Abnormal high metal wastage rates were discovered in the reheater of a boiler at the Williams Station on South Carolina Electric & Gas Company, which had been converted from oil to coal firing in 1983. Originally, liquid coal ash corrosion was suspected as the cause of the accelerated corrosion. To confirm this, test spools of austenitic alloys with varying chromium content were installed in the most corrosion prone areas and exposed for 17,431 hrs. It was found that the metal loss rate, ranged from 15-21 mils/yr was independent of the chromium content of the alloy. Microscopic examination indicated that the high corrosion rate was probably due to alternating oxidizing and reducing conditions, which caused the formation of iron and sulfur rich scales, enhanced by fly ash erosion in areas of high gas velocity.

Subject
Sulfur, Tubes, Chromium, Sulfates, Metal wastage, Iron, Metal loss, Corrosion scales, Oxide scales, Scale formation, Boilers, Coal, Alloys
Keywords:
corrosion, boilers, coal, superheaters, reheaters
© 1994 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).
1994
Association for Materials Protection and Performance (AMPP)
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