Unlike liquid-phase inhibitors, volatile corrosion inhibitors (VCI) can adsorb on the surface from the vapor phase and spontaneously penetrate into crevices and slots, as well as reach surfaces of complex -shaped articles that are difficult to coat. The VCI vapors saturate thereby the humidity condensed e.g. on internal pipeline surfaces, to form a necessary protective film. The main advantage of a VCI lies in the possibility to protect all of the inside surfaces that are in contact with both the liquid and vapor medium. The advantages of these inhibitors are very important for the protection of long-distance pipelines and equipment which have complex shapes including slits, cavities and small
clearances. However, many unsolved problems still remain concerning the optimal use of VCI. The role of volatility, solubility, basicity, and other
features of VCI in their efficiency against the CO2 corrosion of steel are discussed. Some examples of a quantitative approach to the prediction of optimal chemical structure of VCI are demonstrated.
Keywords: adsorption, CO2 corrosion, corrosion inhibitor, pH adjustment, volatility, volatile corrosion inhibitor