Electrochemical Analysis of Temperature, Concentration and Velocity Effects in Naphthenic Acid Corrosion of 5%Cr-1%Mo Steel

Abstract

The effects of temperature, velocity and naphthenic acids concentration in the corrosive mechanism of 5%Cr-1%Mo steel were studied in a dynamic autoclave by Electrochemical Impedance spectroscopy and Potentiodynamic Polarization Curves with an electrochemical cell of three electrodes: reference and counter electrode was made of Au and working electrode was 5%Cr-1Mo sample. The sample was exposed to mineral oil-naphthenic acids solutions to different concentrations and atmospheric pressure. Contrary to the velocity effect, the temperature has a huge influence in the steel corrosion: to 180°C the steel exhibits lower corrosion rate, however, increasing temperature promotes the thermal composition of complex naphthenic acids, reflecting a reduction in electrochemical polarization resistance, increasing the corrosion rate. Moreover, the temperature is closely related to the concentration acid effect, since the kinetics of corrosion changes significantly when the system is subjected to higher temperatures. These results were complemented with surfaces characterizations by SEM and EDX.