All the theoretical predictions described in Part I of this study, based on the new mechanisms for hydrogen charging and hydrogen stress cracking or on the resulting new model for permeation, have been effectively confirmed:

  • For hydrogen charging, they explain why the severity of the medium does not depend in the same way on PH2S for phenomena involving either “internal” or “external” hydrogen.

  • For hydrogen stress cracking (HSC), a stress applied at a surface not exposed to wet H2S is ineffective.

  • In the case of permeation, the difference between “thin” and “thick” membrane behavior had already been reported in the literature, even though the thin membrane results were considered as artefacts, due to the lack of a suitable interpretative model. With the new model, all these "anomalies" can be perfectly explained, including the sensitivity of the measured diffusion coefficients to membrane thickness and cathodic current, and the absence of real signification of the permeation peaks.

These three types of verification thus provide very strong additional support for the mechanisms described in Part I. They emphasize the need to focus future permeation studies on thin membranes, which are the only type representative of HSC, and to perform materials selection testing in conditions more representative of the damage phenomena to be avoided.

Subject
Hydrogen sulfide, Steel surfaces, Materials, Fluxes, Hydrogen concentration, Degassing, Diffusion, Cathodic current, Iron, Permeation, Stress, Sulfide stress cracking, Hydrogen
Keywords:
steel, hydrogen charging, internal hydrogen, external hydrogen, hydrogen stress cracking, H2S, sulfide stress cracking, permeation
© 2001 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).
2001
Association for Materials Protection and Performance (AMPP)
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