This paper describes a research program conducted to determine the factors controlling stress corrosion cracking of A516 Grade 70 steel in monoethanolamine (MEA) and diethanolamine (DEA) solutions used to remove acid gases from natural gases. Polarization curves were generated and slow-strain-rate tests were conducted in MEA and DEA solutions simulating compositions of amine solutions used in natural gas treatment plants. It was found that A516 Grade 70 steel is susceptible to SCC in both MEA and DEA solutions. SCC susceptibility at anodic potentials in solutions of both amines resulted from the presence of CO2. Cracking did not occur in pure amine solutions at active-passive transition potentials, while severe SCC occurred at or near active-passive transition potentials in both MEA and DEA solutions in which CO2 was the only acid gas present. H2S in small concentrations prevented cracking of A516 steel in MEA and DEA solutions containing CO2. The role of CO2 appears to be to increase anodic current density at the active-passive transition potential to the extent that SCC by a film-rupture mechanism becomes possible. Addition of small amounts of H2S to CO2-containing MEA and DEA solutions alters anodic dissolution kinetics and completely suppresses active-passive behavior, thereby preventing cracking by a film-rupture mechanism from occurring.

Subject
Materials, Anode potential, Cathodic potential, Hydrogen evolution, Free corrosion potential, Density, Natural gas, Solutions, Amines, Anodic current, Steel, Cracking, Stress corrosion cracking
© 1988 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).
1988
Association for Materials Protection and Performance (AMPP)
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