Sulfuric acid has been found to induce stress corrosion cracking (SCC) in zirconium (UNS R60702). Laboratory studies indicate SCC can develop in a sulfuric acid concentration range of approximately 64 to 69 percent. Mechanistically, it is proposed that SCC initiates at local defects in the zirconium oxide film when the rate of reformation of the oxide film (repassivation) is approximately equal to the rate of oxide film breakdown (rate at which unfilmed zirconium surfaces are generated). Laboratory data indicates that zirconium oxide film breakdown may occur by two paths: (1) mechanical, for example, by plastic deformation or (2) electrochemical, for example, by exposure to sulfuric acid containing ferric and possibly other oxidizing ions.

Three approaches to prevent SCC of zirconium in sulfuric acid have been demonstrated in laboratory tests: (1) heat treatment for stress reduction, (2) shot peening to induce residual compressive stresses and (3) addition of a hydrocarbon, in this case isopropyl alcohol, to the sulfuric acid.

Subject
Acids, Corrosion failures, Ions, Sulfuric acid, Zirconium, Oxide films, Stress cracking, Stress, U bends, Caustic stress corrosion cracking, Stress corrosion cracking, Residual stress, Slow strain rate technique
Keywords:
zirconium, sulfuric acid, stress corrosion cracking, SCC
© 1992 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).
1992
Association for Materials Protection and Performance (AMPP)
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