Effect of substituted imidazoline inhibitors on hydrogen uptake by a carbon steel undergoing hydrogen sulfide corrosion

Several substituted imidazoline inhibitors have been studied under the conditions of hydrogen sulfide (H2S) corrosion to determine how they inhibit the penetration of hydrogen into the St3S carbon steel (CS, equivalent to AISI CS 1020) immersed in aqueous chloride solution-hydrocarbon phase mixtures. Custom-made hydrogen (electrochemical and vacuo-electrochemical) microprobes were used for measurements. Seven pure substituted-imidazoline inhibitors of a well-defined chemical structure and three Polish commercial imidazoline-type inhibitors used in the refinery industry were investigated. The pure substituted-imidazoline inhibitors were found to protect the clean surfaces very efficiently and the precorroded steel surfaces less efficiently. The time of adsorption of the inhibitors was determined. Adsorption of the substituted imidazoline inhibitors was found to be chemical in nature and to follow Frumkin's isotherm. Each inhibitor examined reduced the hydrogen uptake by the CS. Commercial inhibitors were more effective in protecting the steel against corrosion than against hydrogen uptake. Provided the dosage was adequate, the inhibitors protected the CS against hydrogen uptake down to levels higher than the critical hydrogen concentration.