Economizer water-wall damages initiated by feedwater impurities

Abstract

The main causes of efficiency loss in thermal power plants are boiler tube failures that diminish unit reliability and availability, and raise the cost of the electric energy. For that reason, the regular examination of boiler tubes is indispensable measure for prevention of future malfunctions of power units. The microscopic examination of economizer's inner wall microstructure, the analysis of chemical composition of deposit using X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) have been performed in a subcritical power plant. Stress corrosion cracking, pitting corrosion, destroyed protective magnetite layer, presence of magnetite and hematite in deposit and corrosive impurities within the cracks have indicated the effect of inadequate quality of feedwater that cannot entirely ensure reliable operation of the boiler. It may be stated that maintenance of present boiler does not provide its reliable operation. The extensive chemical control of water/steam cycle was recommended.