Description: ALWC is a particularly aggressive and localised form of low water corrosion which can occur in tidal and brackish waters on steel maritime structures. Corrosion rates in regions affected by ALWC can be 1mm/side/year or more and design corrosion allowances will, therefore, be exceeded quickly. ALWC could lead to a loss of 33% to 66% of the asset value. This process will rapidly compromise the integrity of affected structures and will lead to significant costs for repair or replacement, in addition to having serious implications for the safe operation of the structure.

This Report provides a comprehensive guide to the phenomenon of ALWC and its management, condition appraisal, repair, protection and monitoring. It is aimed at infrastructure owners, operators and their advisors, specialist engineers and asset and maintenance managers in ports, harbours and other marine locations. An Executive Summary gives an overview of the report and answers key questions. More in-depth information can be gained from reading the whole report, particular chapters of interest or the detailed information in the appendices.

It is based on a detailed review of published literature and infrastructure owner’s procedures, consultation with experts and practitioners from a cross section of fields of expertise and case studies demonstrating good practice.

Keywords: coastal and marine, water infrastructure

Contents: Summary 2, Executive summary 7, Contents 12, List of figures 15, List of plates 16, List of tables 17, List of boxes 18, Abbreviations 19, 1 INTRODUCTION, 1.1 Background 21, 1.2 Purpose and scope of work 22, 1.3 Applications and types of structure at risk 23, 1.4 Implications of ALWC to structures 25, 1.5 Brief overview of Health and Safety legislation 26, 1.6 Environmental responsibilities 27, SUMMARY 29 2 BACKGROUND TO ALWC 30, 2.1 Traditional marine corrosion 30, 2.2 Common forms of localised corrosion 32, 2.3 Accelerated low water corrosion 34, 2.3.1 Identification 35, 2.3.2 Influencing factors 38, 2.3.3 Mechanism 39, 2.4 Corrosion rate data 41, SUMMARY 45, 3 GEOGRAPHIC DISTRIBUTION OF ALWC 46, 3.1 Geographic areas at risk 46, 3.2 UK surveys 46, SUMMARY 48, 4 ASSET MANAGEMENT FOR ALWC 49, 4.1 Consequences of loss of performance 49, 4.2 Legal implications under Health and Safety legislation 51, 4.3 Economic considerations 51, 4.4 Whole life asset cost (cost effective long-term management strategies) 53, 4.5 Residual capacity and service life assessment 53, 4.6 Maintenance strategy 54, 4.61 Data management 54, 4.7 Risk assessment methods 55, 4.7.1 Risk assessment methods – small asset owner 57, 4.7.2 Risk assessment methods – large asset owner 57, SUMMARY 58, 5 CONDITION APPRAISAL 59, 5.1 Requirement for condition appraisal 59, 5.2 Appraisal methodology 60, 5.2.1 Methodology 60, 5.2.2 Personnel 62, 5.2.3 Desktop study 62, 5.2.4 Planning 62, 5.2.5 Initial inspection 63, 5.2.6 Preliminary analysis 67, 5.2.7 Detailed survey 67, 5.2.8 Detailed analysis 70, 5.2.9 Ongoing monitoring inspections 73, SUMMARY 74, 6 REPAIR AND PROTECTION 75, 6.1 Selection of strategy for repair 75, 6.2 Repair techniques for ALWC 77, 6.2.1 Skeletal structures 77, 6.2.2 Solid structures 80, 6.3 Access to carry out works 84, 6.3.1 Underwater repairs 85, 6.3.2 Dry repairs 86, 6.4 Corrosion implications of repairs 86, 6.5 Protection options for new build and existing structures 87, 6.5.1 Protection methods 89, 6.5.2 Protection strategies for new build structures 95, 6.5.3 Protection strategies for existing structures 96, SUMMARY 97, 7 MONITORING OF PERFORMANCE OF PREVENTATIVE, REMEDIAL AND STRENGTHENING MEASURES 102, 7.1 Monitoring methods 102, 7.2 Post implementation assessment and evaluation 102, SUMMARY 110, 8 ALWC PROJECT PROCUREMENT AND MANAGEMENT 111, 8.1 Strategy for survey and works 111, 8.1.1 Separate survey and works contracts 111, 8.1.2 Combined survey and works contracts 111, 8.2 Contractual and commercial issues 112, .2.1 Method of payment and form of contract 112, 8.2.2 Selection of method of payment and contract form 113, 8.2.3 Supervision and quality control 113, 8.2.4 Prioritisation and contingency and scope of work 114, 8.2.5 Interaction with normal facility operations 114, 8.2.6 Programming and urgency 115, 8.2.7 Invitation of tenders 115, 8.2.8 Tender and contract documentation 115, 8.2.9 Selection of contractor 117, 9 AREAS REQUIRING FURTHER RESEARCH 118, 9.1 Research topics 118, 9.1.1 Mechanism(s) for ALWC 118, 9.1.2 Protection steel against ALWC 119, 9.1.3 Identification of ALWC 119, 9.1.4 Monitoring of ALWC 120, 9.1.5 Assessment of ALWC structures 120, 9.1.6 Predictive model 120, 9.2 New developments 120, 10 RECOMMENDATIONS FOR GOOD PRACTICE 121, 11 REFERENCES 123, APPENDICES 130, Appendix 1 Corrosion reactions of steel in seawater 131, Appendix 2 Marine corrosion 132, Appendix 3 Findings of previous research studies on ALWC 142, Appendix 4 Risk assessment model for ALWC 146, Appendix 5 Copy of CIRIA questionnaire 147, Appendix 6 Preliminary analysis of CIRIA questionnaire data 159, Appendix 7 Surveying and monitoring 164, Appendix 8 Contents of a typical detailed condition appraisal report 174, Appendix 9 A model generic risk assessment 175, Appendix 10 Corrosion protection methods 178, Appendix 11 ALWC case studies 198, BIBLIOGRAPHY 204, GLOSSARY 212