Leakage of water-cooled wall tube in subcritical boiler

Abstract

Usually, heating surfaces used in thermal power plant boilers include economizers, water-cooled walls, superheaters, and reheaters, abbreviated as the “four tubes” of boilers. The leakage of the heating surface is a common form of unplanned shutdown in thermal power plants, accounting for more than 50% of abnormal shutdown accidents of units. Once the heating surface explosion occurs, the thermal power plant needs to shut down for treatment, resulting in huge losses in power generation and fuel consumption during startup and shutdown. This has a huge impact on the safety production and economic benefits of the enterprise. In this paper, the leaked water-cooled wall tube in the subcritical boiler was studied by means of microstructure analysis, hardness test, energy spectrum analysis, chemical composition test, macro-morphology inspection, and tensile test. The results revealed that the oxygen concentration difference between the area installed in ceiling pouring material and the area exposed to the air can result in significant differences in electrode potential between different areas of the front water wall tube passing through the ceiling. An oxygen concentration difference battery is formed. In this way, the water-cooled wall steel pipe continuously corroded and thinned. Finally, perforation leakage occurred under the pressure of the internal high-temperature medium.