This paper describes the principles, operation, and testing of an Airborne Cathodic Monitoring System (ACMS)(1) that detects upset conditions on pipelines protected by impressed current. ACMS consists of a battery of highly sensitive and highly filtered magnetic field coils, installed on a helicopter or light airplane, that continuously measure the magnetic field generated by the ripple from an alternating current source. Measurement of the magnetic field leads to a direct determination of current along the pipeline. Upset conditions on the cathodic protection system and the pipeline can be deduced by analysis of the rate-of-change of current. Combined with ground measurements of voltages and currents at adjacent rectifiers and at sample test points along the pipeline, ACMS data can accurately determine voltage and amperage values at any point between adjacent rectifiers. Up to 200 miles of pipeline can be surveyed in one day with ACMS---at about half the cost of an equivalent close-interval survey. An ancillary desktop computer program can be used to rapidly detect changes to the cathodic system and the pipeline between surveys. On 6 November 1991, the Office of Pipeline Safety, Department of Transport, officially recognized ACMS as an acceptable method of pipeline inspection and monitoring1.

Subject
Electric current, Sensors, Piping, Voltage, Cathodic protection, Tape, Slopes, Pipelines, Inspection, Rectifiers, Cathodic protection survey, Surveys, Upset
Keywords:
cathodic systems inspection, airborne magnetometry, upset conditions on pipelines, remote pipeline inspection
© 1992 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).
1992
Association for Materials Protection and Performance (AMPP)
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