## 2 Experimental Development
### Electrochemical Tests in Corrosion Loop
Electrochemical studies with rotating cylinders assess inhibitors' capacity to prevent carbon steel corrosion under a centrifugal force. They are tools that are commonly used to assess corrosion inhibitors' performance in oil fields [46; 47; 48; 49; 50; 51]. As shown in Table 1 and Figure 2, at a constant inhibitor concentration (150 ppm) and under the aforementioned work conditions, the performance of the corrosion inhibitor (inhibition efficiency) depends on the working electrode rotation speed (shear stress). In most of the cases we studied, the higher the rpm, the higher the corrosion current (CC); that is, the higher the general corrosion rate, the lower the inhibitor's efficiency [52]. [PERSON] et al. [52] obtained similar results when working with RCE at rates of 0, 100, 1000, 2000, 3000, 4000, 5000, and 6000 rpm, and using API 5L X52 steel cylindric samples as working electrodes in 5% NaCl solutions, at 60 \({}^{\circ}\)C, with saturated CO\({}_{2}\), and at different concentrations of the used inhibitor. As can be seen in Figure 3, in this work, Inhibitor 1 was the one with an efficiency of over 90%, thus having a Rank 2 general corrosion, according to [PERSON]'s criterion. We cannot speak of the efficiency of an inhibitor if there is localized corrosion. Efficiency against corrosion is defined as efficiency against general corrosion. If there is a localized attack, it is not possible to have efficiency values, given that there is inefficiency; that is, an inhibitor is not efficient if the material undergoes a localized attack (pitting, stress corrosion cracking, corrosion fatigue, etc.). This information is crucial for the corrosion engineer, given that an inhibitor that produces pitting endangers the security of the oil field's facilities. On the other hand, the fluid flow regime is one of the parameters that have a great effect on the surface rate. The type of flow regime affects the thickness and velocity of the water layer flowing up the tubing, and it defines the shear stress and mass transfer at the steel surface [53; 54; 55]. Flow loop tests are an important complement because they represent the closest experimental laboratory condition to assess the performance of those inhibitors that are used in the oil and gas industry. The selected flow rate, 1.2 m/s, is the same as that of the pipeline fluids of oil companies in Neuquen, Argentina. FL tests evince problems that involve corrosion, erosion, abrasion, two-phase fluids, the time the inhibitor takes to coat the graduated cylinders, the period during which the inhibitor works, etc. Table 3 shows the differences between the CR relative to the weight loss of corrosion coupons C1 and C2. The CR values found in corrosion coupon C1 were higher than those found in coupon C2. This is because C1 was on the upper part of the pipeline (Figure 3), where it came into contact with two-phase fluids (CO\({}_{2}\) gas + NACE solution), whereas corrosion coupon C2 was on the lower part of the pipeline, where it was in contact with the NACE solution +  
Figure 5: Pictures of the tested samples for each inhibitor. The circles and yellow arrows show the presence of localized corrosion (20\(\times\)). dissolved CO\({}_{2}\). Table 3 shows the CR relative to the mean LPR of each inhibitor obtained with the Aquamate Corrater Instrument. These were within the CR value range obtained for each weight-loss coupon. When assessing corrosion inhibitors, [PERSON] et al. [56] applied NACE G 170 in an FL test using a liquid solution containing pressurized CO\({}_{2}\). With the FL equipment they used, they determined the instantaneous corrosion rate with RLP and Tafel polarization curve (TPC) measurements, as well as the efficiency against the corrosion of the inhibitors, which was tested statically and dynamically at a 0.5 m/s flow rate. We can obtain more information on this study by looking at Figure 6 (analysis of the first graphic of Figure 4), which corresponds to Inhibitor 1, where we can see different zones in which the inhibitor works.