Injection of inhibitors is an economic and efficient way to combat corrosion of tubular steels utilized in the production and transmission of oil and gas. Given variability in the physicochemical environments encountered in the field, small scale laboratory testing is necessary to determine the effectiveness of inhibitors in specific corrosive environments. To achieve ppm concentrations of an inhibitor in a small-scale lab setup, the inhibitor often needs to be pre-diluted before addition to the test electrolyte, which has the potential to introduce experimental errors. One factor that affects the repeatability of corrosion inhibition testing is the volume of solvent used to dilute or dissolve the small amount of inhibitor prior to addition to the test environment. In this study electrochemical measurements, including linear polarization and potentiodynamic polarization, were utilized to evaluate the effect of different volumes (0.1 mL to 3 mL) of isopropanol used as a solvent for imidazolinium, pyrimidinium, and phosphate ester inhibitor model compounds in 2 L of a brine; a commercial corrosion inhibitor was also studied for comparison purposes. The cathodic charge transfer rate was affected more when a relatively large amount of isopropanol was used to dilute the inhibitor. However, in a well-inhibited system initially without isopropanol, the cathodic charge transfer remained unaffected by the addition of isopropanol at the conclusion of the experiments. This suggests that the usage of organic solvents for dilution of inhibitors for small volume corrosion tests should be carefully reviewed before testing.
Corrosion inhibitors is commonly used to combat internal corrosion of mild steel pipelines in oil and gas production and transmission systems. Since the corrosive environment and flow conditions could vary in different fields, small scale laboratory testing is essential to determine the effectiveness of inhibitors in specific corrosive environments. To ensure the accuracy of inhibitor dosage in a small-scale lab setup, the inhibitor often needs to be pre-diluted before addition to the test electrolyte. This pre-dilution has the potential to lead to experimental errors. However, little information can be found about pre-dilution steps, and their influence on inhibition phenomena, in the open literature.
