Potential-pH equilibrium diagrams (Pourbaix diagrams) for the systems Fe-Cr-Cl--H2O and Fe-Cr-S-H2O at 25°C are presented. The mixed oxide FeCr2O4 and the various iron sulphides are considered. The data were selected to provide some consistency between data from different sources. The diagrams are presented for a chloride concentration that corresponds to seawater and for a sulphide concentration of 0.001 mol/kg H2S (approximately pH2S = 0.01 bar).

The diagrams show the intricate stability regions of iron sulphides, chromium oxide or mixed Fe-Cr oxide and dissolved species within a rather narrow range of potential and acid pH.

Some observed facts are reported that illustrate the interest of the diagrams to interprete and predict phenomena. Interesting progress on testing procedures and on mechanisms of localised corrosion could be gained by future work.

Subject
Hydrogen sulfide, Stability, Water, Materials, Thermodynamics, Oxide formation, Iron sulfides, Pourbaix diagrams, Acidity, Chromium oxide, Sulfides, Localized corrosion, Stainless steel
Keywords:
thermodynamics, Pourbaix diagram, 13Cr stainless steel, H2S media
© 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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