The energy transportation network of the United States consists of over 2.5 million miles of buried pipelines. It is of prime importance the integrity of the metallic assets due to degradation in soil conditions because of their constant exposure to the aggressive, dynamic, and heterogeneous environment. This degradation process, involves a sequence of process starting with the coating damages/failures and the following electrochemical reactions. External corrosion can result in gradual and usually localized metal loss on the exterior surface of failure coating, resulting in reduction of the wall thickness of the metallic asset. Indirect technologies, such as DC basis have been able to detect and pinpoint two conditions in the pipeline, intact and holiday (active surface or coating anomaly) with good confidence. In this work we consider different levels of corrosion surface severity when a coating holiday (anomaly) exists. Different X52 metallic samples were characterized by using DC polarization and AC impedance to distinguish the differences in terms of capacitive and surface corrosion severity when the metallic samples get a coating failure. Two different coatings were used to characterize different activity surface conditions when there is a coating holiday. The performed set of laboratory experiments include the effects of the applied cathodic protection potential and the metallic surface condition in the presence of holidays (specifically active and passive state) under cathodic protection and simulated soil conditions. Functional correlations and plot results could be found with the fundamentals of electrochemistry and electrical signals by following the DC polarization, relaxation plots and Electrochemical Impedance Spectroscopy results performed in the laboratory. In light of the differences between each surface condition founded experimentally we are able to screen and distinguish the severity conditions of the surface under anomaly coating conditions and potential detection methods/tools for potential pipeline inspection practices.

Subject
Holidays, Steel surfaces, Cathodic protection, Cathodic potential, Fusion bonded epoxy coating, Metallic surfaces, Coal tar, Pitting, Coating defects, Surface profile, Instant off potential, Electrochemical potential, Soil
Keywords:
external corrosion, severity detection, potential decay, impedance properties, electrochemical characterization
© 2022 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).
2022
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.