Guidance Manual for the Inspection and Condition Assessment of Tanker Structures Tanker Structure Co-operative Forum Witherby Seamanship International Ltd 4 Dunlop Square, Livingston, Edinburgh, EH54 8SB, Scotland, UK Published in 1986 Reprinted 1987 ” 1989 ” 1990 ” 1991 ” 1992 ” 1994 ” 2000 ” 2002 ” 2004 ” 2006 ” 2007 ” 2009 ISBN 13: 978 0 948691 11 9 ISBN 10: 0 948691 11 5 © Copyright is held by Witherby Seamanship International Ltd. on behalf of The Tanker Structure Co-operative Forum 1986 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Printed & bound in Great Britain by Bell & Bain Ltd. Glasgow Published in 2009 by Witherby Seamanship International Ltd 4 Dunlop Square, Livingston, Edinburgh, EH54 8SB, Scotland, UK Tel No: +44(0)1506 463 227 Fax No: +44(0)1506 468 999 Email: info@emailws.com www.witherbyseamanship.com Notice of Terms of Use While the advice given in this guide has been developed using the best information currently available, it is intended purely as guidance to be used at the users’ own risk. No responsibility is accepted by the International Chamber of Shipping, the Oil Companies’ International Marine Forum, the Tanker Structure Co-operative Forum, or by any person, ?rm, corporation or organisation who or which has been in any way concerned with the furnishing of information or data, the compilation, publication or authorised translation, supply or sale of this guide, for the accuracy of any information or advice given herein or for any omission herefrom or for any consequences whatsoever resulting directly or indirectly from compliance with or adoption of guidance contained herein even if caused by a failure to exercise reasonable care. III Introduction This manual attempts to combine in one document the various sources of information necessary for assessing the condition of ballast and cargo tank structure of tankers in service. The manual is based on the experience and practices of members of the Tanker Structure Cooperative Forum* consisting of Owners, Operators and Classi?cation Societies. The following organisations were members of the Tanker Structure Co-operative Forum at the time of compiling this manual:— American Bureau of Shipping Andreas Ugland and Sons A/S BP Shipping Bureau Veritas Chevron Shipping Det Norske Veritas Exxon International Company Lloyd’s Register of Shipping Maritime Overseas Corporation Mobil Shipping and Transportation Sanko Steamship Company Shell International Marine Guidance is given ?rst on survey preparation including a review of requirements, safety aspects, equipment, and details of carrying out and reporting differing types of surveys. The analysis of data follows with the interpretation of wastage and structural defects in terms of the effects on local strength or overall structural integrity. The manual incorporates, where appropriate, the results of Forum activities in areas of corrosion, defects and repairs, ultrasonic gauging and the strength of corroded structural items. The manual is not intended to set down standards, and in some cases the practices of individual members of the Forum differ on speci?c aspects, but it gives guidelines in a form which can be adapted appropriately to the particular uses of individual organisations. *Appendix I contains the background to the Forum activities. V Contents Page No. INTRODUCTION V 1. SURVEY PREPARATION GUIDELINES 1 1.1 SURVEY REQUIREMENTS 1 1.1.1 Class and Statutory Requirements 11.1.2 Owner’s Requirements 2 1.2 SAFETY AND ACCESS 3 1.2.1 Safety During Surveys 3 1.2.2 Access to the Structure 7 – Permanent Arrangements 7 – Temporary Staging 7 – Mobile Platforms 7 – Rafting 7 – Remotely Operated Devices 8 – Use of Divers 8 – Other Devices 8 1.3 ULTRASONIC THICKNESS DETERMINATION 9 1.3.1 Survey Team Quali?cations 9 1.3.2 Basic Equipment Types 9 1.3.3 Thickness Measurement Accuracy 11 1.3.4 Measurement Procedures 11 1.4 TECHNICAL BACKGROUND FOR SURVEYS 12 1.4.1 Nomenclature 12 1.4.2 Structural Defects 14 1.4.3 Corrosion Aspects 14 – Typical Corrosion Patterns 14 – Factors Contributing to Corrosion 15 1.4.4 Corrosion Control systems 17 2 SURVEY EXECUTION GUIDELINES 19 2.1 GENERAL PLANNING REQUIREMENTS 19 2.2 CLASSIFICATION SOCIETY SPECIAL SURVEY/IACS UNIFIED REQUIREMENTS 19 2.3 GENERAL CONDITION SURVEY 20 2.4 DETAILED CONDITION SURVEY 22 2.5 CORROSION RATE SURVEY 23 2.6 REPAIR SPECIFICATION SURVEY 23 VI Page No. 3. SURVEY DATA ANALYSIS GUIDELINES 25 METHOD OF ASSESSMENT 253.1 STRUCTURAL INTEGRITY 253.2 ACCEPTANCE CRITERIA 263.3 REPAIR METHODS 293.4 General Corrosion 293.4.1 Local Phenomena 293.4.2 BIBLIOGRAPHY 31 APPENDIX I Background to Forum Activities 33 APPENDIX II International Association of Classi?cation Societies: Uni?ed Requirements for the Special Hull Surveys of Oil Tankers 35 APPENDIX III International Safety Guide for Oil Tankers and Terminals: Extract, Chapter 10 – ‘Entry into and Work in Enclosed Spaces’ 41 APPENDIX IV Catalogue of Structural Detail Failures 51 APPENDIX V Forms and Procedures for Data Collection and Reporting 147 135 TYPICAL DAMAGEPROPOSED REPAIR TANKER STRUCTURE CO-OPERATIVE FORUM SUBJECT: CATALOGUE OF STRUCTURAL DETAILS FIGURE 77 FIGURE 77 FACTORS CONTRIBUTING TO DAMAGE 1. Corrosion losses (aided by ?ume/swash action) causing thinning and knife-edging of plating surrounding openings. 2. Stress concentration at openings placed too close together. 3. Flexing of structure due to ?ume/swash action. 4. Lack of suitable stiffening around openings. 5. Inadequate shear strength and stiffness in the bulkhead. GROUP No. 12 LOCATION: Lightening holes and openings in primary webs and swash Bulkheads EXAMPLE No. 4: Fractures of longitudinal ?ume/swash bulkhead plating at openings 136 TYPICAL DAMAGEPROPOSED REPAIR TANKER STRUCTURE CO-OPERATIVE FORUM SUBJECT: CATALOGUE OF STRUCTURAL DETAILS FIGURE 78 FIGURE 78 FACTORS CONTRIBUTING TO DAMAGE 1. Overall shear distortion of bulkhead. 2. Stress concentration at corner of opening. 3. Corrosion losses due to ?ume action. GROUP No. 12 LOCATION: Lightening holes and openings in primary webs and swash bulkheads EXAMPLE No. 5: Fracture at corner of ?ume in longitudinal bulkhead 137 TANKER STRUCTURE CO-OPERATIVE FORUM SUBJECT: CATALOGUE OF STRUCTURAL DETAILS FIGURE 79 FIGURE 79 1. REPAIR NOTES 1.1 In general, plating in way of fractures should be cropped and renewed. | However, when the fractures are judged to be of a minor nature, gouging, welding and ?tting of a doubler ring is acceptable (see Examples Nos. 2 and 4). 1.2 At the large opening (see Example No. 5) the opportunity should be taken to increase the radius at the corners to reduce the stress concentration. Care should be taken to ensure that any weld butts in inserts do not occur within a radius corner. 1.3 Where doubler rings are ?tted, any knife-edging around the opening should be cropped, and the doubler ring sized to ?t the larger opening. The inner radius” of the ring should be 10 mm larger than the radius of the opening to allow a proper ?llet weld. 1.4 Where the openings in the structure are not essential for drainage, access, passage or ?ume performance, they should be plated over (see Examples Nos. 1 and 3). Depending on the arrangement and location, additional stiffening may be required. 1.5 Particular attention should be paid to the quality of welding especially at return of welds. 1.6 For recurrent fractures, notch tough steel should be considered. 1.7 Protective coatings in way of repairs should be restored. 1.8 Structure as shown in Examples Nos. 1 to 4 were encountered on older vessels (15 years plus), and are generally not used in present practice. Fracturing was quite common especially when corrosion losses affected the material in way of openings. 2. ALTERNATIVE REPAIRS 2.1 Instead of doubler rings, the holes can be plated over or new plating can be ?tted in way of multiple openings such as those in Examples Nos. 1, 2 and 4. Increased thickness of plating, notch tough steel and/or additional stiffening should be considered to prevent re-occurrence of the cracking. 3. UNSUCCESSFUL REPAIRS 3.1 Simple gouging and rewelding of fractures will lead to re-occurrence of the fractures. 3.2 For Example No. 5, repairs utilising smaller sized insert plates resulting in butts within the radius. corner were not successful, and resulted in fractures along the weld of the insert plate and into existing plating. ADDITIONAL NOTES GROUP No. 12 LOCATION: Lightening holes and openings in primary webs and swash bulkheads EXAMPLE NO.: 1 THROUGH 5