High Temperature Corrosion Failure of a Secondary Superheater Tube in a Thermal Power Plant Boiler

摘要

Failures of boiler tubes are a foremost cause of the unscheduled outages of the thermal power plant boiler. The failure of the boiler tubes occurs due to various reasons like creep, fatigue , corrosion and erosion. This paper highlights a case study of typical premature failure of a platen superheater tube of thermal power plant boiler. Visual examination, dimensional measurement, chemical analysis, oxide scale thickness measurement, microstructural examination, Energy Dispersive spectroscopy (EDS) were carried to ascertain the probable cause/causes of failure of inner leg of platen super heater tube. From the investigation, it was finally concluded that the presence of potassium (K) and sulphur (S) in the deposited ash may be responsible for formation of low melting compound alkali- iron trisulfate. The combination of localized high tube metal temperature and wall thinning due to high temperature fireside corrosion led to the premature tube failure.