A laboratory study of mild steel vapour phase corrosion and its inhibition by dicyclohexylamine nitrite

A study was made of the corrosion of mild steel by acetic and formic acid vapours at 65, 75, 85 and 100% relative humidity (RH) and its inhibition by dicyclohexylamine nitrite (DICHAN). Electrochemical and gravimetric techniques were used. The corrosion rate of steel was in the range of <10-145 mdd and <10-35 mdd for 225 ppm acetic and 300 ppm formic acid vapours, respectively, at 65-100% RH. DICHAN has been found to provide moderate protection for steel at 65-85% RH. Inhibitor efficiencies were 64% and 71% in acetic and formic acids, respectively, at 100% RH. There is a reasonable correlation between inhibitor efficiencies estimates from weight loss, polarization and noise measurements. X-ray analysis of the corrosion products, in the presence and absence of DICHAN, shows the presence of magnetite (Fe3O4), as principal constituent, along with alpha-FeOOK and gamma-FeOOH. The acetic corrosion product film was of porous nature. (C) 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.