Investigation and Analysis on Corrosion Environment of Automotive Exhaust Systems

Abstract

Field survey on the corrosion life of exhaust systems was performed to determine, the ranking between external and internal corrosion, and also the effect of the engine type and the catalytic converter type to internal corrosion. Concurrently, analysis of condensates and corrosion products were carried out to make clear the difference in corrosion environment which results from the difference in type of engine and type of catalytic converter. It was found that corrosion life is limited mainly by inner corrosion, and the corrosion of exhaust systems equipped with three-way catalytic converter was most aggressive relative to conventional types of engine and catalytic converter. In the corrosion environment of exhaust systems equipped with three-way catalytic converter, it was found that SO₄^2-, SO₃^2-, HCO₃^2-, and HCHO exist usually, and very high concentration of Cl^-exists in some cases, while organics such as CH₃COO^-and HCOO^-do not exist. From the analysis of corrosion products, it was found that SO₄^2-and Cl^-are enriched to the corrosion interface.