*3.2. E*ff*ect of Time*

The effect of immersion time on the corrosion inhibition efficiency of the tested inhibitor was also assessed in this paper. Figure 5 and Table S3 show the corrosion rate and the corrosion inhibition efficiency after 168 h of immersion in the presence and absence of 1.0 g L−<sup>1</sup> of GA at different CO2 partial pressures at 25 ◦C. It follows from the table that GA still shows a very high *IE* even after a longer immersion time. However, it should be noted that *IE* slightly decreases after 168 h of immersion, compared to the one observed after 24 h of immersion.

**Figure 5.** Corrosion inhibitor efficiency obtained at different CO2 partial pressures after 24 and 168 h of immersion at 25 ◦C.

This behavior has also been reported by several studies [36,37]. The decrease in *IE* may be due to the desorption of the inhibitor from the metal surface, which makes the protective layer unstable. In this study, the desorption of GA is likely ascribed to its deprotonation due to the consumption of CO2 from the tested solution because of the electrochemical reactions occurring into the system [5,38]. This leads to a decrease in the acidity of the solution and shifting the Equation (12) towards the deprotonation of the inhibitor.

These results confirm that GA is effectively able to protect the steel surface from sweet corrosion at high CO2 partial pressures even after a prolonged immersion time, reflecting a strong molecular adsorption of GA on the metal surface and the formation of a stable protective layer.
