This study evaluated the technical feasibility of applying a combination of calcareous deposit coating and cathodic protection (anodes) in lieu of completely coating ship ballast tanks with high-performance coatings (epoxy). As an initial step to achieve this goal, batches of calcareous deposits were formed on A36 grade carbon steel plates, induced by cathodic polarization (CP) in natural seawater. The effect of deposition parameters such as CP current density, potential, and coating time on the coating's characteristics were evaluated to establish the optimum coating condition. Results showed that good overall calcareous coating can be achieved by lowering the current density as much as possible in the range 0.1-0.5mA/cm2 and by increasing coating formation time.

Optimum number and arrangement of CP anodes for calcareous coating of a 3-dimensional structure such as a ballast tank were also evaluated by using Finite Element Method (FEM) analysis of potential distribution under CP. The results were fairly consistent with the experimental data obtained from coating tests made on the inner surface of a box-type, mock-up structure.

Subject
Steel structures, Ballast, Zinc rich coatings, Immersion tests, Coatings, Finite element analysis, Anode surfaces, Seawater, Epoxy coatings, Current densities, Marine vessels, Calcareous deposits, Anodes
Keywords:
calcareous deposits, cathodic protection, marine corrosion, ship ballast tank, FEM analysis
© 1999 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1999
Association for Materials Protection and Performance (AMPP)
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