Pit growth and stifling on carbon steel in CO2-containing media in the presence of HAc

CO2 corrosion of carbon steel pipelines in the presence of acetic acid was studied using artificial pit electrode assembly. The potential difference and the coupling current between the small attack and the outer large surface were monitored by means of a zero resistance ammeter (ZRA). The results give strong and complementary evidence about the major role of acetic acid in the growth mechanism of localized attacks in CO2 corrosion. Pits seem to propagate and stifle mainly according to counteracting depletion effects of respectively acetic acid and CO2. It is also shown that the purely ohmic drop is not the only factor contributing to the stifling of localized corrosion attacks in systems like those of top of line corrosion. On the basis of the obtained results, a complete scenario was therefore proposed for the morphological trend of localized attacks, which is in good agreement with field observations.