This paper presents the results of a four year laboratory program to determine the correlation between the potential of a pipeline coating defect and a catholic protection (CP) coupon buried in the same environment. The factors evaluated include exposed steel area, geometry, distance from CP anodes, and temperature.

Buried pipelines and electrically bonded CP coupons experience similar effects from CP systems and interference currents (e.g. Telluric and stray). When it is impradical to correct for voltage drops in pipeline potential measurements by disconnecting al current sources, CP coupons may be used to ensure that adequate cathodic protection has been achieved. Disconnecting coupons from the pipe removes IR-drop and mixed potential* errors from coupon potential measurements.

This testing was designed for application to the Trans Alaska Pipeline. Site specific engineering evaluations are recommended for application of these results to other pipelines.

Subject
Electric current, CP coupons, Water, Piping, Pipelines, Defects, Coating defects, Polarization, Instant off potential, Polarization resistance, Soil, Anodes, Coupons
Keywords:
cathodic protection, coupon, Telluric current, stray current, interference, IR-drop, monitoring, pipeline
© 1997 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).
1997
Association for Materials Protection and Performance (AMPP)
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