Effect of Chromate Treatment on the Time for Blistering of Epoxy Coated Steel under a Temperature Gradient

Blistering of resin-coated steel is accelerated by a temperature difference across the resin. The time for blistering of epoxy-coated steels was measured under three temperature different conditions. The investigated factors were temperature difference, thickness of epoxy coating, quantity of chromate coating under epoxy coating. The time for blistering shortened with an increase in temperature difference, and lengthened with increases in film thickness and quantity of chromate coating. An experimental equation was derived from the the view points; (1) temperature difference and epoxy film thickness affect the rate of water permeation, (2) chromate coating affects the strength of the bonding of the epoxy coating to the steel. The derived equation shows that the time for blistering is a function of temperature gradient (=temperature difference/film thickness) and quantity of chromate coating. The time for blistering can be estimated by this equation under temperature different conditions.