Tatiana Almeida, Jéssica Nogueira, Marcelo Tadeu Gomes de Sampaio, Eliane D'Elia, Oscar Rosa Mattos. In:AMPP Annual Conference + Expo, 2025, Nashville, EUA.
Resumo: RIP2025-00148: Corrosion models are crucial for estimating uniform corrosion. The understanding of CO2 corrosion mechanism has been extensively developed in the literature over the last 50 years. It is well known that CO2 enhanced corrosion of pipelines steel. The hydrogen evolution reaction increases in the presence of CO2 compared to a strong acid solution at the same pH. After years of discussions in the literature it was understood that CO2 acts as a buffering agent, where the dissociation of carbonic acid produces an additional H+ reservoir, which is the precursor of the cathodic reaction1-2. On the other hand, Almeida et al.3, using electrochemical impedance at OCP and calculation, demonstrated that, if CO2 was able to act on the free iron surface, producing (FeCO2)ads as reported in the literature4 its relaxations would appear as a capacitive loop. Thus, two consecutive capacitive loops should be seen. This diagram has never been observed since CO2 is not able to act on free iron surface. Nonetheless, if CO2are able to play any role in the corrosion mechanism, this can only be seen by polarizing the system.
Considering the above, electrochemical impedance was used to investigate the effect of CO2 on X65 carbon steel corrosion in different pH values. An experimental methodology was performed to polarize anodically and also cathodically the system, with small and fixed quantities of chloride, in the presence and absence of CO2.
The preliminary results at pH 3 and pH 4, show that in general, the impedance has two faradaic loops. The inductive loop is associated with relaxation of (FeOH)ads5. Hering, the diagrams clearly showed that CO2 does not act directly on the free iron surface, showing that the mechanism is not changed. However, a change in the characteristic frequency of the inductive loop in the medium containing CO2 was observed and highlight the role of CO2 in this corrosion mechanism. The mechanism of corrosion by CO2 will be discussed in this work, and a new reaction mechanism will be presented. These results and discussions bring new study perspectives to understand the effects of contaminants, such as SO2 and NO2, present in CO2 injection systems, and can elucidate the role of each contaminant in the carbon steel corrosion mechanism in CCS systems.
