ASSESSING PERFORMANCE OF PAINTED CARBON AND WEATHERING STEELS IN AN INDUSTRIAL ATMOSPHERE

Protective properties and electrochemical impedance characteristics of four painted steels were investigated after outdoor exposure for 6 ye ars and laboratory-based immersion tests. Results were compared to eva luate performance of the two paint systems for different steel substra tes. The silicate-type primer/epoxy-based micaceous iron oxide (MIO) p aint/polyurethane topcoat system showed better performance than the ep oxy-type primer/epoxy-based MIO paint/polyvinyl chloride (PVC) topcoat system. The former paint system showed better topcoat protection and more effective cathodic protection (CP) provided by the zinc-rich prim er. Two forms of paint degradation blistering and pore attack, were ob served. Paint degradation was correlated with changes In paint resista nce and the breakpoint frequency of impedance data. Based upon visual observation and changes in impedance characteristics, two impedance mo dels were proposed to explain the paint degradation.