This paper deals with three cases of boiler tube failure.

1). Flow assisted chelant corrosion was concepted as reason for inadmissible thinning of economizer tubes. There were discontinuous orange peel and extremely thin layer of iron oxides on those scalloped waterside. Some pearlite grains with iron leached off were found in surface vicinity under oxides layer.

2) Caustic gauging was recognized as damage mechanism of evaporator arch tube. The failure was localized in vicinity of protruding weld seam. It had character of ellipsoidal funnel with solid dense piece of iron and copper oxides inside and thin sodium contained deposit between the deposit and tube surface. The last was significantly etched under the deposit.

3) Quasi corrosion cracking was real cause for bent tube rupture by an axial crack. Neither internal attack nor significant structure degradation was observed in crack vicinity. The crack sides were strongly oxided and ash constituents penetrated into the crack. Nothing like said was found in neighborhood, hence the fault tube was “pre-cracked” before its service beginning, for instance due to inefficient heat treatment after bending.

Subject
Pits, Water, Materials, Metal surfaces, Tubes, Iron, Corrosion cracking, Corrosion attacks, Oxide surfaces, Mechanical failure, Weld seams, Boilers, Deposit corrosion
Keywords:
boiler tubes, water side corrosion, caustic gauging, FAC, corrosion cracking
© 2008 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).
2008
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.