension Assessment Process 18 References 20 2 Historic and Present Principles for Design, Assessment and Maintenance of Offshore Structures 23 2.1 Historic Development of Codes and Recommended Practices 23 2.1.1 US Recommended Practices and Codes 23 2.1.2 UK Department of Energy and HSE Guidance Notes 24 2.1.3 Norwegian Standards 26 2.1.4 ISO Standards 27 2.2 Current Safety Principles Applicable to Structural Integrity 28 2.2.1 Introduction 28 2.2.2 Application of Safety Principles to Structures 29 2.2.2.1 General 29 2.2.2.2 Partial Factor and Limit State Design Method 30 2.2.2.3 Robustness 32 2.2.2.4 Design Analysis Methods 34 2.2.2.5 Management of Structures in Operation 35 2.2.3 Managing Safety 35 2.2.4 Change Management 38 2.3 Current Regulation and Requirements for Ageing and Life Extension 38 2.3.1 Regulatory Practice in the UK for Ageing and Life Extension 38 2.3.2 Regulatory Practice in Norway Regarding Life Extension 40 2.3.3 Regulatory Practice in the USA 41 2.3.4 Regulatory Practice Elsewhere in the World 42 2.4 Structural Integrity Management 43 2.4.1 Introduction 43 2.4.2 The Main Process of Structural Integrity Management 45 2.4.3 Evolution of Structural Integrity Management 47 2.4.3.1 The Early Years 47 2.4.3.2 The Introduction of Structural Integrity Management into Standards 47 2.4.4 Current SIM Approach 47 2.4.5 Incident Response and Emergency Preparedness 51 2.4.6 SIM in Life Extension 52 References 53 3 Ageing Factors 57 3.1 Introduction 57 3.1.1 Physical Changes 59 3.1.2 Structural Information Changes 59 3.1.3 Changes to Knowledge and Safety Requirements 60 3.1.4 Technological Changes 61 3.2 Overview of Physical Degradation Mechanisms in Materials 62 3.3 Material Degradation 63 3.3.1 Introduction 63 3.3.2 Overview of Physical Degradation for Types of Steel Structures 64 3.3.3 Steel Degradation 65 3.3.3.1 Hardening Due to Plastic Deformation 65 3.3.3.2 Hydrogen Embrittlement 66 3.3.3.3 Erosion 68 3.3.3.4 Wear and Tear 68 3.3.4 Concrete Degradation 68 3.3.4.1 Concrete Strength in Ageing Structures 68 3.3.4.2 General 70 3.3.4.3 Bacterial Induced Deterioration 71 3.3.4.4 Thermal Effects 72 3.3.4.5 Erosion 72 3.4 Corrosion 73 3.4.1 General 73 3.4.2 External Corrosion 73 3.4.3 Various Forms of Corrosion 74 3.4.3.1 CO2 Corrosion 74 3.4.3.2 Environmental Cracking Due to H2S 74 3.4.3.3 Microbiologically Induced Corrosion 74 3.4.4 Special Issues Related to Corrosion in Hulls and Ballast Tanks 75 3.4.5 Concrete Structures 75 3.4.5.1 Corrosion of Steel Reinforcement 75 3.4.5.2 Corrosion of Prestressing Tendons 77 3.5 Fatigue 77 3.5.1 Introduction 77 3.5.2 Factors Influencing Fatigue 80 3.5.3 Implications of Fatigue Damage 81 3.5.4 Fatigue Issues with High Strength Steels 83 3.5.5 Fatigue Research 84 3.6 Load Changes 85 3.6.1 Marine Growth 85 3.6.2 Subsidence andWave in Deck 86 3.7 Dents, Damages, and Other Geometrical Changes 86 3.8 Non-physical Ageing Changes 88 3.8.1 Technological Changes (Obsolescence) 88 3.8.2 Structural Information Changes 89 3.8.3 Knowledge and Safety Requirement Changes 90 References 91 4 Assessment of Ageing and Life Extension 95 4.1 Introduction 95 4.1.1 Assessment versus Design Analysis 96 4.2 Assessment Procedures 97 4.2.1 Introduction 97 4.2.2 Brief Overview of ISO 19902 99 4.2.3 Brief Overview of NORSOK N-006 101 4.2.4 Brief Overview of API RP 2A-WSD 102 4.2.5 Brief Overview of ISO 13822 102 4.2.6 Discussion of These Standards 103 4.3 Assessment of Ageing Materials 104 4.4 Strength Analysis 107 4.4.1 Introduction 107 4.4.2 Strength and Capacity of Damaged Steel Structural Members 108 4.4.2.1 Effect of Metal Loss andWall Thinning 109 4.4.2.2 Effect of Cracking and Removal of Part of Section 110 4.4.2.3 Effect of Changes to Material Properties 110 4.4.2.4 Effect of Geometric Changes 110 4.4.2.5 Methods for Calculating the Capacity of Degraded Steel Members 110 4.4.3 Strength and Capacity of Damaged Concrete Structural Members 111 4.4.4 Non-Linear Analysis of Jacket of Structures (Push-Over Analysis) 113 4.5 Fatigue Analysis and the S–N Approach 115 4.5.1 Introduction 115 4.5.2 Methods for Fatigue Analysis 116 4.5.3 S–N Fatigue Analysis 117 4.5.3.1 Fatigue Loads and Stresses to be Considered 117 4.5.3.2 Fatigue Capacity Based on S–N Curves 119 4.5.3.3 Damage Calculation 121 4.5.3.4 Safety consideration by Design Fatigue Factors 122 4.5.4 Assessment of Fatigue for Life Extension 122 4.5.4.1 Introduction 122 4.5.4.2 High Cycle/Low Stress Fatigue 123 4.5.4.3 Low Cycle/High Stress Fatigue 124 4.6 FractureMechanics Assessment 126 4.6.1 Introduction 126 4.6.2 Fatigue Crack Growth Analysis 128 4.6.3 Fracture Assessment 131 4.6.4 Fracture Toughness Data 132 4.6.5 Residual Stress Distribution 132 4.6.6 Application of Fracture Mechanics to Life Extension 132 4.7 Probabilistic Strength, Fatigue, and Fracture Mechanics 134 4.7.1 Introduction 134 4.7.2 Structural Reliability Analysis – Overview 135 4.7.3 Decision Making Based on Structural Reliability Analysis 136 4.7.4 Assessment of Existing Structures by Structural Reliability Analysis 138 References 139 5 Inspection and Mitigation of Ageing Structures 143 5.1 Introduction 143 5.2 Inspection 144 5.2.1 Introduction 144 5.2.2 The Inspection Process 145 5.2.3 Inspection Philosophies 147 5.2.4 Risk and Probabilistic Based Inspection Planning 148 5.2.5 Inspection of Fixed Jacket Structures 150 5.2.6 Inspection of Floating Structures 154 5.2.7 Inspection of Topside Structures 155 5.2.8 Structural Monitoring 158 5.3 Evaluation of Inspection Findings 160 5.4 Mitigation of Damaged Structures 161 5.4.1 Introduction 161 5.4.2 Mitigation of Corrosion Damage 163 5.4.3 Mitigation of the Corrosion Protection System 163 5.4.4 Mitigation of Fatigue and Other Damage 166 5.5 Performance of Repaired Structures 168 5.5.1 Introduction 168 5.5.2 Fatigue Performance of Repaired Tubular Joints 168 5.5.3 Fatigue Performance of Repaired Plated Structures 170 References 171 6 Summary and Further Thoughts 173 6.1 Ageing Structures and Life Extension 173 6.2 FurtherWork and Research Needs Related to Ageing Structures 174 6.3 Final Thoughts 176 A Types of Structures 177 A.1 Fixed Platforms 177 A.2 Floating Structures 177 Reference 179 B InspectionMethods 181 B.1 General Visual Inspection 181 B.2 Close Visual Inspection 181 B.3 FloodedMember Detection 181 B.4 Ultrasonic Testing 182 B.5 Eddy Current Inspection 182 B.6 Magnetic Particle Inspection 182 B.7 Alternating Current Potential Drop 182 B.8 Alternating Current Field Measurement 182 B.9 Acoustic Emission Monitoring 183 B.10 Leak Detection 183 B.11 Air Gap Monitoring 183 B.12 Strain Monitoring 183 B.13 Structural Monitoring 184 C Calculation Examples 185 C.1 Example of Closed Form Fatigue Calculation 185 C.2 Example of Application of Fracture Mechanics to Life Extension 186 Index 191