MICROBIALLY-INFLUENCED CORROSION IN DOUBLE-HULL TANKERS A SCOPING PAPER

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1 MICROBIALLY-INFLUENCED CORROSION IN DOUBLE-HULL TANKERS A SCOPING PAPER

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3 INSTITUTE OF PETROLEUM MICROBIALLY-INFLUENCED CORROSION IN DOUBLE-HULL TANKERS A SCOPING PAPER March 2001 Published by The Institute of Petroleum, London A charitable company limited by guarantee

4 Copyright 2001 by The Institute of Petroleum, London: A charitable company limited by guarantee. Registered No , England All rights reserved No part of this book may be reproduced by any means, or transmitted or translated into a machine language without the written permission of the publisher. ISBN Published by The Institute of Petroleum Further copies can be obtained from Portland Press Ltd. Commerce Way, Whitehall Industrial Estate, Colchester CO2 8HP, UK. Tel: 44 (0) sales@portlandpress.com

5 CONTENTS Acknowledgements... vii 1 Summary Introduction The sulphur cycle Sulphide generation Sulphur and sulphuric acid generation Sources of contaminating microbes Oilfield Tankers Crude oil types Toxic components and biodegradability Mechanisms of microbial corrosion General Different steel grades and qualities with respect to corrosion Effect of temperature on corrosion rates Possible treatment and prevention strategies Repair of pits Coatings Biocides Corrosion inhibitors Past and current activities Tankers used as floating production storage and offloading units at offshore oilfields Ballast water Suggestions for future work Conclusions References Page v

6 ACKNOWLEDGEMENTS Author Dr Barry Herbert, Chairman of the Institute of Petroleum s Upstream Microbiology Committee. The author would like to thank Jim Stott of CAPCIS and Graham Hill of ECHA for invaluable information and reviewing this document. He would also like to thank Bjarne Thygesen of INTERTANKO for cooperation and providing information on the operation of the cargo tanks in VLCCs. Finally, thanks are due to Martin Maeso of the IP for support and reviewing the document. The Institute of Petroleum and the individual members of its Committees, cannot accept any responsibility of whatsoever kind, for damage or alleged damage or harm arising or otherwise occurring from the application of this report. vi

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8 1 SUMMARY One of the consequences of the Exxon Valdez oil spill in Alaska has been the requirement that all oil tankers built today are required to have double hulls. Whilst this has the obvious potential to reduce the likelihood of a catastrophic spill, there is a view that it has resulted in increased corrosion within the crude oil cargo tanks of these vessels when compared with their single hull counterparts. The underlying cause of the increased corrosion incidents has been identified in many cases as being due to microbial activity. Both pitting corrosion of the tank bottoms by sulphate reducing bacteria and corrosion of the undersides of the deck plates by sulphur oxidising bacteria have been identified. This scoping paper reviews the available published information on the operation and corrosion of the storage tanks in tankers and extends the findings to floating production storage and offloading units (FPSOs). There is a considerable amount of information and experience on microbially-influenced corrosion (MIC) in the literature (most notably that pertaining to oilfield operations) that helps in gaining a better understanding of what are the most probable causes (and possible means of prevention) of the perceived enhanced MIC in double hull tankers. Two main causes for the increased corrosion have been suggested steel quality and higher operating temperatures in the cargo tanks. Both of these claims are examined. A number of investigations have been conducted by various organisations over recent years and some are still ongoing most notably in Japan. A number of organisations have issued guidelines (OCIMF, TSCF, ABS, and INTERTANKO) to their members on how to avoid and mitigate corrosion problems. However, there is little published information on the possible mechanisms in-situ influencing microbial activity. This scoping paper aims to summarise what information is available and to provide a critique on whether the data support the various theories on MIC in double hull tankers. It also aims to identify areas where further study would be beneficial. 1