Leakage occurred in more than 21 tubes of reformed gas (waste heat) boiler tubes during a hydrotest after 8 years of service life. The tube material is low alloy carbon steel SA213 T11 with outer diameter (OD) of 38.1 mm (1.5-inches), 5.15 mm (0.2-inch) wall thickness and length of 6858 mm (270-inches). Leaks occurred due to localized external surface metal loss, which penetrated at the interface of the hot end of an internal ferrule, about 9 cm (3.5-inches) away from the boiler feed water (BFW) inlet. The presence of deposits was also observed on the external surface of the tube. This paper describes the observed failures of tubes and presents the results of the conducted lab analyses. The observed localized damage occurred due to a caustic gouging corrosion mechanism. This corrosion resulted from a significant temperature gradient, and the subsequent deposition of concentrated alkaline salts. Several recommendations are provided to avoid similar failure in the future.

Subject
Pits, Scanning electron microscopy, External surfaces, Corrosion failures, Materials, Salts, Microstructure, Tubes, Gouging, Surface layers, Boilers, Copper, Deposit corrosion
Keywords:
Reformed gas (waste-heat) boiler, deposit, copper, ferrule, boiler feed water, temperature gradient, caustic gouging, localized depression
© 2005 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).
2005
Association for Materials Protection and Performance (AMPP)
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