Impact of Condensates Containing Chloride and Sulphate on the Corrosion in Automotive Exhaust Systems

The chemical composition of condensates recovered from a test car was systematically analysed in this study. It was found that most condensates contain a higher concentration of chloride than that of sulphate. In order to understand the effect of sulphate on the pitting behaviour of 436SS and to predict whether pitting will occur in these condensates, pitting potentials were determined in a 0.2M sulphate solution with varying chloride concentration by using the potentiodynamic cyclic polarization curve method. The results demonstrate that sulphate prevents pitting initiation of 436SS when the concentration of sulphate is higher than that of chloride. However, no inhibitory effect of sulphate was observed when the sulphate concentration is lower than the chloride concentration. As the condensate recovered from the muffler contains more chloride than sulphate, the muffler is most likely suffering from pitting. This was confirmed by the microscopic observation of the corroded muffler from the test car.