Protective properties and electrochemical impedance characteristics of four painted steels were investigated after outdoor exposure for 6 years and laboratory-based immersion tests. Results were compared to evaluate performance of the two paint systems for different steel substrates. The silicate-type primer/epoxy-based micaceous iron oxide (MIO) paint/polyurethane topcoat system showed better performance than the epoxy-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 primer. Two forms of paint degradation, blistering and pore attack, were observed. Paint degradation was correlated with changes in paint resistance and the breakpoint frequency of impedance data. Based upon visual observation and changes in impedance characteristics, two impedance models were proposed to explain the paint degradation.

Subject
Primers, Top coats, Zinc-rich primers, Impedance, Pores, Steel, Rust, Immersion, Corrosion protection, Corrosion resistance, Zinc, Blistering, Paints
Keywords:
atmospheric corrosion, blistering, carbon steel, cathodic protection, electrochemical impedance, epoxy, immersion testing, industrial environments, polyurethane, pore attack
NACE International
1997
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