Given the great damage caused by corrosion of metals in various oil and gas industries and the use of coatings as a simple and efficient way to prevent corrosion, it is important to provide an industrial method for eva‎luating the performance of these coatings. Therefore, in this study, an attempt was made to eva‎luate the performance of the glass-flake/epoxy coating by monitoring the resistance of the sample and confirming the accuracy of the results with the results of electrochemical impedance spectroscopy, which is abundant in the literature. In the first part of this study, a suitable cell for DC resistance measurement was designed and the effective parameters for the measurements were optimized. Then, a long-term corrosion test was performed on one of the samples received from the refinery (carbon steel substrate with primer and glass-flake/epoxy coating). The sample was placed in the designed cell and exposed to accelerated corrosion conditions at 60°C and a corrosive solution of 3.5% sodium for 43 days. However, before measuring the resistance of the sample, in order to eliminate the effect of temperature on the resistance of the sample, the temperature of the cell and the sample inside it were brought to ambient temperature. The resistance of the sample in the dry state was very high, about 210 GΩ, but two hours after the injection of the salt solution, it decreased to 22.1 GΩ. This significant decrease is due to the penetration of the solution into the coating indicating the presence of porosity in it and insufficient barrier performance. In addition, the presence of micropores in the coating surface was confirmed with the morphological analysis of the coating surface. After the sample was placed in a corrosive medium (saline solution and a temperature of 60 °C) for 24 hours, its resistance decreased by more than 99% and reached 175 MΩ. From then until the twentieth day, the resistance increased to 557 MΩ, which could be due to corrosion occurring on steel/coating interface, accumulation of corrosion products, and the formation of a passive non-conductive layer in the substrate, which can cause delamination of the coating. From the twentieth day to the last day of the test (day 43), the resistance change had a decreasing trend and reached 210 MΩ on the last day. This decrease may also be due to the formation of conductive pathways in the coating due to the passage of electrolyte in it and also due to massive corrosion in the metal substrate. During the nine-day exposure of the specimens to 3.5% sodium chloride solution at 60°C, the mean OCP values for the specimens CS, A, B, and C were -0.6404 05 0.023, 3600 08 0.064. -0-, 0/2242 09 0.017, -0.2680 06 0.043 V vs. SCE, respectively. The more negative open circuit potential values for the specimen CS as well as its negative trend indicate that uncoated carbon steel is quite susceptible to corrosion under these conditions. For all coated samples, the open circuit potential values were always less negative. Two time constants were observed in the impedance plots of the samples even at the very beginning of the exposure. For the samples, the values of charge transfer resistance and pore resistance were extracted on different exposure days. For all samples, a sharp decrease in charge transfer resistance and pore resistance was observed from the first minutes of exposure to one day later. From the first to the sixth day

محمد ژياني

محمد محمدي تقي آبادي، كيوان رئيسي

حسن حداد زاده، محمد محسن مومني