Laboratory scale tests on corrosion behavior of boiler materials in simulated combustion atmospheres (EU Project – OPTICORR)

Abstract

Laboratory scale tests were made in the Plant Simulation Test Laboratory (PSTL) at JRC IE Petten and at VTT Industrial Systems in Finland. The multi-sample exposure tests were carried out under isothermal conditions at temperatures of 500 and 600 °C in N2-8% O2-15% H2O, N2-8% O2-15% H2O-2000 vppm HCl and N2-8% O2-15% H2O-200 vppm SO2 atmospheres. The experiments were focused mainly on common ferritic and austenitic steels such as X10, X20, 2.25Cr1Mo, AC66, Sanicro28, Esshette 1250 etc. A Scanning Electron Microscope (SEM), with Energy Dispersive Spectrometer (EDS), and X-ray diffraction (XRD) techniques were used to determine the chemical and phase composition of the corrosion products. The obtained results show that the presence of SO2 generally suppresses the oxidation rate of ferritic materials. Suppression of the oxidation rate in an SO2 containing atmosphere could be due to the presence of sulphides at metal/scale interfaces , which probably influences the ion transport through the oxide scale. When the oxidation reaction is surface controlled, absorbed sulphates interfere with the reaction of the oxygen on the surface. The presence of HCl in moist air at temperatures of 500 °C and 600 °C accelerates the oxidation rate of the studied materials, especially for the ferritic steels. The SEM/EDS studies suggest that in HCl containing atmospheres the corrosion mechanism is „active oxidation”︁.