Corrosion properties of type 409L and 436L stainless steels in condensed waters were evaluated to predict the life time of muffler in automotive exhaust system. Laboratory and field tests were carried out to establish the optimum condition of acceleration test simulated. From the inspection of the muffler extracted from the field-tested cars after driving for 24 months, a large amount of chloride and sulfate was detected in the corrosion products and these ions were also detected in the condensed water. Especially, the concentration of the sulfite detected in the condensed water was above 200ppm. Muffler could be heated up to above 250 oC during driving at the speed of 100 km/hour and the humidity in muffler could be increased up to above 90% during idle driving.

The passive zone was not detected in type 409L stainless steel during the anodic polarization in the artificial condensed waters and the corrosion current became higher with increase of the concentration of chloride and sulfite. However, type 436L stainless steel showed passive behavior in artificial condensed water though the passive current was slightly increased at higher concentrations of those ions. From the results of field and electrochemical tests, the simulation test condition was determined. Three types of condensed waters having different contents of chloride and sulfite ions were used at the simulation test. The corroded depths measured on the stainless steels after the simulation test, where the ionic concentrations were 300 ppm Cl-, 1000 ppm SO42-, and 600 ppm SO32- were similar to the depth obtained from field test. The simulation test showed that the life cycle of the type 436L stainless steel was three times longer than that of type 409L stainless steel.