| Abstrakt: |
In present investigation, failure investigation of failed economizer tube of boiler of the thermal power plant was analyzed through visual inspection, dimensional measurement, bulk chemical analysis, mechanical properties evolution and metallurgical analysis. Failure of the economizer tube was occurred in the form of cavity having one longitudinal hairline crack passing through the cavity on the external surface of economizer tube. Metallurgical failure analysis of an economizer tube was carried out by visual observation, chemical analysis, optical microscopy (OM), scanning electron microscopy, SEM-EDS analysis, x-ray diffraction (XRD) and mechanical properties evaluation. Ash deposit and surface corrosion were on outer surface were observed. Severe corrosion and thinning were observed on the external surface of economizer tube. SEM-EDS analysis on the fractographic samples near failure zone showed good amount of Cu deposition on the inner surface of the tube and ash-related corrosion products on the outer surface of the tube. Localized reduction/thinning of wall thickness of the economizer tube happened due to combined effect of ash corrosion-erosion from outside and pitting/galvanic corrosion from inner surface due to Cu deposition and finally resulted in failure of the tube. However, outer corrosion on the tube is significantly dominant due to ash corrosion. Therefore, ash corrosion is major cause of failure of economizer tube. Ash corrosion was due to use of poor-quality coal. To mitigate the problem, removal of ash deposition on outer surface and Cu deposition on inner surface of tube should be carried out by periodically by proper cleaning and use of good quality coal is suggested. [ABSTRACT FROM AUTHOR] |
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