Study of sulphidation and chlorination on oxidized SS310 and plasma-sprayed Ni–Cr coatings as simulation of hot corrosion in fouling and slagging in combustion

The behaviour of two thermal sprayed Ni–Cr coatings compared to conventional SS310 was studied under pyrite, potassium sulphate and potassium chloride attack in inert atmosphere at 900 °C, as simulation of fouling and slagging in co-firing coal with biomass. The morphologic description of chemical attack by S, K and Cl and depth of penetration is performed using SEM, and EDX for chemical composition of scales. Sulphur from molten iron sulphide is able to penetrate through the coatings forming chromium and nickel sulphides, but in a less extent than in the preoxidised austenitic steel. The coatings proved to be resistant to molten potassium sulphate attack, which was catastrophic in the case of not-coated preoxidised SS310. The resistance of these materials against chlorination was tested and although both coatings were corroded by KCl salt, coating 1, with higher chromium content, hindered corrosion progression and protected steel matrix under coating.