Hot corrosion of alloy 617 OCC in simulated coal ash environment encountered in USC power plants

Abstract Hot corrosion of Alloy 617 OCC was studied in a simulated coal ash environment at 700 °C. A synthetic mixture of sulphates of alkali metals Na and K and oxides of Al, Si and Fe was used to simulate the coal ash environment developing in advanced thermal power plants. Studies extended up to 5000 h of exposure time, comprising of 10 cycles each of 500 h duration. Progress of the corrosion process was monitored using XRD and SEM-EDAX analysis of surface and transverse sections. An incubation period of about 1500 h was observed, characterised by formation of a single protective layer of chromium oxide, with little or no corrosion damage occurring. Longer exposure times saw formation of a second layer, comprising of oxides of Co, Ni, Fe etc, bringing in significant corrosion. Aluminum and Ti were found to be internally oxidised. The manuscript elaborates on these findings.