Graphitization of carbon steel boiler tubes resulting from long-term exposure to high temperatures is a commonly recognized phenomenon. Although graphitization causes a moderate reduction in metal strength properties, it has seldom been the direct cause of failure. However, recent investigations into the cause of tube ruptures has demonstrated an increased frequency of failures resulting directly from graphitization.

Two distinct forms have been identified. The first is that associated with the formation of aligned graphite nodules in heat affected zones of welds. The second, a more obscure form, is that associated with localized, plastic deformation of the tube wall. In this case, aligned graphite nodules may develop at any location where such deformation has occurred. The causes, identifying features, and remedial measures relating to both of these forms of failure are presented.

Subject
Carbides, Tubes, Iron, Nodules, Fissures, Graphite, Metals, Steel, Boilers, Carbon steel, Graphitization, Ferrite, Low alloy steel
© 1989 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).
1989
Association for Materials Protection and Performance (AMPP)
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