Effects of turbulent flow on the corrosion inhibition properties of 2-mercaptobenzimidazole M. E. Olvera-Martinez, J. Mendoza-Flores, F. J. Rodriguez-Gomez, M. E. Palomar-Pardave and J. Genesca * The electrochemical techniques, that is, polarization resistance (R p ) and potentiodynamic polarization curves, were used in order to determine the effect of turbulent flow on the corrosion inhibiting effect of 2-mercaptobenzimidazole (2-MBI) on API 5L X52 grade steel samples immersed in a 3% NaCl aqueous solution saturated with CO 2 at 60 8C. Turbulent flow conditions were controlled using a rotating cylinder electrode (RCE). An inhibition efficiency of 98% was measured at a concentration of 10 ppm of 2-MBI at a rotation rate of 5000 rpm. This efficiency value is similar to those efficiency values measured at 25 and 40 ppm 2-MBI and at the same rotation rate. These observations suggest that as the turbulent flow conditions increase the corrosion inhibiting effect of 2-MBI is enhanced. 2-MBI follows a Langmuir adsorption isotherm. The calculated values of adsorption equilibrium constant (K ads ) and adsorption free energy (DG o ads ) suggest that the adsorption process taking place is chemical. The polarization curves indicate that the 2-MBI does not modify the electrochemical mechanism of the anodic (Fe dissolution) and cathodic (hydrogen evolution) reactions. It is suggested that 2-MBI decreases the rate at which these reactions occur, blocking the active sites on the steel surface. 1 Introduction In the oil and gas industries, the presence of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ) in the transported fluids causes severe corrosion problems in the steel pipelines [1–3]. In order to prevent and control this corrosion problem, several metallic materials, with better resistance, have been tested [4–6]. However, cost–benefit ratio is an important point in order to select a new material for the design and construction of pipelines. The use of chemical substances, known as corrosion inhibitors, added in low concentrations into a corrosive environment, reduces consider- ably corrosion rate in pipelines. Most of the corrosion inhibitors, used in the hydrocarbon transport pipelines carrying liquid streams containing CO 2 , are film-forming organic compounds, based on amine, imidazoline compounds, and their derivates [7, 8]. These corrosion inhibitors must form a uniform and adherent film on a metallic surface, and this film should withstand wall shear stresses associated to the movement of the fluid. Organic compounds containing sulfur have been found to be good corrosion inhibitors in CO 2 -containing environments [9]. It has been demonstrated that the heterocyclic compound, 2- mercaptobenzimidazole (2-MBI), is a good corrosion inhibitor for carbon steel [10–14], zinc [15], copper [16], and copper alloys [17], in acid environments (HCl, H 2 SO 4 , and H 3 PO 4 ). Figure 1 shows the chemical structure of 2-MBI. However, most of the published research has been carried out under static conditions, where there is no control of the wall shear stresses that could affect the integrity of the corrosion inhibitor film and, therefore, its efficiency. The objective of this work is to determine the effect of turbulent flow conditions on the inhibition properties of 2-MBI on carbon steel samples immersed in aqueous solution of 3% NaCl saturated with CO 2 at 60 8C. Materials and Corrosion 2012, 62, No. 9999 DOI: 10.1002/maco.201106323 1 M. E. Olvera-Martinez, F. J. Rodriguez-Gomez, J. Genesca Facultad Quı ´mica, Departamento de Ingenierı ´a Metalu ´rgica, Univer- sidad Nacional Auto ´noma de Me ´xico, UNAM, Ciudad Universitaria, 04510 Me ´xico D.F. (Mexico) E-mail: genesca@unam.mx J. Mendoza-Flores Instituto Mexicano del Petro ´leo, Direccio ´n Exploracio ´n y Produccio ´n, Eje Central L. Ca ´rdenas 152, C.P. 07730 Me ´xico D.F. (Mexico) M. E. Palomar-Pardave Departamento de Materiales, Universidad Auto ´noma Metropolitana Azcapotzalco, Av. San Pablo 180, C.P. 02200 Me ´xico D.F. (Mexico) J. Genesca Polo Universitario Tecnologia Avanzada, PUNTA-UNAM, PIIT Monter- rey, Apodaca, N.L. (Mexico) www.matcorr.com wileyonlinelibrary.com ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim