Solvent-free Epoxy Coating Aging Evaluation Method

The most direct and effect way to avoid metal corrosion is spreading anti-corrosion coating on metal surface. Solvent-free epoxy coating is an environmental protection anti-corrosion coating. It has broad application prospects. It has been widely used in anticorrosive measures of buried pipeline in gas transmission stations. Anti-corrosion coating will aging because of the envirmental and its own factors' influence. Followed, its corrosion residence will drop. In order to avoid metal corrosion, a reasonable assessment for coating aging degree should be given. At present, investigation on comprehensive evaluation of anti-corrosion coating's aging degree is less. And coating's appearance feature is the main basis of evaluation criterion available. This method requires more experience of evaluators, so it was influenced by subjective factors. In this research, electrochemical impedance spectroscopy (EIS) has been used to discuss solvent-free epoxy coating's aging process in simulated soil solution. Coating's aging stages were divided on the basis of the micro-procedure witch electrolyte solution penetration in coating and its corrosion reaction with metal. Coating's volume resistivity test circuit was designed by direct current electrochemical technology. Coating's volume resistivity was measured, and its variation rules in aging process were researched. EIS, coating's volume resistivity and coating's appearance feature were integrated for establishing a solvent-free epoxy coating aging comprehensive evaluation method. The main contents included:1. Solvent-free epoxy coating specimen was immersed to accelerate the aging rate. EIS in different soak period was tested, and was analysed by equivalent circuit. Coating aging process was analysed and the aging stages were divided.2. Solvent-free epoxy coating's volume resistivity test circuit was designed, and the volume resistivities in different aging periods were tested. Analysis show that coating's volume resistivity declined with the process of coating aging. The declining rate of the value of volume resistivity will accelerate with the aggravation of coating aging degree. Coating specimens which have the same aging degree but different thickness, got similar value of volume resistivities. That means the thickness of coating has no relationship with volume resistivity.3. Coating's EIS, volume resistivity and appearance feature were used as evaluation indexes. The method of mean-square deviation based on the principle of "differences in driver" was used for determining weight to evaluation indexes. Evaluation information aggregation model was established by the technique for order preference by similarity to ideal solution (TOPSIS) which based on performance indexes. Solvent-free epoxy coatings in different aging degrees were evaluated, the result shows that this method of comprehensive evaluation can give an accurate result of coating aging degree and divide aging grades.