ABSTRACT
The degradation experienced by metallic components during exposure to process environments of the types encountered in coal conversion plant has prompted considerable research during recent years. These atmospheres generally have low levels of oxygen but high sulphur and carbon activities and therefore sulphidation is one of the primary modes of attack.
In such multi-component environments there is a competition between sulphur, oxygen and carbon to react with the alloy. It is therefore important to establish the factors which govern the formation of a surface oxide and whether this remains intact or, alternatively, becomes disrupted by faster growing sulphides.
The experiments detailed in this paper have been designed to address this problem using a range of H2-CO-H2O-H2S gas mixtures of varying sulphur activity. Several techniques have been used to monitor the nucleation and growth of oxides and sulphides formed on the surfaces of Fe-Cr-Ni alloys during exposures ranging from a few minutes to several hundred hours at 800°C. A sequential SEM technique coupled with cross-sectional metallography has been invaluable in helping establish the corrosion mechanisms involved.
