9Cr steel has been widely used for boiler tube, header and pipe because of the excellent high temperature strength.

It is well known that the creep failure is anticipated in weld joint, like Type four cracking due to the low creep strength in softening zone of heat affected zone.

On the other hand the creep failure of 9Cr steel tube itself has been reported also. The creep failure is due to the hot spot generated by the obstruction of heat transfer in the part where the steam oxidation scale is exfoliated (not spalling-off).

The service time of some 9Cr steel tubes have reached to 20 years and the total scale thickness has been beyond 300μm. The clarification of creep failure of 9Cr steel tube by scale exfoliation must be a keen issue for users.

The user group in Japan has been organized to project the research for safe and long utilization of 9Cr steel tube by the analysis of the tubes for long time service.

As the result, in all boilers investigated, scale exfoliation inside the tube occurred. But the reduction of the hardness is not found if there is no creep failure. This means that creep damage may not occur below the temperature of tube 900K.

Subject
Materials, Tubes, Exfoliation, Metals, Heat, Scale thickness, Scale, Boilers, Creep, Steam, Hardness, Voids, Oxidation
Keywords:
9Cr, Boiler, Tube, Super heater, Steam, Creep, Rupture, High Temperature, Oxidation scale, Heat Transfer
© 2011 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).
2011
Association for Materials Protection and Performance (AMPP)
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