Comparative evaluation of dicyclohexylamine and N-methyldiethanolamine as corrosion inhibitors for top of line corrosion on API X80 carbon steel in saturated carbon dioxide aqueous solutions

This work has evaluated the efficiency of selected volatile corrosion inhibitors in mitigation of top of line corrosion in wet gas pipeline at different temperatures. The main challenge of top of line corrosion in carbon dioxide rich environment is the ability of the volatile corrosion inhibitor to effectively mitigate corrosion at adverse conditions. Electrochemical corrosion experiments using potentiodynamic polarization method were conducted at temperatures of 20 ℃, 35 ℃ and 45 °C to evaluate the efficiency of dicyclohexylamine and n-methyldiethanolamine corrosion inhibitors for top of line corrosion inhibition on carbon steel specimens derived from API X80 natural gas pipelines. The electrolyte used, was an aqueous solution saturated with carbon dioxide, containing 200 ppm acetic acid and 1% NaCl solution, mimicking the corrosive environment in wet natural gas transportation. The results obtained show that the trend of corrosion inhibition efficiency decreased with increasing temperature such that the efficiency of 39.61%, 34.03% and 13.98% was achieved with dicyclohexylamine application and the efficiency of 34.53%, 15.30% and 6.26% was achieved with n-methyldiethanolamine at 20 ℃, 35 ℃ and 45 ℃ respectively. It was observed that dicyclohexylamine behaved as an anodic inhibitor while n-methyldiethanolamine exhibited cathodic inhibition behaviour. In conclusion, dicyclohexylamine was an effective volatile corrosion inhibitor over n-methyldiethanolamine for the selected steel in CO2-saturated environments at low temperatures below 35 ℃.