Previous research has suggested that a coated steel substrate can be cathodic to boldly exposed steel in seawater. As a result logic would suggest that the corrosion rate at defects in the coating would be a function of the coating to holiday surface area ratio. To examine this hypothesis four (4) surface area ratios were tested in natural seawater. These ratios are 3:1, 10:1, 136:1 and 1176:1 (coated to exposed steel). Coated panels were painted with a MIL-P-24441 epoxy barrier coating and electrically coupled to exposed steel. During testing the current between coated and uncoated samples was monitored along with the potential between the couple and a saturated calomel reference electrode (SCE). Testing has been conducted for over one year, with each area ratio showing interesting trends.

This paper discusses the current flow of each area ratio, and how it relates to the corrosion rate of exposed steel. Whether the corrosion is anodically or cathodically controlled, and to what extent, are evaluated. Finally, “real-world” applications of this type of analysis will be discussed.

Subject
Holidays, Coated steel, Test methods, Steel surfaces, Coatings, Corrosion currents, Corrosion rate, Steel coupons, Current densities, Steel, Polarization, Polarization resistance, Corrosion potential
© 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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