Underwater Inspection and Repair for Offshore Structures

Benefit from a much-needed, up-to-date handbook on underwater inspection and repair processes and technologies

Underwater Inspection and Repair for Offshore Structures fills a gap in the literature to provide an overview of the inspection and repair processes for both steel and concrete offshore structures. Authors and noted experts on the topic John V. Sharp and Gerhard Esdal guide readers through the reasons why inspection and repair are performed and how both are linked to the management of structural integrity, statutory requirements, and various types of damage.

The book addresses critical topics, including the execution and planning of inspection and repair, the tools and methods used, and their deployment underwater. The authors put particular focus on steel and concrete offshore oil and gas installations, but the content is also applicable to the substructures of offshore wind turbines. Underwater Inspection and Repair for Offshore Structures is complementary to the authors’ book Ageing and Life Extension of Offshore Structures, also from Wiley. This important book:

• Covers current inspection and monitoring techniques to evaluate existing structures
• Includes coverage of robotic (ROV) inspection and repair methods
• Provides an overview of repair and maintenance techniques applicable to the splash‑zone and underwater operations

Written for engineers, designers, and safety auditors working with offshore structures. Underwater Inspection and Repair for Offshore Structures is a comprehensive resource for understanding how to effectively inspect and repair these vulnerable structures.

John Sharp is a Visiting Professor at Cranfield University, UK. His main research interests include the ageing and life extension of structures and their inspection and repair. Formerly, he was responsible for the UK Health & Safety Executive’s offshore research programme.  

Gerhard Ersdal is a Professor in the Department of Mechanical and Structural Engineering and Material science at the University of Stavanger, Norway. His main research interests include structural integrity management, life extension of structures and risk management. 

1 INTRODUCTION TO UNDERWATER INSPECTION AND REPAIR 1

1.1 BACKGROUND 1

1.2 WHY DO WE INSPECT AND REPAIR STRUCTURES 2

1.3 TYPES OF OFFSHORE STRUCTURES 5

1.3.1 Fixed steel structures 7

1.3.2 Floating structures 7

1.3.3 Concrete platforms 8

1.4 OVERVIEW OF THIS BOOK 9

1.5 BIBLIOGRAPHIC NOTES 10

1.6 REFERENCES 10

2 STATUTORY REQUIREMENTS FOR INSPECTION AND REPAIR OF OFFSHORE STRUCTURES 11

2.1 INTRODUCTION 11

2.2 EXAMPLES OF COUNTRY STATUTORY REQUIREMENTS 12

2.2.1 Introduction 12

2.2.2 Regulation in US offshore industry 13

2.2.3 Regulation in UK offshore industry 13

2.2.4 Regulation in Norwegian offshore industry 14

2.3 STANDARDS AND RECOMMENDED PRACTICES FOR STEEL STRUCTURES 14

2.3.1 Introduction 14

2.3.2 API RP-2A and API RP-2SIM (Structural Integrity Management) 15

2.3.3 API RP-2FSIM (Floating Systems Integrity Management) 18

2.3.4 ISO 19902 19

2.3.5 ISO 19901-9 20

2.3.6 NORSOK N-005 20

2.4 STANDARDS AND RECOMMENDED PRACTICES FOR MOORING SYSTEMS 20

2.4.1 Introduction 20

2.4.2 API RP-2MIM (Mooring Integrity Management) 21

2.4.3 IACS Guideline for survey of offshore moorings 22

2.5 STANDARDS AND GUIDANCE NOTES FOR CONCRETE STRUCTURES 23

2.5.1 Introduction 23

2.5.2 ISO 19903 – concrete structures 23

2.5.3 Department of Energy Guidance Notes 27

2.5.4 NORSOK N-005 – concrete structures 28

2.6 DISCUSSION AND SUMMARY 29

2.7 REFERENCES 30

3 DAMAGE TYPES IN OFFSHORE STRUCTURES 33

3.1 INTRODUCTION 33

3.1.1 General 33

3.1.2 Corrosion 34

3.1.3 Cracking due to fatigue 36

3.1.4 Dents, bows and gauges due to impact 37

3.1.5 Cracking due to Hydrogen Embrittlement 37

3.1.6 Erosion, wear and tear 38

3.1.7 Brittle Fracture 38

3.1.8 Grout crushing and slippage 38

3.2 PREVIOUS STUDIES ON DAMAGE TO OFFSHORE STRUCTURES 38

3.3 PREVIOUS STUDIES ON DAMAGE TO FIXED STEEL STRUCTURES 39

3.3.1 MTD Underwater inspection of steel offshore structures 39

3.3.2 MTD Review of repairs to offshore structures and pipelines 41

3.3.3 PMB AIM project for MMS 41

3.3.4 HSE study on causes of damage to fixed steel structures 44

3.3.5 Single sided closure welds 45

3.3.6 MSL Rationalization and optimization of underwater inspection planning report 46

3.3.7 Studies on hurricane and storm damage 48

3.4 PREVIOUS STUDIES ON DAMAGE TO FLOATING STEEL STRUCTURES 51

3.4.1 D.En. studies on semi-submersibles 51

3.4.2 SSC review of damage types to ship shaped structures 51

3.4.3 Defect type for tanker structure components 52

3.4.4 Semisubmersible flooding incident data 53

3.5 PREVIOUS STUDIES ON DAMAGE TYPES TO MOORING LINES AND ANCHORS 54

3.5.1 Introduction and damage statistics for moorings 54

3.5.2 API RP-2MIM overview of damage types to mooring lines 55

3.5.3 HSE studies on mooring systems 56

3.5.4 Studies on corrosion of mooring systems 57

3.5.5 Studies on fatigue of mooring systems 58

3.6 PREVIOUS STUDIES ON CONCRETE STRUCTURES 59

3.6.1 Concrete in the Ocean project 59

3.6.2 Durability of offshore concrete structures 60

3.6.3 PSA study on damage to offshore concrete structures 60

3.7 PREVIOUS STUDIES ON MARINE GROWTH (MARINE FOULING) 62

3.8 SUMMARY OF DAMAGE AND ANOMALIES TO OFFSHORE STRUCTURES 64

3.8.1 General 64

3.8.2 Damage types specific to steel structures 65

3.8.3 Damage types specific to concrete structures 65

3.8.4 Summary table of damage to different types of structures 65

3.9 BIBLIOGRAPHIC NOTES 68

3.10 REFERENCES 68

4 INSPECTION METHODS FOR OFFSHORE STRUCTURES UNDERWATER 70

4.1 INTRODUCTION TO UNDERWATER INSPECTION 70

4.2 PREVIOUS STUDIES ON INSPECTION 72

4.2.1 Introduction 72

4.2.2 SSC survey of non-destructive test methods 72

4.2.3 Underwater inspection / testing / monitoring of offshore structures 74

4.2.4 HSE Handbook for underwater inspectors 75

4.2.5 MTD Underwater inspection of steel offshore structures 75

4.2.6 Department of Energy Fourth edition Guidance Notes on surveys 76

4.2.7 HSE Detection of damage to underwater tubulars and its effect on strength 77

4.2.8 MSL Rationalization and optimization of underwater inspection planning report 79

4.2.9 Projects on testing of inspection methods and their reliability 83

4.2.10 Concrete in the ocean programme 85

4.3 INSPECTION AND INSPECTION METHODS 89

4.3.1 Introduction 89

4.3.2 Visual inspection 90

4.3.3 Ultrasonic testing methods 92

4.3.4 Electromagnetic methods 93

4.3.5 Radiographic testing 95

4.3.6 Flooded member detection 95

4.3.7 Rebound hammer 97

4.3.8 Chloride ingress test 97

4.3.9 Electro-potential mapping 98

4.3.10 Cathodic protection inspection 99

4.4 DEPLOYMENT METHODS 101

4.4.1 Introduction 101

4.4.2 Divers 101

4.4.3 ROV and AUV 102

4.4.4 Splash zone access 105

4.4.5 Summary of inspection methods and their deployment 106

4.5 COMPETENCY OF INSPECTION PERSONNEL AND ORGANISATIONS 107

4.5.1 Introduction 107

4.5.2 Regulatory requirements on competency 107

4.5.3 Requirements on competency in standards 108

4.5.4 Certification and training of inspectors 109

4.5.5 Trials to study inspector competency 110

4.5.6 Organisational competency 110

4.6 RELIABILITY OF DIFFERENT INSPECTION METHODS UNDERWATER 112

4.7 INSPECTION OF FIXED STEEL STRUCTURES 114

4.8 INSPECTION OF CONCRETE STRUCTURES 117

4.9 INSPECTION OF FLOATING STRUCTURES AND MOORING SYSTEMS 120

4.10 REFERENCES 123

5 STRUCTURAL MONITORING METHODS 127

5.1 INTRODUCTION 127

5.1.1 General 127

5.1.2 Historical background 127

5.1.3 Requirements for monitoring in standards 130

5.2 PREVIOUS STUDIES ON STRUCTURAL MONITORING METHODS 131

5.2.1 MTD Underwater inspection of steel offshore installations 131

5.2.2 HSE review of structural monitoring 132

5.2.3 HSE updated review of structural monitoring 134

5.2.4 SIMoNET 136

5.3 STRUCTURAL MONITORING TECHNIQUES 136

5.3.1 Introduction 136

5.3.2 Acoustic emission technique 136

5.3.3 Leak detection 137

5.3.4 Global positioning systems and radar 137

5.3.5 Fatigue gauge 138

5.3.6 Continuous flooded member detection 138

5.3.7 Natural frequency monitoring 138

5.3.8 Strain Monitoring 139

5.3.9 Riser and anchor chain monitoring 140

5.3.10 Acoustic fingerprinting 140

5.3.11 Monitoring with guided waves 140

5.4 STRUCTURAL MONITORING CASE STUDY 140

5.5 SUMMARY ON STRUCTURAL MONITORING 141

5.6 BIBLIOGRAPHIC NOTES 143

5.7 REFERENCES 143

6 INSPECTION PLANNING, PROGRAMME AND DATA MANAGEMENT 145

6.1 INTRODUCTION 145

6.1.1 General 145

6.1.2 Long term inspection plan 146

6.1.3 Approaches for long-term inspection planning 148

6.1.4 Inspection programme 150

6.1.5 Integrity data management 151

6.1.6 Key performance Indicators 154

6.2 PREVIOUS STUDIES ON LONG-TERM PLANNING OF INSPECTIONS 155

6.2.1 PMB AIM project for MMS 155

6.2.2 MSL Rationalization and optimization of underwater inspection planning report 156

6.2.3 HSE study on the effects of local joint flexibility 157

6.2.4 HSE ageing plant report 157

6.2.5 Studies on risk based and probabilistic inspection planning 158

6.2.6 EI guide to risk based inspection planning 161

6.3 SUMMARY ON INSPECTION PLANNING AND PROGRAMME 162

6.3.1 Introduction 162

6.3.2 Fixed steel platforms 162

6.3.3 Floating steel structures 163

6.3.4 Concrete platforms 164

6.4 BIBLIOGRAPHIC NOTES 165

6.5 REFERENCES 165

7 EVALUATION OF DAMAGE AND ASSESSMENT OF STRUCTURES 168

7.1 INTRODUCTION 168

7.2 PREVIOUS STUDIES ON EVALUATION OF DAMAGED TUBULARS 170

7.2.1 Remaining fatigue life of cracked tubular structures 170

7.2.2 Static strength of cracked tubular structures 174

7.2.3 Effect of Multiple member failure 178

7.2.4 Corroded tubular members 179

7.2.5 Dent and bow damage to underwater tubulars and their effect on strength 183

7.2.6 Studies on assessment of system strength 187

7.2.7 PMB AIM project for MMS 188

7.2.8 MSL Significant JIP project for MMS 189

7.2.9 MSL Assessment of repair techniques for ageing or damaged structures 192

7.3 PREVIOUS STUDIES ON EVALUATION OF DAMAGED PLATED STRUCTURES 193

7.3.1 Introduction 193

7.3.2 SSC studies on residual strength of damaged plated marine structures 193

7.4 PREVIOUS STUDIES ON EVALUATION OF DAMAGED CONCRETE STRUCTURES 196

7.4.1 Department of energy assessment of major damage to the prestressed concrete tower 196

7.4.2 Department of Energy review of impact damage caused by dropped objects 197

7.4.3 HSE review of durability of prestressing components 197

7.4.4 HSE review of major hazards to concrete platforms 198

7.4.5 Department of Energy review of the effects of temperature gradients 198

7.4.6 Concrete in the oceans review of corrosion protection of concrete structures 198

7.4.7 Norwegian road administration guideline V441 199

7.5 PRACTICE OF EVALUATION AND ASSESSMENT OF OFFSHORE STRUCTURES 200

7.5.1 General 200

7.5.2 Fixed and floating steel structures 202

7.5.3 Concrete structures 205

7.6 REFERENCES 206

8 REPAIR AND MITIGATION OF OFFSHORE STRUCTURES 212

8.1 INTRODUCTION TO UNDERWATER REPAIR 212

8.2 PREVIOUS GENERIC STUDIES ON REPAIR OF STRUCTURES 214

8.2.1 UEG report on repair to North Sea offshore structures 214

8.2.2 MTD study on repairs of offshore structures 214

8.2.3 UK Department of Energy Fourth edition Guidance Notes 218

8.2.4 DNV GL study on repair methods for PSA 219

8.3 PREVIOUS STUDIES ON REPAIR OF TUBULAR STRUCTURES 221

8.3.1 Grout repairs to steel offshore structures 221

8.3.2 UK Joint Industry Repairs Research Project 223

8.3.3 UK Department of Energy and TWI study on repair methods for fixed offshore structures 224

8.3.4 UK Department of Energy funded work on adhesive repairs 229

8.3.5 Residual and fatigue strength of grout filled damaged tubular members 231

8.3.6 Fatigue Life Enhancement of Tubular Joints by Grout Injection. 232

8.3.7 ATLSS projects on repair to dent damaged tubular members 232

8.3.8 ATLSS projects on repair to corrosion damaged tubulars 234

8.3.9 MSL Strengthening, modification and repair of offshore installations 235

8.3.10 MSL Underwater structural repairs using composite materials 237

8.3.11 HSE Experience from the use of clamps offshore 238

8.3.12 MSL study on neoprene lined clamps 240

8.3.13 MSL Repair techniques for ageing and damaged structures 240

8.3.14 MMS studies on hurricane damage and repair 244

8.3.15 BOEME report on wet weld repairs to US structures 244

8.4 PREVIOUS STUDIES ON REPAIR OF CONCRETE STRUCTURES 246

8.4.1 Introduction 246

8.4.2 Repair of major damage to concrete offshore structures 247

8.4.3 Scaling of underwater concrete repairs 248

8.4.4 Assessment of Materials for Repair of Damaged Concrete Underwater 249

8.4.5 Effectiveness of concrete repairs 254

8.5 PREVIOUS STUDIES ON REPAIR OF PLATED STRUCTURES 255

8.6 REPAIR OF STEEL STRUCTURES 258

8.6.1 Introduction 258

8.6.2 Selection of mitigation and repair methods 259

8.6.3 Machining methods (grinding) 262

8.6.4 Re-melting methods 264

8.6.5 Weld residual stress improvement methods (peening) 265

8.6.6 Stop holes and crack deflecting holes 265

8.6.7 Structural modifications 268

8.6.8 Underwater welding 268

8.6.9 Doubler plates 272

8.6.10 Removal of structural elements 272

8.6.11 Bonded type repairs 273

8.6.12 Structural clamps and sleeves 274

8.6.13 Grout filling of members 277

8.6.14 Grout filling of tubular joints 278

8.6.15 Installation of new structural elements 279

8.6.16 Summary of steel repairs 280

8.7 REPAIR OF CORROSION AND CORROSION PROTECTION SYSTEMS 283

8.7.1 Introduction 283

8.7.2 Repair of damaged coatings 283

8.7.3 Replacement of material 284

8.7.4 Repair or replacement of the corrosion protection system 284

8.8 REPAIR OF MOORING SYSTEMS 285

8.9 REPAIR OF CONCRETE STRUCTURES 286

8.9.1 Introduction 286

8.9.2 Choice of repair method 288

8.9.3 Concrete material replacement 288

8.9.4 Injection methods 291

8.9.5 Repair of reinforcement and prestressing tendons 292

8.9.6 Summary of concrete repairs 292

8.10 OVERVIEW OF OTHER MITIGATION METHODS 293

8.11 BIBLIOGRAPHIC NOTES 294

8.12 REFERENCES 294

9 CONCLUSIONS AND FUTURE POSSIBILITIES 300

9.1 OVERVIEW OF THE BOOK 300

9.2 EMERGING TECHNOLOGIES 300

9.3 FINAL THOUGHTS 302

9.4 REFERENCES 303

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