Simulated Fireside Corrosion of Ni-Base Alloys in Oxy-Fired Conditions at 700°–800°C

Abstract

One future objective for coal-fired power generation is to develop advanced ultrasupercritical (A-USC) boilers that incorporate oxy-firing to facilitate carbon capture. The steam condition goals of 760°C/34.5 MPa will require major materials changes throughout the boiler, including Ni-base alloys in the hottest sections. Solution hardened alloys such as 740 and 282 are needed to meet the strength requirements for 760°C. In previous work, little difference in corrosion rate was found between air- and oxy-firing for alloy 740 at 600°–800°C so laboratory testing focused on the “worst case” oxy-firing conditions with higher CO2, H2O and SO2 than expected with air-firing. Model alloys were made to investigate the roles of Cr, Al, Ti, Co and Mo on the fireside corrosion behavior. Exposures conducted for 500h at 700° and 800°C found that Al and Ti additions typically reduced the extent of attack under these conditions. As expected, the alloy Cr content had a substantial effect between 18 and 22%. Additions of 4% and 8%Mo to Ni-20Cr-(0-20)Co alloys increased the metal loss at 800°C and Ni-20Cr-20Co-(0-8%)Mo showed the highest attack at 700°C. The much higher attack of alloy 282 at 800°C can likely be attributed to its lower Cr content compared to alloy 740, which was developed to have excellent fireside corrosion resistance. Paper published with permission.