Several leaks were observed in wall tubes located in the convection section of a package boiler after being in service for about 22 years. The design capacity of the boiler is 137 tons per hour (124.3 Megagrams per hour) at a maximum pressure of 15.6 barg (16 kg/cm2) and design temperature of 397°F (203°C). The failures occurred on the internal surfaces facing the hot gas at localized pits with hemispherical bottoms. Large tubercles, 0.43-inches (11 mm) in height and 0.24 to 0.47-inches (6 to 12 mm) in diameter, formed above the observed pits. The results of metallographic, SEM/EDS and XRD analyses are presented and discussed in this paper. A schematic model of a developed tubercle showing the individual layers and the distribution of detected elements in these layers is also presented. It was concluded that the tubes failed due to the presence of chlorides from sea water that contaminated the boiler feed water. Seawater contamination was caused by the severe corrosion damage of cupro-nickel tubes in the evaporator by shell side steam.

Subject
Pits, Water, Tubes, Iron, Corrosion detection, Tubercles, Internal surfaces, Boilers, Oxygen, Copper, Deposit corrosion, Elements, Chlorides
Keywords:
Package, boiler, convection, side, wall, tube, evaporator, cupro-nickel, deposit, chlorides
© 2007 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).
2007
Association for Materials Protection and Performance (AMPP)
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