Investigation of Corrosion Inhibitive Effects of 2-Mercaptobenzoxazole and 2-Aminobenzimidazole on API-5L X60 in Sweet Corrosion Media

CO2 corrosion controlling was surveyed on carbon steel (API-5L X60) in NaCl 3.5 % (wt.) Solution saturated with CO2 by 2-Mercaptobenzoxazole (2MBO) and 2-Aminobenzimidazole (2ABI). Inhibition effects of these compounds were investigated by Scanning Kelvin Probe (SKP) as a new method and other techniques include; Weight loss, Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) in 50, 100, 200, 300 and 400 ppm concentration at 25, 40 and 60 oC in static condition. Weight loss results did not confirm effective efficiency for 2-Aminobenzimidazole as corrosion inhibitor on API-5L X60 in CO2 media but all tests results revealed 2-Mercaptobenzoxazoleacts as an effective inhibitor in this media on API-5L X60. The highest inhibition efficiency of 95%, 90% and 83.8% was obtained according to EIS, Potentiodynamic polarization and Weight loss tests, respectively at the concentration of 400ppm and 25oC. Adsorption isotherms of 2-Mercaptobenzoxazole showed physical and chemical adsorption process takes place on API-5LX60 surface. 2-Mercaptobenzoxazole adsorption obeys Langmuir isotherm model and affects on anodic and cathodic processes on metal surface so it’s performance is known as a mixed type inhibitor. Increasing of media temperature has reductive effect on 2-Mercaptobenzoxazole efficiency. Results of Scanning Kelvin Probe tests revealed surface potential of API-5L X60 is increased by 2-Mercaptobenzoxazole molecules that form a film on metal surface. This phenomena confirms that adsorption of 2-Mercaptobenzoxazole, more over the cathodic reactions, limits the metal surface affinity for anodic reactions of Fe atoms. Local corrosion potential on specimen surface was surveyed by use of surface potential maps (SKP map).