HOT CORROSION STUDIES ON VARIOUS BOILER TUBE STEELS AND SUPER ALLOYS

Abstract

Hot corrosion studies were conducted on uncoated boiler steel and superalloys specimens after exposure to air and molten salt at 900°c under cyclic conditions.The thermogravimetric technique was used to analyze the corrosion products.The samples after oxidation were examined by SEM and XRD for surface analysis. The samples were then cut and mounted for cross-sectional analysis by EPMA. Three types of substrate materials were used: low carbon steel ASTM-SA210 grade Al (GrA1); 1Cr— 0.5Mo steel ASTM-SA213-T-1 I (T11); and 2.25Cr— 1Mo steel ASTM-SA213-T-22 (T22). These materials are used as boiler tube materials in some of power Plants in northern India. GrAl has a wide range of applications in boilers, especially in the construction of the water walls. When the service conditions are more stringent from the point of temperature and pressure, the other two types of steel mentioned above are employed. Two types of super alloys are used : iron based — superfer800H and nickel based -superni75.These Super alloys have been developed for high-temperature applications. However, these alloys are not always able to meet both the high temperature strength and high temperature corrosion resistance simultaneously, their behaviour under severe corrosive enviornment have been studied