Failure Analysis of an 18% Cr Ferritic Stainless Steel in a Simulated Exhaust Condensate Containing Urea

Exposure in the laboratory simulating a selective catalytic exhaust system component using urea injection for NO _x reduction and an artificial exhaust condensate in a diesel application has been performed. The hot, cyclic corrosion test was designed to simulate the conditions seen during use in a commercial vehicle application. The sample was subjected to a cyclic thermal gradient from ambient to a high of 500 °C and a 5% solution of urea containing sulfates, chlorides, and nitrates. During material evaluation for a selective catalytic exhaust component, a perforation was observed in a 439 ferritic stainless steel component. Examination of the sample found multiple modes of failure and multiple types of deposits from the urea test solution.