Failures of Inconel-600 steam generator tubes by caustic induced stress corrosion cracking have occurred in pressurized water reactors around the world.1,2  These failures have occurred in plants which used coordinated phosphate control of the secondary chemistry,3  in those which used an all volatile treatment,4  and in those which were in transition from one type of chemical control to the other.5  In a steam generator, free hydroxide can be produced by in-leakage of condenser cooling water impurities such as carbonate or bicarbonate anions. Free hydroxide can also be generated if the sodium to phosphate molar ratio is too high (>2.85). Although the bulk concentration of free hydroxide in the steam generator may be only a few mg/kg it can concentrate6  by factors >104 in areas of low flow for example, under tube support plates or in sludge deposits. This build-up of free hydroxide in local areas in combination with residual and operating tensile stresses can cause caustic cracking of austenitic stainless steels and high nickel alloys.

Subject
Materials, Tubes, Steam generators, Stress cracking, Thermal stress, Intergranular cracking, Stress, C ring stress corrosion testing, Tubing, Heat, Boilers, Heat treatment, Residual stress
© 1976 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).
1976
Association for Materials Protection and Performance (AMPP)
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