GUIDELINES FOR THE INSPECTION AND MAINTENANCE OF DOUBLE HULL TANKER STRUCTURES Issued by: Tanker Structure Co-operative Forum in association with International Association of Classi? cation Societies Published and Printed in England by Witherby Seamanship International Ltd. 4 Dunlop Square, Deans Estate, Livingston, EH 54 85B, West Lothian, UK. WSIL 047 - Guidelines for the Inspection and Maintenance.indd iWSIL 047 - Guidelines for the Inspection and Maintenance.indd i8/29/2008 12:52:02 PM8/29/2008 12:52:02 PM ii other books in the series Guidance Manual for the Inspection and Condition Assessment of Tanker Structures Condition, Evaluation and Maintenance of Tanker Structures First published 1995 by Witherby Seamanship International Ltd. 4 Dunlop Square, Deans Estate, Livingston, EH 54 85B, West Lothian, UK. Tel. No.: +44 (0) 1506 463 227 Fax No.: +44 (0) 1506 468 999 E-mail: info@witherbyseamanship.com www: witherbyseamanship.com © International Chamber of Shipping, London and Oil Companies International Marine Forum, Bermuda ISBN 13: 978 1 85609 080 3 ISBN 10: 1 85609 080 9 British Library Cataloguing in Publication Data Guidelines for the Inspection and Maintenance of Double Hull Tanker Structures ISBN 1 85609 080 9 Notice of Terms of Use The Tanker Structure Co-operative Forum grants permission to reproduce a limited portion of this publication’s contents for educational uses, or other purposes which serve to enhance the safety and durability of tanker structures. Any extract of this publication’s contents is to suitably recognize the Tanker Structure Co-operative Forum and the title of this publication as the source of the extracted material; and the publisher’s name and address is also to be provided. WSIL 047 - Guidelines for the Inspection and Maintenance.indd iiWSIL 047 - Guidelines for the Inspection and Maintenance.indd ii8/29/2008 12:52:02 PM8/29/2008 12:52:02 PM iii CONTENTS Page 1. INTRODUCTION 1 2. DESIGN ASPECTS OF DOUBLE HULL TANKERS 3 2.1 DEFINITION 3 2.2 NOMENCLATURE 3 2.3 CARGO TANK ARRANGEMENT 3 2.4 MATERIALS 4 2.5 ARRANGEMENT OF PRIMARY STRUCTURE BELOW 20,000 DWT 5 2.6 ARRANGEMENT OF PRIMARY STRUCTURE UP TO 150,000 DWT 5 2.7 ARRANGEMENT OF PRIMARY STRUCTURE ABOVE 150,000 DWT 6 2.8 AREAS REQUIRING SPECIAL ATTENTION 7 3. CRITICAL AREAS IN DOUBLE HULL TANKERS 19 3.1 GENERAL 19 3.2 STRESS CONCENTRATION LOCATIONS IN PRIMARY STRUCTURE 20 3.2.1 Smaller Tankers (Double Bottom and Double Hull) 20 3.2.2 Larger Double Hull Tankers (no longitudinal bulkheads) 20 3.2.3 Larger Double Hull Tankers (centreline longitudinal bulkhead) 21 3.2.4 Double Hull Tankers above 150,000 dwt (with longitudinal bulkheads) 22 3.3 MISALIGNMENT DURING CONSTRUCTION 23 3.4 CORROSION TRENDS 24 3.4.1 General 24 3.4.2 Cargo Tank 24 3.4.3 Double Hull Ballast Spaces 24 3.5 FATIGUE CONSIDERATIONS 25 3.6 AREAS IN DOUBLE HULL TANKERS REQUIRING SPECIAL ATTENTION 25 3.6.1 General 25 3.6.2 Cargo Tanks 25 3.6.3 Double Hull Ballast Spaces 26 4. EXPERIENCE ON STRUCTURAL DEFECTS IN DOUBLE HULLS 35 4.1 GENERAL 35 4.2 DEFECTS IN DOUBLE HULLS 35 WSIL 047 - Guidelines for the Inspection and Maintenance.indd iiiWSIL 047 - Guidelines for the Inspection and Maintenance.indd iii8/29/2008 12:52:02 PM8/29/2008 12:52:02 PM iv Page 5. CORROSION PROTECTION CONSIDERATIONS 37 5.1 GENERAL 37 5.2 LEGISLATIVE REQUIREMENTS FOR CORROSION PROTECTION 37 5.3 CHOICE OF CORROSION PROTECTION 38 5.3.1 Hard Coatings 38 5.3.2 Soft Coatings 38 5.3.3 Sacri? cial Anodes 39 5.3.4 Effectiveness of Corrosion Protection System 39 5.4 TYPICAL COATING SYSTEMS 39 5.4.1 Type of Paint 39 5.4.2 Water Ballast Tank Coatings 41 5.4.3 Cargo Tank Coatings 42 5.4.4 Main Deck Structure 42 5.5 QUALITY STANDARDS FOR COATING OF DOUBLE HULL SPACES 42 5.5.1 General Standards 42 5.5.2 Steelwork Preparation 43 5.5.3 Surface Preparation and Painting 44 5.5.4 Main Paint System Application 45 5.6 TYPICAL DEFECTS OF COATING SYSTEMS 45 5.6.1 Surface Cleanliness 45 5.6.2 Coating Integrity 46 5.6.3 Overcoating Intervals 47 5.6.4 Weather Effects on Coating 47 5.6.5 Other Failures 48 5.7 PLANNING, SUPERVISION AND GUARANTEES 49 5.7.1 Planning 49 5.7.2 Supervision 49 5.7.3 Guarantees 50 5.8 RECOMMENDATIONS FOR NEW CONSTRUCTION 50 WSIL 047 - Guidelines for the Inspection and Maintenance.indd ivWSIL 047 - Guidelines for the Inspection and Maintenance.indd iv8/29/2008 12:52:02 PM8/29/2008 12:52:02 PM v Page 6. DESIGN CONSIDERATIONS IN ACCESSIBILITY FOR INSPECTION AND MAINTENANCE 53 6.1 GENERAL 53 6.2 VISIBILITY REQUIREMENTS 53 6.3 ACCESSIBILITY REQUIREMENTS FOR DOUBLE HULL SPACES 53 6.3.1 Access from Weather Deck 53 6.3.2 Accessibility for Personnel Safety 54 6.4 ACCESS METHODS FOR INSPECTION 54 6.4.1 General 54 6.4.2 Access Methods for Inspection in Cargo Tanks 55 6.4.3 Access Methods for Inspection in Vertical Wing Spaces 56 6.4.4 Access Methods for Inspection in Double Bottom Spaces 56 6.5 VENTILATION AND INERTING REQUIREMENTS FOR DOUBLE HULL SPACES 56 6.5.1 General 56 6.5.2 Conventional Tank Ventilation Method 57 6.5.3 Ventilation by Ballast Pipe 57 6.5.4 Ventilation by Purge Pipe 57 6.5.5 Inerting by Ballast Pipe 57 6.5.6 Inerting by Deck Inert Gas Lines 57 7. SURVEY OF STRUCTURE 71 7.1 GENERAL 71 7.2 TYPES OF INSPECTION AND OBJECTIVES 71 7.2.1 Types of Inspection 71 7.2.2 Inspection Objectives 72 7.2.3 Inspection Phases 72 7.3 PLANNING AND PREPARATION FOR INSPECTION 72 7.3.1 Technical Information 72 7.3.2 Documentation Onboard 73 7.3.3 Risk Categories 73 7.3.4 Inspection Schedule and Venue 73 7.3.5 Inspection Personnel 73 7.4 EXECUTION OF SURVEY 73 7.4.1 General 73 7.4.2 Scope of Inspection 74 7.4.3 Communication 74 7.4.4 Safety Aspects 74 7.4.5 Data Collection 75 WSIL 047 - Guidelines for the Inspection and Maintenance.indd vWSIL 047 - Guidelines for the Inspection and Maintenance.indd v8/29/2008 12:52:02 PM8/29/2008 12:52:02 PM vi Page 7.5 REPORTING 75 7.5.1 General 75 7.5.2 Classi? cation Society’s Survey Report Forms 76 7.5.3 Owner’s Survey Report Forms 76 7.6 POST INSPECTION ANALYSIS OF SURVEY DATA 76 7.6.1 General 76 7.6.2 Steel Condition Assessment and Corrosion Trend Study 76 7.6.3 Coating Condition Assessment 77 7.6.4 Corrosion Protection System Assessment 77 7.6.5 Structural Integrity Analysis 77 7.6.6 Future Survey Requirement Analysis 77 8. MAINTENANCE AND REPAIR 79 8.1 GENERAL 79 8.2 TYPE OF REPAIR 79 8.3 MAINTENANCE AND REPAIR METHODS 79 8.3.1 Repairs of Existing Coated Areas in Segregated Ballast Tanks 80 8.3.2 Repairs of Uncoated Areas in Cargo Tanks 80 8.3.3 Pitting and Grooving Repair 81 8.3.4 Steel Renewal 81 8.3.5 Steel Reinforcement 81 8.3.6 Steel Design Modi? cation 81 8.3.7 Repairs of Structural Defects 82 8.4 OPTIMUM MAINTENANCE AND REPAIR STRATEGY 82 8.4.1 General 82 8.4.2 Short-Term Maintenance and Repair Programme 82 8.4.3 Long-Term Maintenance and Repair Programme 82 9. REFERENCES 85 APPENDIX 1 87 CATALOGUE OF STRUCTURAL DETAIL FAILURES IN DOUBLE HULL DESIGNS 87 WSIL 047 - Guidelines for the Inspection and Maintenance.indd viWSIL 047 - Guidelines for the Inspection and Maintenance.indd vi8/29/2008 12:52:02 PM8/29/2008 12:52:02 PM 53 Chapter 6 DESIGN CONSIDERATIONS IN ACCESSIBILITY FOR INSPECTION AND MAINTENANCE 6.1 GENERAL The International Association of Classi? cation Societies requires that means of access be provided to enable the Surveyor to perform the ‘overall’ survey of structures in a ‘safe and practical way’. However, for the enhanced ‘close-up’ survey of the structures, there are presently no speci? c Classi? cation Society requirements that specify the means of access by which this can be achieved for newbuildings. It has, therefore, become the Owner’s responsibility to work with the Classi? cation Society and the Shipyard, at the time of construction, to develop and incorporate proper means of access to enable ef? cient and effective future inspection and maintenance. IMO has recognized the importance of personnel safety in double hull spaces, and a new Regulation 12-2, “Access to Spaces in the Cargo Area of Oil Tanker”, has recently been incorporated into the 1974 SOLAS Convention. The double hull tanker includes both the large ‘open’ cargo spaces associated with traditional tankers and the ‘closed cellular’ water ballast tanks associated with other ship types. While well established means have been devised for large open cargo tanks, special attention needs to be given to the cellular water ballast tanks during the design stage, taking into consideration the knowledge of critical areas in tank structures, safety of personnel and tank ventilation. 6.2 VISIBILITY REQUIREMENTS Tank coatings of lighter colour should be considered for the double hull ballast tanks to provide improved visibility for the detection of corrosion, fractures and cargo oil leakage. 6.3 ACCESSIBILITY REQUIREMENTS FOR DOUBLE HULL SPACES Double hull tankers require safe and easy access to permit frequent and easy inspection of the ballast tanks to ensure that any structural fractures, coating failures and subsequent corrosion may be dealt with on a timely basis. 6.3.1 Access from Weather Deck Access to vertical wing and double bottom spaces of ballast tanks, cofferdams and other non-cargo spaces within the cargo tank area should be provided directly from the weather deck (Figs. 6.1 and 6.2). Every double bottom space should be provided with direct access, without passing through other neighbouring double bottom spaces (Fig. 6.3). Where the tanks are of con? ned or cellular construction, two separate means of access from the weather deck are recommended, one each at either end of the tank space. WSIL 047 - Guidelines for the Inspection and Maintenance.indd 53WSIL 047 - Guidelines for the Inspection and Maintenance.indd 538/29/2008 12:53:27 PM8/29/2008 12:53:27 PM 54 6.3.2 Accessibility for Personnel Safety A prime consideration should be the provision of adequate accessibility to allow for persons wearing breathing apparatus and to enable the removal of injured personnel being carried on a stretcher. One enlarged hatch of 600mm by 800mm minimum clearance, or larger, should be ? tted on the weather deck for rescuing injured personnel directly from the double bottom space via the vertical wing space. Alternatively, one of the deck access hatches can be enlarged and ? tted with a hinged top ladder with clear vertical straight access down to the tank bottom (Figs. 6.1 and 6.2). For rescue operation, at least one of the following type openings should be provided in each horizontal girder in vertical alignment within the vertical wing space: – 600mm by 800mm manhole or larger. – Rectangular shape of 600mm by 600mm with corner radius 100mm, or larger. – Circular shape of 670mm or larger. Gratings or safety guide rails should be ? tted for openings larger than 200mm diameter on bulkhead stringers and horizontal girders (Figs. 6.4 and 6.9). Step rungs and grip rails should be provided on inclined or curved surfaces to assist footing (Figs. 6.9 and 6.10). Two tier safety guide rails should be ? tted on the free edge of walkways, bulkhead stringers and horizontal girders (Figs. 6.4 and 6.5). Vertical access openings provided for each cellular space in double bottom or vertical wing spaces should have at least one enlarged manhole opening of 600mm by 800mm or larger, and the sills of these openings should not be more than 600mm above the standing surface or foothold. 6.4 ACCESS METHODS FOR INSPECTION 6.4.1 General The access methods for the inspection of tank structures are listed below:- (i) Permanent access arrangement such as:- (a) The ? tting of permanent staging. (b) The ? tting of bulkhead stringers as walkways. (c) The ? tting of horizontal girders as walkways. (d) The ? tting of independent horizontal walkways (Fig. 6.4). (e) The use of enlarged longitudinals as walkways (Figs. 6.4 and 6.5). (f) The ? tting of step rungs on faceplates of longitudinals for climbing (Fig. 6.6). WSIL 047 - Guidelines for the Inspection and Maintenance.indd 54WSIL 047 - Guidelines for the Inspection and Maintenance.indd 548/29/2008 12:53:27 PM8/29/2008 12:53:27 PM