Contrast inversion of ferrite and pearlite in a sweet corrosion environment

In-situ optical imaging in a confocal Raman system of a pipeline steel under sweet corrosion environmental conditions typical of a commercial environment (NaCl brine, pH 6.8, temp, 80 degrees C, low oxygen, open circuit potential) revealed contrast inversion of ferrite and pearlite microdomains as compared to their 3% Nital etched counterpart. This behaviour is in excellent agreement with the time resolved mineralogy growth profile obtained from in-situ confocal Raman and also complemented by AFM and SEM analysis of the surface roughness and corresponding morphology. The data presented here provides new insight into the process of sweet corrosion scaling in a ferritic-pearlitic microstructure steel.