Two coating systems were examined based on fundamental principles for their barrier properties in relation to corrosion under a blistered coating and under a crevice coating – a delaminated coating with a holiday. In a blister or in a crevice but away from the holiday, where cathodic protection (CP) could be ineffective, the corrosion rate could be determined by the coating barrier properties and increases as the coating deteriorates. It was found that in a crevice the pipeline surface could be better protected if the soil is more conductive because then CP can penetrate deeper into the crevice. For more resistive soils, a higher CP potential is needed in order for protecting the disbonded area away from the holiday. This may however require higher cost and result in perhaps hydrogen induced cracking (HIC), a brittle failure of the pipelines due to atomic hydrogen ingression into the metal substrate. When the coating adhesion is lost, good barrier properties for a blistered coating and good barrier properties and an effective CP for a crevice coating are the ways to provide control of the pipeline corrosion.

Subject
Holidays, Pipe surfaces, Barriers, Coatings, Corrosion rate, Pipelines, Soil resistivity, Fusion bonded epoxy coating, Permeation, Crevices, Crevice corrosion, Barrier coatings, Soil
Keywords:
pipeline, coating, cathodic protection, corrosion, crevice, permeation
© 2005 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).
2005
Association for Materials Protection and Performance (AMPP)
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