Effect of Porosity on Resistance of Epoxy Coatings to Cold-Wall Blistering

摘要

Six epoxy-based coating systems were tested for their resistance to degradation in the form of "cold-wall" blistering. The coatings were applied to type 1010 steel (UNS G10100) sub-rates and exposed to heated water for up to 10 months in Atlas test cells as a modified version of NACE Standard ",10174, The performance of the coatings was measured by f exposure time for the coatings to start blistering, the time i the corrosion potential (Ecar) of the coating substrates to shift toward active values, and the delamination (or blistering) rate of the coatings. Good cold-wall blistering resistance as observed for two polyamine-cured epoxy coating systems with porosity levels 1 vol percent. Poor cold-wall blistering resistance was shown by a polyamide epoxy system, an 'line product epoxy system, and an amido-amine epoxy system, all of which had porosity levels > 1 vol percent. Most of the at ting samples exhibited linear blistering rates, which indicated that the kinetics of cold-wall blistering were diffusion controlled. The two coating systems that showed the best stance to cold-wall blistering also showed the lowest Storing rates, indicating that these coatings may have had lower permeabilities and/or better adherences than the poorer performing coatings, probably as a result of their lower porosity levels and similar compositions.