Ageing and Life Extension of Offshore Structures

Gerhard Ersdal has had an interest in existing structures and especially the safety of older structures for most of his engineering career. He received his MSc in structural engineering in 1991 and then worked for eight years in a major engineering company in Norway, (Multiconsult) designing primarily offshore structures and bridges and also working on the restoration of many historic buildings in Norway. In 1999, he joined the Norwegian Petroleum Directorate and conducted research on the safety of older offshore structures in a PhD programme at the University of Stavanger. He received his PhD on life extension of ageing offshore structures in 2005. He is the project manager for the Norwegian Petroleum Safety Authority's Ageing and Life Extension research programme, with responsibility for several workshops, conferences and papers on the topic. In 2013, he was awarded a professorship at the University in Stavanger on ageing and life extension of structures. Prof. John V. Sharp has over 35 years' experience in offshore & marine engineering, with particular interests in offshore technology, safety, life extension, structural integrity, risk management and renewable energy. He was responsible for the UK Health & Safety Executive's £6M offshore health & safety research programme between 1993 and 1996, with particular interests in structural integrity and risk management. He has been a Visiting Professor at Cranfield University since 1996, which includes lecturing and teaching on Master's Courses on offshore engineering and renewables (offshore wind, wave and tidal). Sharp is also a Commissioner for Alderney Commission for Renewable Energy (since 2010), with specific interests in tidal energy. He has also undertaken consultancy work for a number of organisations, which has included assessment and management of ageing offshore installations, life extension, performance indicator measures for organisational capability for both structural integrity and asset maintenance. Dr. Alexander Stacey is a Structural Integrity Specialist Inspector in the Energy Division of the Hazardous Installations Directorate of the UK Health & Safety Executive. He graduated from the University of London's Imperial College with a degree in Mechanical Engineering and a Ph.D. on research in fatigue and fracture mechanics. He was subsequently employed as a Fracture Mechanics Specialist in the Offshore Division of Lloyd's Register. In his current role as a Structural Integrity Specialist in the Energy Division of the Health and Safety Executive, his primary interest is the structural integrity management of offshore installations throughout the lifecycle. Principal activities include the inspection of duty holders' structural integrity management systems, the assessment of safety cases, the development of guidance, codes and standards and supporting R&D. A key area of interest is the management of ageing and life extension of the UK's offshore infrastructure.

• Preface xiDefinitions xiii1 Introduction to Ageing of Structures 11.1 Structural Engineering and Ageing Structures 11.2 History of Offshore Structures Worldwide 41.3 Failure Statistics for Ageing Offshore Structures 81.3.1 Introduction 81.3.2 Failure Statistics of Offshore Structures 81.3.3 Experience from Land Based Structures 91.3.4 Experience from Offshore Fixed Steel Structures 101.3.5 Experience from the Shipping and Mobile Offshore Unit Industries 141.4 The Terms ‘Design Life’ and ‘Life Extension’ and the Bathtub Curve 151.5 Life Extension Assessment Process 18References 202 Historic and Present Principles for Design, Assessment and Maintenance of Offshore Structures 232.1 Historic Development of Codes and Recommended Practices 232.1.1 US Recommended Practices and Codes 232.1.2 UK Department of Energy and HSE Guidance Notes 242.1.3 Norwegian Standards 262.1.4 ISO Standards 272.2 Current Safety Principles Applicable to Structural Integrity 282.2.1 Introduction 282.2.2 Application of Safety Principles to Structures 292.2.2.1 General 292.2.2.2 Partial Factor and Limit State Design Method 302.2.2.3 Robustness 322.2.2.4 Design Analysis Methods 342.2.2.5 Management of Structures in Operation 352.2.3 Managing Safety 352.2.4 Change Management 382.3 Current Regulation and Requirements for Ageing and Life Extension 382.3.1 Regulatory Practice in the UK for Ageing and Life Extension 382.3.2 Regulatory Practice in Norway Regarding Life Extension 402.3.3 Regulatory Practice in the USA 412.3.4 Regulatory Practice Elsewhere in the World 422.4 Structural Integrity Management 432.4.1 Introduction 432.4.2 The Main Process of Structural Integrity Management 452.4.3 Evolution of Structural Integrity Management 472.4.3.1 The Early Years 472.4.3.2 The Introduction of Structural Integrity Management into Standards 472.4.4 Current SIM Approach 472.4.5 Incident Response and Emergency Preparedness 512.4.6 SIM in Life Extension 52References 533 Ageing Factors 573.1 Introduction 573.1.1 Physical Changes 593.1.2 Structural Information Changes 593.1.3 Changes to Knowledge and Safety Requirements 603.1.4 Technological Changes 613.2 Overview of Physical Degradation Mechanisms in Materials 623.3 Material Degradation 633.3.1 Introduction 633.3.2 Overview of Physical Degradation for Types of Steel Structures 643.3.3 Steel Degradation 653.3.3.1 Hardening Due to Plastic Deformation 653.3.3.2 Hydrogen Embrittlement 663.3.3.3 Erosion 683.3.3.4 Wear and Tear 683.3.4 Concrete Degradation 683.3.4.1 Concrete Strength in Ageing Structures 683.3.4.2 General 703.3.4.3 Bacterial Induced Deterioration 713.3.4.4 Thermal Effects 723.3.4.5 Erosion 723.4 Corrosion 733.4.1 General 733.4.2 External Corrosion 733.4.3 Various Forms of Corrosion 743.4.3.1 CO2 Corrosion 743.4.3.2 Environmental Cracking Due to H2S 743.4.3.3 Microbiologically Induced Corrosion 743.4.4 Special Issues Related to Corrosion in Hulls and Ballast Tanks 753.4.5 Concrete Structures 753.4.5.1 Corrosion of Steel Reinforcement 753.4.5.2 Corrosion of Prestressing Tendons 773.5 Fatigue 773.5.1 Introduction 773.5.2 Factors Influencing Fatigue 803.5.3 Implications of Fatigue Damage 813.5.4 Fatigue Issues with High Strength Steels 833.5.5 Fatigue Research 843.6 Load Changes 853.6.1 Marine Growth 853.6.2 Subsidence andWave in Deck 863.7 Dents, Damages, and Other Geometrical Changes 863.8 Non-physical Ageing Changes 883.8.1 Technological Changes (Obsolescence) 883.8.2 Structural Information Changes 893.8.3 Knowledge and Safety Requirement Changes 90References 914 Assessment of Ageing and Life Extension 954.1 Introduction 954.1.1 Assessment versus Design Analysis 964.2 Assessment Procedures 974.2.1 Introduction 974.2.2 Brief Overview of ISO 19902 994.2.3 Brief Overview of NORSOK N-006 1014.2.4 Brief Overview of API RP 2A-WSD 1024.2.5 Brief Overview of ISO 13822 1024.2.6 Discussion of These Standards 1034.3 Assessment of Ageing Materials 1044.4 Strength Analysis 1074.4.1 Introduction 1074.4.2 Strength and Capacity of Damaged Steel Structural Members 1084.4.2.1 Effect of Metal Loss andWall Thinning 1094.4.2.2 Effect of Cracking and Removal of Part of Section 1104.4.2.3 Effect of Changes to Material Properties 1104.4.2.4 Effect of Geometric Changes 1104.4.2.5 Methods for Calculating the Capacity of Degraded Steel Members 1104.4.3 Strength and Capacity of Damaged Concrete Structural Members 1114.4.4 Non-Linear Analysis of Jacket of Structures (Push-Over Analysis) 1134.5 Fatigue Analysis and the S–N Approach 1154.5.1 Introduction 1154.5.2 Methods for Fatigue Analysis 1164.5.3 S–N Fatigue Analysis 1174.5.3.1 Fatigue Loads and Stresses to be Considered 1174.5.3.2 Fatigue Capacity Based on S–N Curves 1194.5.3.3 Damage Calculation 1214.5.3.4 Safety consideration by Design Fatigue Factors 1224.5.4 Assessment of Fatigue for Life Extension 1224.5.4.1 Introduction 1224.5.4.2 High Cycle/Low Stress Fatigue 1234.5.4.3 Low Cycle/High Stress Fatigue 1244.6 FractureMechanics Assessment 1264.6.1 Introduction 1264.6.2 Fatigue Crack Growth Analysis 1284.6.3 Fracture Assessment 1314.6.4 Fracture Toughness Data 1324.6.5 Residual Stress Distribution 1324.6.6 Application of Fracture Mechanics to Life Extension 1324.7 Probabilistic Strength, Fatigue, and Fracture Mechanics 1344.7.1 Introduction 1344.7.2 Structural Reliability Analysis – Overview 1354.7.3 Decision Making Based on Structural Reliability Analysis 1364.7.4 Assessment of Existing Structures by Structural Reliability Analysis 138References 1395 Inspection and Mitigation of Ageing Structures 1435.1 Introduction 1435.2 Inspection 1445.2.1 Introduction 1445.2.2 The Inspection Process 1455.2.3 Inspection Philosophies 1475.2.4 Risk and Probabilistic Based Inspection Planning 1485.2.5 Inspection of Fixed Jacket Structures 1505.2.6 Inspection of Floating Structures 1545.2.7 Inspection of Topside Structures 1555.2.8 Structural Monitoring 1585.3 Evaluation of Inspection Findings 1605.4 Mitigation of Damaged Structures 1615.4.1 Introduction 1615.4.2 Mitigation of Corrosion Damage 1635.4.3 Mitigation of the Corrosion Protection System 1635.4.4 Mitigation of Fatigue and Other Damage 1665.5 Performance of Repaired Structures 1685.5.1 Introduction 1685.5.2 Fatigue Performance of Repaired Tubular Joints 1685.5.3 Fatigue Performance of Repaired Plated Structures 170References 1716 Summary and Further Thoughts 1736.1 Ageing Structures and Life Extension 1736.2 FurtherWork and Research Needs Related to Ageing Structures 1746.3 Final Thoughts 176A Types of Structures 177A.1 Fixed Platforms 177A.2 Floating Structures 177Reference 179B InspectionMethods 181B.1 General Visual Inspection 181B.2 Close Visual Inspection 181B.3 FloodedMember Detection 181B.4 Ultrasonic Testing 182B.5 Eddy Current Inspection 182B.6 Magnetic Particle Inspection 182B.7 Alternating Current Potential Drop 182B.8 Alternating Current Field Measurement 182B.9 Acoustic Emission Monitoring 183B.10 Leak Detection 183B.11 Air Gap Monitoring 183B.12 Strain Monitoring 183B.13 Structural Monitoring 184C Calculation Examples 185C.1 Example of Closed Form Fatigue Calculation 185C.2 Example of Application of Fracture Mechanics to Life Extension 186Index 191