Sulphur dew‐point corrosion resistant mechanism of austenitic stainless steels

Abstract

Sulphur dew‐point corrosion occurs in the low temperature parts (<200°C) of heavy oil fired boilers such as economisers, air preheaters, and chimneys. Its mechanis proposed by Kowaka et al suggests that corrosion proceeds in three steps as shown in Figure 1. The first step is corrosion in sulphuric acid at low temperature and concentration, the second step is in sulphuric acid at high temperature and concentration, and the third step is in boiler deposits containing sufficient amounts of unburned carbon and sulphuric acid at high temperature and concentration. The overall corrosion rate was suggested to be mainly determined by the third step due to its much longer time compared with those of first and second steps. Kowaka et al also proposed a test method in the mixture of concentrated sulphuric acid and activated carbon for developing sulphur dew‐point corrosion resistant low alloy steels, and the results were well correlated with the actual field tests. This report extensively covers the corrosion behaviours of austenitic stainless steels which might have practical applications in high temperature environments.