Cause Analysis on Tube Bursting of Water-cooled Evaporating Screen of Boiler in a Chemical Plant Power Station

The steel tube of water-cooled evaporation screen in a boiler of a power plant had bursted for several times. The causes of tube bursting were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, microscopic analysis, scale layer analysis, X-ray diffraction analysis and water vapor quality analysis. The results show that scale formation on the inner wall of steel tube of water-cooled evaporation screen caused by water vapor target exceeding the standard, and the oxygen concentration in furnace feed water was seriously exceeded for a long time, which caused the oxygen corrosion under the scale, chloride ion corrosion and oxygen corrosion. Under the action of periodic stress, the cracks were formed on the inner wall of steel tube and deepened continuously, which eventually led to the tube explosion.