Corrosion behavior of three iron-based model alloys in reducing atmospheres containing HCl and H2S at 600°C

The corrosion of three Fe-xCr alloys (x = 8, 12, 18 wt.%) was examined at 600 C in reducing atmospheres containing HCI and H2S with two different H2S contents and compared with the behavior of the same materials in H2S-free H-2-CO2 and H-2-HCI-CO2 mixtures producing similar oxygen and chlorine pressures. Exposure to the low-H2S gas mixture had only a reduced effect on the behavior of Fe-8Cr and Fe-18Cr, but increased significantly the corrosion rate of Fe-12Cr. Increasing the H2S level accelerated the corrosion of all the alloys, but particularly that of Fe-18Cr. In both cases only minor amounts of sulfur and chlorine were present close to the alloy/scale interface. An increase of the Cr content reduced the corrosion rate in both HZS gas mixtures, especially in the range 812 wt.% Cr, due to a larger volume fraction of Cr2O3 in the scale. The results have been discussed on the basis of the thermodynamic stability diagrams of the Fe-O-Cl-S and Cr-O-Cl-S systems. (c) 2006 Elsevier Ltd. All rights reserved.