Abstract
Pitting and localized corrosion of carbon steel is considered to be a complex process influenced by a wide range of parameters such as temperature, bulk solution pH and chloride ion concentration to name a few. Solution pH is known to influence corrosion film characteristics and morphology in CO2 and H2S-containing systems. However, from the perspective of pit initiation and propagation in CO2-saturated environments, the extent to which in-situ pH of solutions and the presence of corrosion products influence localized attack is still not clearly understood. This paper presents an investigation into the role of in-situ pH on the corrosion product characteristics and the pitting behavior of X65 carbon steel in CO2-saturated brine over a wide range of environment acidity/alkalinity. Pit propagation studies are conducted over 168 hours at 500C in 3.5 wt.% NaCl buffered solutions to identify the role pH plays on corrosion product film morphology and chemistry and the underlying influence this has on the propagation of pits within each environment. Corrosion film composition and morphology are identified through a combination of electrochemical and surface analysis techniques, which include scanning electron microscopy (SEM) and x-ray diffraction (XRD). The extent of corrosion damage of the carbon steel is evaluated through the implementation of surface interferometry to study discrete pit geometry; namely, the size and depth.
