Surface sulphide formation on high-temperature corrosion resistant alloys in a H2S-HCl-CO2 mixed atmosphere

In this paper the corrosion behavior of high temperature corrosion resistant alloys is investigated in a gas atmosphere containing HCl and H2S at 480 degrees C and 680 degrees C. By considering the vapor pressures of the metal chlorides and the water gas shift reaction, as well as the influence of H2S, the different corrosion behavior at 480 degrees C compared to 680 degrees C can be explained and a model of the course of corrosion is proposed. Corrosion tests were performed for 240 h with the austenitic stainless steels S31400 (20 wt% Ni) and N08811 (30.4 wt% Ni) and with the Ni-based alloy N06600 (72.5 wt% Ni). It could be shown that with increasing Ni-content in the alloy, the corrosion rate at high temperatures decreased, but this effect could no longer be observed at lower temperatures. While for N08811 and N06600 the mass loss was lower at 680 degrees C, it increased at temperatures of 480 degrees C. In the case of S31400 the mass loss increased with rising temperature.