Water wall tubes from boiler operating since 14 years were subject to repeated failures ranging from pinholes to cracks and ruptures. A failure analysis on received tube was carried out including destructive and non-destructive testing. Feedwater, drum water and live steam qualities were evaluated based on the data provided by the plant authority. The results obtained through this study indicate a mechanism of caustic gouging inducing hydrogen embrittlement. The root causes determined were improper carryover control and waterline creation by low flow and/or high blow down rate. Therefore, it was recommended to conduct a total inspection of the boiler to determine the extent of the damage. As preventive maintenance, a more strict control of the carryover is necessary through the monitoring of sodium/phosphate ratio, reduction of oxygen up to the permissible level, fixation of the chemical boiler treatment dosing problems.

Subject
Hydrogen embrittlement, Corrosion failures, Water, Materials, Microstructure, Tubes, Inspection, Waterline, Waterwalls, Boilers, Copper, Deposit corrosion, Elements
Keywords:
Boiler tubes. Caustic gouging, hydrogen embrittlement, waterlines, carryover, under-deposit corrosion
© 2017 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).
2017
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.