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Development of An Electrochemical Method For Field Testing of Protective Coatings

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University of Southern California Los Angeles United States

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Nine different coating systems on cold rolled steel were tested by recording EIS-data during immersion in 0.5 N NaC1 open to air. One set of samples tested was in the as-received condition and an artificial defect applied. Another set of samples were tested after 2 years of outdoor exposure at Cape Canaveral, FL For this set, the susceptibility to cathodic delamination was also evaluated. The as-received condition samples were tested for 1 year. The sample with an all-latex coating was eliminated from further testing since the coating was so porous that the impedance spectra resembled those usually found for bare steel. In long term testing, alkydenamel, alkyd enamel Si-alkyd, and the zinc-rich primerepoxy polyamidepolyurethane coatings were damaged. For set of samples tested for 55 days after being outdoors, the only coating damage detected was the alkydenamel Si-alkyd coating. The coating properties degraded faster than the as-received sample, indicating that outdoor exposure had weakened the coating. In the cathodic delamination tests, the largest amount of damage occurred on the other alkyd-based coatings.

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Technical Report,01 Jul 1990,31 Dec 1991



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Approved For Public Release;

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