The inhibitive behavior of Quebracho tannin extract on SAE 1010 steel corrosion in the acidic media is investigated. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) are first used to determine the inhibition efficiency of Quebracho in 0.1 M HCl solution to identify the best extract concentration to subsequently evaluate the inhibitor activity in CO2‐rich aqueous solution at high pressure (15 MPa) and high temperature (70°C). Polarization curves revealed that Quebracho extract acted as cathodic inhibitor and that the inhibition efficiency is dependent on the extract concentration. The EIS measurements and SEM analysis showed that the inhibitor had been adsorbed on the steel surface. The inhibition efficiency of Quebracho in CO2 medium was similar to the 0.1 M HCl, reducing expressively the corrosion rate. The SEM images and X‐ray diffraction analysis showed that iron carbonate was the main corrosion product formed on the metal surface in CO2‐rich environment in the presence of Quebracho. Besides, the corrosion scale was thinner and more compact in the presence of inhibitor.

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The corrosion inhibiting effect of the tannin from Acacia mearnsii bark on API 5CT K55 steel, used for casing in the oil and gas industry, was investigated in 1 M HCl medium with different tannin concentrations. Corrosion was monitored by electrochemical tests using potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). Complementary analyses of the corroded surfaces were performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X‐ray diffraction (XRD). With the application of A. mearnsii tannin, the cathodic branch of the PP curves shifted to lower corrosion current density values. EIS analysis indicated that inhibitor molecules were adsorbed on the steel surface, which provided protection against corrosion. The SEM, AFM, and XRD data showed that in the presence of the inhibitor, a film and amorphous material were adsorbed on the steel surface, plausibly associated with the formation of tannates. The highest inhibition efficiency was obtained at an inhibitor concentration of 0.7 5 g L−1 (92% determined by PP and 98% by EIS), and a high degree of surface coverage was observed, compared with that obtained using the other concentrations of tannin.

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