Effect of microstructure on scale protectiveness and corrosion rate of carbon steel in CCTS environments

The paper reports the results of an experimental work on the effect of steel microstructures on morphology and protectiveness of the corrosion scale formed in water saturated by supercritical CO2. Two HSLA steels were tested. The microstructures were modified by means of different heat treatments. Weight loss tests were measured after exposure at pressure of 80 bar and 60°C temperature. The morphology of the scale was analyzed by means of scansion electron microscope (SEM) energy - dispersive X - ray spectroscopy (EDX). Cathodic potentiodynamic tests were carried out on pre-corroded specimens for evaluating the effect of pre-formed scales on cathodic polarization curves in CO2 saturated sulphuric acid solution at pH3, which is the value estimated for waters saturated by supercritical CO2. The results are discussed in order to evaluate the effect of iron carbide network on scale growth and corrosion rate.