Evaluation of the tendency of coil-coated materials to blistering: Field exposure, accelerated tests and electrochemical measurements

The tendency of coil-coated hot dip galvanized materials to blistering was investigated in accelerated tests and by electrochemical impedance spectroscopy. The best prediction of outdoor performance at a marine test site was obtained in the Q-panel condensation test (QCT) at 60 °C with the minimum testing time of 500 h. The ratio of the impedance modulus at 60 and 25 °C measured at a low frequency of 0.1 Hz correlated with the extent of blistering after outdoor exposures and accelerated tests. It is proposed that this parameter reflects the interaction of the polymer and the metal/polymer interface with water.

► Q-panel condensation test at 60 °C best predicted the tendency to blistering.
► The test reliability increased with the test duration.
► EIS parameters correlating to the extent of blistering have been identified.
► Low-frequency impedance modulus reflects interface stability in presence of water.