Some underground pipeline coatings, such as asphalt enamel, coal tar and fusion-bonded epoxy, are said to be CP-compatible. When these coatings degrade and groundwater contacts the pipe, the surface is still protected from corrosion and stress corrosion cracking (SCC) as the CP current can pass through the permeable coating. However, the electrochemical reactions on the pipe surface generate a local environment under the coating quite different from that in the surrounding soil. If CP is lost, the environment under the coating will change over time. As the local environment evolves it could lead to an environment susceptible to SCC and/or corrosion.

A mathematical model has been developed to predict the generation and evolution of the environment under a disbonded permeable coating as a consequence of the action of CP. The model couples the electrochemical reactions on the surface of the pipe to the transport of species to and from the pipe surface through the permeable coating and the surrounding soil. The model is structured to use available field data (such as soil and groundwater data and information from CP surveys) to predict conditions on the pipe surface.

Subject
Pipe surfaces, Water, Coatings, Precipitation (solids), Asphalt, Fusion bonded epoxy coating, Acidity, Porosity, Pores, Mathematical models, Chemical reactions, Soil, Stress corrosion cracking
Keywords:
Pipeline, coating, permeable, shielding, CP-compatible, cathodic protection, corrosion, high-pH SCC, low-pH SCC, mathematical model
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.