Laboratory and field evaluation of organic corrosion inhibitors in sour media

Abstract

The expensive and insidious character of corrosion problems encountered in various industries requires appropriate corrosion-monitoring techniques. The specific advantages of using on-line electro-chemical impedance spectroscopy (EIS) to accomplish such a task can be put to profit by analyzing the experimental data points automatically with a mathematical permutation technique. The polarization resistance values calculated from the EIS measurements can then be translated into overall resistance to corrosion. Additionally it is shown that the constant phase element (CPE) necessary to model most EIS results can indicate the progress of localized corrosion. The laboratory evaluation of two proprietary organic inhibitors by EIS measurements showed the two inhibitors to be equally effective in the inhibition of sour gas induced corrosion. Microscopically measured pit depths on exposed carbon steel specimens could additionally be correlated to the integral of the depression angle produced by the CPE. A series of EIS measurements made in a field-pipe loop also showed these two organic inhibitors to be similarly very effective. A post-test analysis of the monitoring electrodes by various surface profile examination techniques revealed the existence of a strong correlation between the extent of pitting corrosion and the CPE analyzed from EIS measurements.