A theoretical and experimental study of potential gradients in crevices between a piece of steel and an insulating coating has revealed that the condition of the steel surface and the potential of the steel at the coating holiday have important effects on the potential gradient. Holiday potentials more negative than that required to form hydrogen bubbles can cause difficulty in controlling the potential under disbonded coatings, whereas good control of potential under the coating appears to be possible at less negative holiday potentials. Thus, it appears that it should be possible to achieve cathodic protection under disbonded coatings in many cases. The potential gradients are surprisingly insensitive to the shape and thickness of the crevice. A relatively simple mathematical relationship exists among the potential gradient, the current flowing in the electrolyte under the coating, and the current density on the metal.

Subject
Holidays, Electric current, Steel surfaces, Coatings, Piping, Pipelines, Crevices, Negative potentials, Experimental data, Bubbling, Steel, Protection potential, Electrochemical potential
© 1982 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).
1982
Association for Materials Protection and Performance (AMPP)
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