A NOVEL METHOD OF TESTING AND MONITORING ANTICORROSION ORGANIC COATINGS

A brief review of accelerated and electrochemical methods of testing and assessing the corrosion prevention afforded by organic coatings is followed by results using one particular accelerated and one particular electrochemical test. The accelerated test was the hot salt bath test. This operates at 55-degrees-C and is claimed to give results in only 10 days. The electrochemical technique, here employed to monitor the protection afforded both at intact face areas and at breaks in the coating, i.e. scratch areas, was d.c. resistance measurement. Two slightly differently formulated standard grey electrocoat paints were examined. These had been coated on a number of different zinc substrates and on cold rolled steel and prior to coating half the specimens had been phosphated. Results showed a very good correlation between the d.c. resistance measurement and visual assessment indicating the usefulness of this kind of measurement to achieve quantitative data and to monitor remote, visually inaccessible areas. The hot salt bath test produced good differentiation. Using a statistical approach, large differences were seen in the behaviour of the different substrates and smaller differences were seen between the two paints. Further work is in hand to find out the extent to which these results correlate with other more standard accelerated tests (c.g. salt spray: both continuous and cyclic type) and with service experience.