Study of Adsorption/Desorption Effect of 2-Mercaptobenzothiazole as Sweet Corrosion Inhibitor on API-5L X60 Steel

Abstract

In this study, the inhibitive performance of 2-mercaptobenzothiazole (2MBT) and 2-aminobenzothiazole (2ABT) were investigated on API-5L X60 steel as corrosion inhibitor in NaCl 3.5 wt % solution saturated with CO2 at 25, 40 and 60°C. The 2ABT compound due to the formation of bicarbonate salt and carbamate does not have good performance as a corrosion inhibitor. Adsorption/desorption effect of 2-mercaptobenzothiazole was studied by electrochemical impedance spectroscopy (EIS) techniques. Adsorption effects of 2MBT on Volta potential of metal surface were studied by mapping via Scanning Kelvin Probe (SKP) method. Volta potential changes in the presence of inhibitor follow corrosion parameters fluctuations that were observed in the other test results with respect to bare metal. Results showed that the 2MBT had adsorption/desorption behavior on metal surface during immersion. Inhibitive properties of 2MBT was studied by weight loss, potentiodynamic polarization and EIS. 2-Mercaptobenzothiazole had effective inhibition performance with 97% efficiency at 300 ppm concentration and excellent adsorption during immersion in sweet corrosion media. Adsorption of 2MBT on the surface of API-5L X60 obeys the Langmuir isotherm model. The value of $${\Delta}G_{{{\text{ads}}}}^{^\circ }$$ showed that 2MBT adsorbs on API-5L X60 surface via physical and chemical adsorption processes. 2-Mercaptobenzothiazole increases activation energy of metal dissolution in CO2 saturated solution. Slope change of anodic and cathodic branches in polarization plots revealed that this compound acts as a mixed type inhibitor. Increasing of test media temperature decreases inhibitive power of 2-mercaptobenzothiazole. Contact angle measurements revealed hydrophobic effect of 2-MBT absorption on to sample surface.