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 5000h of exposure time, comprising of 10 cycles each of 500h duration. Progress of the corrosion process was monitored using XRD and SEM-EDAX analysis of surface and transverse sections. An incubation period of about 1500h 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. © 2020 Elsevier Ltd. All rights reserved.