Expanding the basic knowledge required for improved understanding of hydrogen sulfide (H2S) corrosion of mild steel is needed. When it comes to even the most basic chemical descriptors of aqueous H2S systems such as: H2S solubility, water chemistry, polymorphism of iron sulfide, the formation or dissolution of iron sulfide scale, and its protectiveness, many open questions persist and more investigation is required. Inconsistencies in prevailing expressions for H2S solubility constant (KH2S), the first dissociation constant (Ka,1) and the second dissociation constant (Ka,2) were reviewed here. By comparing with experimental data, the best prediction model for H2S solubility and dissociation in an H2S-H2O system was identified. Occurrence of iron sulfide polymorphs was experimentally investigated and it was found that, in short term exposures, mackinawite formed at 25°C, while greigite and pyrite were detected at 60°C. The solubility limits for these iron sulfides were determined. Simplified Pourbaix diagrams for the H2S-H2O-Fe system have been constructed with different meta-stable and stable iron sulfides (mackinawite, pyrrhotite, greigite and pyrite) to predict the corrosion products in H2S corrosion of mild steel.

Subject
X-ray diffraction, Mackinawite, Thermodynamics, Precipitates, Iron sulfides, Electrochemical reactions, Pourbaix diagrams, Pyrrhotite, Troilite, Corrosion products, Constants, Pyrite, Steel
Keywords:
Hydrogen sulfide, polymorphous iron sulfide, Pourbaix diagram, solubility constant, dissociation constant, solubility limit
© 2013 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).
2013
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.