Degradation of painted steel, aluminium and zinc exposed to air saturated sea water have been studied by using dc electrochemical methods and by visual examination of long term exposed specimens. The dc measurements were performed on surfaces with a continuous paint film while the long term specimens were polarized by a defect in the paint film.

The dc measurements of coated aluminium, steel and zinc have been found to give information about the mechanism of corrosion. The results illustrate the importance of both the properties of the metal substrate and the paint film. Coated steel galvanically coupled to bare steel was found to have a high potential, and hence to act as a cathode versus bare steel. For coated aluminium, however, initiation of corrosion at the metal/coating interface was found to take place. The behaviour of coated zinc was found to be similar to that of coated steel, but also different. The potential was high compared to bare zinc, which means that coated zinc acts as cathode. However, the potential of coated zinc also suggests some initiation of corrosion at the zinc/coating interface.

The results from the long term exposure test are in accordance with the results from the short term tests.

Subject
Films, Coated steel, Steel surfaces, Water, Aluminum, Corrosion initiation, Epoxy coatings, Electrical resistivity, Steel, Corrosion resistance, Zinc, Galvanic current, Paints
Keywords:
organic coating, paint, test method, electrochemical method, immerson test
© 1990 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).
1990
Association for Materials Protection and Performance (AMPP)
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