Effect of 2-mercaptobenzothiazole concentration on sour-corrosion behavior of API X60 pipeline steel: Electrochemical parameters and adsorption mechanism

We investigated the effect of the 2-mercaptobenzothiazole concentration on the sour-corrosion behavior of API X60 pipeline steel in an environment containing HS at 25°C and in the presence of 0, 2.5, 5.0, 7.5, and 10.0 g/L of 2-mercaptobenzothiazole inhibitor. To examine this behavior, we conducted open-circuit potential(OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy(EIS)tests. Energy dispersive spectroscopy and scanning electron microscopy were also used to analyze the corrosion products. The results of the OCP and potentiodynamic polarization tests revealed that 2-mercaptobenzothiazole reduces the speed of both the anodic and cathodic reactions. An assessment of the Gibbs free energy of the inhibitor(■) indicated that its value was less than-20 kJ·moland greater than-40 k J·mol. Therefore, the adsorption of 2-mercaptobenzothiazole onto the surface of the API X60 pipeline steel occurs both physically and chemically, the latter of which is particularly intentional. In addition, as the ■dsvalue was negative, we could conclude that the adsorption of 2-mercaptobenzothiazole onto the surface of the pipeline steel occurs spontaneously. The EIS results indicate that with the increase in the 2-mercaptobenzothiazole inhibitor concentration, the corrosion resistance of API X60 steel increases. An analysis of the corrosion products revealed that iron sulfide compounds form on the surface. In summary, the results showed that an increase in the inhibitor concentration results in a decrease in the corrosion rate and an increase in inhibitory efficiency. Additionally, we found that the 2-mercaptobenzothiazole adsorption process on the API X60 steel surfaces in an H2 S-containing environment follows the Langmuir adsorption isotherm and occurs spontaneously.