Effect of porosity on resistance of epoxy coatings to cold-wall blistering
- Lehigh Univ., Bethlehem, PA (United States)
Electric utilities use polymer coatings for corrosion protection in a variety of locations, such as cooling towers, water boxes, and tubesheets. In some cases, these coatings are vulnerable to failure in areas where a temperature gradient exists between a cold substrate and relatively warm fluid (cold-wall blistering). 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 substrates and exposed to heated water for up to 10 months in Atlas test cells as a modified version of NACE Standard TM0174. The performance of the coatings was measured by the exposure time for the coatings to start blistering, the time for the corrosion potential of the coating substrates to shift toward active values, and the delamination rate of the coatings. Good cold-wall blistering resistance was observed for two polyamine-cured epoxy coating systems with porosity levels < 1 vol%. These two coating systems exhibited longer lifetimes than the other coating systems under four different test conditions that varied coating thicknesses and exposure temperatures. Intermediate performance was observed for a polyamine-cured epoxy with an average porosity level > 1 vol%. Poor cold-wall blistering resistance was shown by a polyamide epoxy system, an amine adduct epoxy system, and an amido-amine epoxy system, all of which had porosity levels > 1 vol%. Most of the coating 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 resistance to cold-wall blistering also showed the lowest blistering 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.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 136979
- Journal Information:
- Corrosion, Vol. 51, Issue 11; Other Information: PBD: Nov 1995
- Country of Publication:
- United States
- Language:
- English
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