Evidence from laboratory experiments and field observations on near-neutral pH SCC of pipeline steel is reviewed. Emphasis is placed on the effects of environmental parameters, such as potential, pH and HCO3−/CO32− concentration, on the SCC mechanism. The results are interpreted in terms of either a dissolution-based or hydrogen-based mechanism.

The weight of evidence supports a hydrogen-based mechanism for near-neutral pH SCC. Dissolution may play a role in SCC initiation. Enhanced rates of hydrogen evolution and permeation appear possible under near-neutral pH SCC conditions, whilst the observed dissolution rates and the absence of an efficient mass-transport mechanism to support rapid crack-tip dissolution seem to rule out dissolution as an important contributor to crack growth.

Subject
Environmental cracking, Hydrogen permeation, Corrosion rate, Cathodic potential, Dissolution, Corrosion cracking, Stress cracking, Acidity, Oxide surfaces, Steel, Cracks, Electrode potential, Hydrogen
Keywords:
pipeline steel, near-neutral pH SCC, hydrogen mechanism, dissolution mechanism, crack chemistry, corrosion rate, hydrogen permeation, hollow tensile specimen, initiation, propagation
© 2000 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).
2000
Association for Materials Protection and Performance (AMPP)
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