Corrosion inhibition by fatty acid oxadiazoles for oil well steel (N-80) and mild steel

Three long chain fatty acid oxadiazoles namely 2-undecane-5-mercapto-1-oxa-3,4-diazole (UMOD), 2-heptadecene-5-mercapto-1-oxa-3,4-diazole (HMOD) and 2-decene-5-mercapto-1-oxa-3,4-diazole (DMOD) were synthesized in the laboratory and were evaluated as corrosion inhibitors for mild steel in 15% HCl at 105±2°C by weight loss method. Inhibition tests were also carried out on N-80 steel under similar conditions in 15% HCl containing 5000 ppm of UMOD. The results obtained indicated that oxadiazole derivatives are good corrosion inhibitors. UMOD was found to be the best corrosion inhibitor. It exhibited 94% inhibition efficiency for N-80 steel and 72% inhibition efficiency for mild steel. Potentiodynamic polarization studies carried out at room temperature on mild steel in 15% HCl, containing 500 ppm of oxadiazole derivatives and on N-80 in 15% HCl containing 500 ppm of UMOD showed that all the investigated compounds are of mixed type inhibitors. The adsorption of all the oxadiazoles was found to obey Temkin’s adsorption isotherm