The use of corrosion–resistant weld overlays is now commonly used to reduce corrosion of boiler tubes in low NOx coal fired boilers. Alloys with higher chromium contents are the most resistant to corrosion in this type of service. A new alloy with high chromium has recently been introduced and has shown excellent resistance to corrosion in low NOx coal-fired environments. The new material is Alloy 33 (UNS R20033) and contains approximately 33% chromium, 32% iron and 31% nickel. The improved corrosion resistance of Alloy 33 should result in longer life of the weld overlay used to protect boiler tubes. Alloy 33 should also better resist circumferential cracking than the Mo-containing alloys now being used (such as Alloys 622 and 625); recent studies show that Mo segregation in weld overlays may be part of the circumferential cracking mechanism. After 18 months of service in a low NOx coal fired boiler, a field test on Alloy 33 weld overlay has demonstrated that it resists both corrosion and cracking.

Subject
Materials, Corrosion resistant alloys, Corrosion rate, Materials performance, Tubes, Molybdenum alloys, Corrosion cracking, Weight change, Corrosion scales, Oxide scales, Sulfidizing, Boilers, Alloys
Keywords:
Alloy 33, Alloy 622, Alloy 625, Sulfidation, Weld-Overlay, Cracking, Boiler, Coal-Fired, low NOx
© 2006 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).
2006
Association for Materials Protection and Performance (AMPP)
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