Powerplant boilers operating at maximum load with tubing surface temperatures in superheaters and reheaters at 590°C (1100°F) or above have experienced increased deposit formation and higher fireside corrosion rates from compounds of vanadium, sodium, and sulfur. Methods used to combat the increased fuel-ash corrosion include (1) derating the boiler by lowering outlet steam temperatures, (2) use of additives to control the corrosive compounds, (3) application of refractory and composite coatings, (4) installation of metal shielding, (5) blending of high-grade coal to lower sulfur and ash, and (6) use of improved tubing materials. Nearly all such methods have disadvantages. Derating is costly because of lower heat rates, increased fuel consumption, and the need for greater control of attemperation. Additives are often ineffective and tend to plug sections and cause hot spots, introducing new maintenance, cleaning, and removal problems. Coatings have so far been ineffective1  while shielding lowers heat transfer and adds to maintenance costs.

Subject
Sulfur, Materials, Substrates, Nickel based alloys, Tubes, Chromium, Welding, Tubing, Bending, Interfaces, Reheaters, Boilers, Alloys
© 1979 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).
1979
Association for Materials Protection and Performance (AMPP)
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