On rare occasions, field experience has shown that the corrosion rate from exposure to CO2 can vary greatly among different grades of carbon and alloy steels. The literature attributes the variation in corrosion rate to the microstructure resulting from heat treatment. A normalized plain carbon steel with a pearlitic microstructure is far superior to a hardened and tempered alloy steel with a martensitic microstructure. This paper presents two case histories from oil wells in the Middle East, wherein hardened and tempered alloy steel gas lift equipment underwent severe corrosion from CO2. In one case, the API J-55 tubing string experienced no corrosion. This has prompted consideration of the use of normalized steel for completion equipment in order to achieve corrosion performance similar to the J-55 tubing. For the equipment used in these wells, it was determined that alloy steel cannot provide a pearlitic microstructure while still maintaining good metallurgical properties. This study concluded that 9Cr-1Mo stainless steel has superior corrosion resistance and is recommended for completion equipment in these types of environments.

Subject
Microstructure, Iron sulfides, Corrosion scales, Tubing, Pearlite, Steel, Equipment, Pitting, Corrosion resistance, Normalizing, Heat treatment, Alloy steel, Martensite
Keywords:
carbon dioxide corrosion, mesa attack, pitting, pearlite, martensite, microstructure, J-55, N-80, 9Cr-1Mo, tubing
© 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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