The possibility of grain boundary microstructural changes occurring in mill-annealed Inconel alloy 600 tubing at steam generator operating temperatures was investigated in the present study. Two aspects were considered: (1) Are microstructural changes likely to occur? (2) If they do occur will they affect the tubing corrosion resistance? Two heats of mill-annealed, thermally treated and solution-annealed Inconel alloy 600 steam generator tubing were annealed in the 371°C to 649°C (700 to 1200°F) temperature range and evaluated for microstructural changes. The data were extrapolated and it was concluded that microstructural changes are unlikely to occur at steam generator operating temperatures. This conclusion was substantiated by detailed microstructural analysis of mill-annealed Inconel alloy 600 tubing removed from operating steam generators and C-rings that had been exposed in an autoclave at 332°C (630°F) for 73,250 hours. It was further concluded that if microstructural changes do occur which are immeasurable, they will not have an adverse effect on SCC resistance.

Subject
Materials, Carbides, Precipitation (solids), Nickel based alloys, Operating temperatures, Chromium, Steam generators, Tubing, Heat, Sensitization, Annealing, Grain boundary, Alloys
© 1984 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).
1984
Association for Materials Protection and Performance (AMPP)
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