Pipelines routed in parallel with overhead electric power transmission lines and/or AC-traction railways results in induced AC-voltages on pipelines that may cause corrosion sometimes with penetration rates in excess of 10 mm/yr despite properly imposed cathodic protection. Due to the increasing demand from pipeline operators a concept for AC corrosion detection has been presented which is based on an instrumented coupon device with capabilities of logging corrosion condition as well as electrical fingerprints on the coupon buried in the ground along the pipeline and electrically connected hereto.

Through field trial examples, it has been shown that the AC corrosion mechanisms involve alkalization of the environment nearby the coating defect, and in combination with AC, corrosion may be induced. Therefore low levels of cathodic protection are preferred over high levels of cathodic protection (as long as standard CP requirements are met) since the direct current (DC) provides alkalization. The presented concept for AC corrosion detection clearly monitored such behavior.

Subject
Electric current, Voltage, Cathodic protection, Corrosion rate, Pipelines, Instrumentation, Alternating current corrosion, Risk management, Coating defects, Corrosion resistance, Corrosion coupons, Elements, Soil
Keywords:
AC corrosion monitoring, AC corrosion mechanisms, On-line technique
© 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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