Coating Evaluation and Validation of Accelerated Test Conditions using In-Situ Corrosion Sensor

By G.D. Davis, L.A. Krebs, C.M. Dacres

An in-situ corrosion sensor was used to obtain electrochemical impeda nee spectroscopy (EIS) me11- surements on coated panels under a variety of accelerated laboratory test conditions as well as ambient exposure at a Florida beach. Three studie are reported. The first compared the sensor (EIS) measurements taken innalt fog chamber to those obtained using a clamp-on cell and tl1e conven­tional remote electrode/immersion approach. For coatings with minimal ed_ge defects, the two methods gave equivalent result .

For coatings with edge de­fects, the sensor was able to detect the defects provided the surface was wet, as in the salt fog chamber. 111 contrast, the conventional approach was unable to detect defects unless the tj were within the confines of the clamp-on cell.

In the second sensor measure­ments were used to compare canting degradation during salt fog acrylic corrosion test,humidity, and immersion. to that occuring at a Florida beach. The cyclic corrosion test showed an excellent correla­tion. with beach expo ure ·while the salt fog and other test showed very little correlation, suggesting that the cyclic test is more valid for discriminating coating performance for seacoast exposure. The sensor also indicated that the test could be short­ened by up to 40% without significantly reducing the validity of the test. ln thefinalexample,a series of primers and appliques were evaluated using the cyclic corrosion test. The sensor EIS results al­lowed a discrimination between the materials ets even though there was  little or no – usual difference between the specimens.