A new method of paint damage for underfilm corrosion testing of painted galvanized steel was introduced. The method was based on the observation that the onset of underfilm creepback propagation in atmospheric exposures is preceded by the formation of red rust at the paint defect. Spotface panel damage, i.e., milling through organic and metallic coatings to create a large, unprotected source of red rust, was used to shorten the time needed to produce underfilm creepback in atmospheric exposures. The traditional scribe method of paint damage was used in the same tests. Statistical techniques were used to rank underfilm creepback performance on a variety of painted metallic coated steels and to provide rank correlations between scribe and spotface data. Spotface data collected at six months provided similar rankings and discriminating ability as scribe data collected after a 30 month atmospheric exposure.

Subject
Zinc rich coatings, Materials, Correlation, Corrosion products, Galvanized steel, Corrosion propagation, Steel, Rust, Metallic coatings, Coating defects, Zinc, Paints, Filiform corrosion
Keywords:
underfilm corrosion, atmospheric corrosion, cosmetic corrosion, paint, galvanized steel, electrogalvanized, zinc, corrosion testing, spotface, red rust
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1995
Association for Materials Protection and Performance (AMPP)
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