Abstract
Carbon steel specimens have been exposed in CO2 containing brine with different amounts of H2S at 70 and 80 °C. Addition of 0.02 mMol/l sulphide, corresponding to 45 Pa (0.0065 psi) H2S partial pressure, to brine with 70 kPa (10 psi) CO2 at pH 4.2 caused a rapid formation of a protective corrosion film. After about 15 minutes the anodic dissolution rate at a given potential was reduced two decades. The rate of the cathodic reactions was only slightly reduced. These changes in the electrochemical kinetics increased the corrosion potential to a region where localised breakdown of the protective film and pitting corrosion could take place.
After a day's exposure, H2S partial pressures in the range 14 Pa (0.002 psi) to 56 Pa (0.0081 psi) led to corrosion rates varying unsystematically between 0.2 mm/year to 3 mm/year. A pronounced decrease of the corrosion rate was frequently observed for low H2S contents. An H2S partial pressure of 56 Pa (0.0081 psi) resulted consistently in an increase of the corrosion rate. For H2S partial pressures between 15 and 60 Pa (0.0022 and 0.0087 psi) and a CO2 partial pressure of 56 kPa (8.1 psi), the following relationship between corrosion rate and pH was observed:
(1)
© 1994 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).
1994
Association for Materials Protection and Performance (AMPP)
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