In the fall of 1975, field data from two nuclear power plants indicated a reduction in the diameters of Inconel 600 steam generator tubes at their intersections within the tube support plates.1  The affected plants had operated for a long time on a phosphate water chemistry (13 to 15 months) and were subsequently switched to an all volatile treatment (AVT) using ammonia and hydrazine. Shortly after the switch to AVT (3 to 6 months), reductions in tube diameter, or "denting", were observed. At that time, the long phosphate chemistry prehistory was considered to be significant, since plants with little or no phosphate history were not denting. It was also considered significant that the plants that were experiencing denting used sea water or brackish water for condenser cooling and were therefore susceptible to higher, and more acid, levels of chloride contamination from condenser inleakage than fresh water plants. However, denting has been observed recently in plants that have had no phosphate history.

Subject
Acids, Water, Materials, Deformation, Nickel based alloys, Tubes, Autoclaves, Solids, Crevices, Phosphates, Magnetite, Carbon steel, Chlorides
© 1978 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).
1978
Association for Materials Protection and Performance (AMPP)
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