An experimental study has been conducted with buried coupons to simulate holidays on a coated pipe. That study has shown that the instant-off potential (the pipe-to-soil potential when all of the current is stopped) will indicate approximately the true polarized potential of the largest holiday. When the holidays are freely exposed to the soil, this potential will be the least negative true polarized potential of all of the holidays sensed; smaller holidays will have more negative true polarized potentials. Experiments have shown that the most negatively polarized a holiday can become is about -1.15 volts (Cu/CuSO4). If holidays (or crevices or areas under disbonded coating) are shielded from the cathodic-protection currents, they may have true polarized potentials less negative than the largest holiday, but will go undetected in the apparent instant-off potential. A mathematical model shows that the relative resistance path between the reference electrode at ground level and the holidays is a controlling parameter in the relation between the true polarized potential for a given holiday and the value of the apparent instant-off potential for all holidays.

Subject
Holidays, Electric current, Pipe to soil potential, Steel coupons, Reference electrodes, Pipelines, Negative potentials, Steel, Polarized potential, Instant off potential, Soil, Electrode potential, Coupons
© 1983 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).
1983
Association for Materials Protection and Performance (AMPP)
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