Effect of 2-Mercaptobenzothiazole concentration on the sour corrosion behavior of API X60 pipeline steel: Electrochemical parameters and adsorption mechanism
17 May 2020
Revised: 12 July 2020
Accepted: 28 July 2020
Available online: 30 July 2020
Abstract: The effect of 2-Mercaptobenzothiazole concentration on the sour corrosion behavior of API X60 pipeline steel in an environment containing H2S at 25 °C and at the presence of 0, 2.5, 5, 7.5 and 10 g/L of 2-Mercaptobenzothiazole inhibitor was investigated. In order to examine the sour corrosion behavior of API X60 pipeline steel, Open Circuit Potential (OCP), potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) tests were used. The Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) were also used to analyze corrosion products. The results of OCP and potentiodynamic polarization both showed that 2-Mercaptobenzothiazole reduces the speed of both anodic and cathodic reactions. Assessment of the Gibbs free energy of the inhibitor showed that it has a value of more than –20 kJ.mol−1and less than –40 kJ.mol−1. Therefore, the adsorption of 2-Mercaptobenzothiazole on the surface of the API X60 pipeline steel was occurred both physically and chemically. The latter was particularly intended to be adsorbed. Also, as the Gibbs free energy of the inhibitor took a negative value, it was concluded that the adsorption of 2-Mercaptobenzothiazole on the surface of the pipeline steel occurs spontaneously. The results of the EIS indicated that with increase of 2-Mercaptobenzothiazole inhibitor concentration, the corrosion resistance of API X60 steel is increased.An analysis of the corrosion products revealed that iron sulfide compounds are formed on the surface. In sum, the results showed that the increase of the inhibitor concentration results in a decrease in the corrosion rate and an increase ininhibitory efficiency (%IE). Additionally, it was found that 2-Mercaptobenzothiazole adsorption process on the API X 60 steel surfaces in a H2S-containing environment follows the Langmuir adsorption isotherm.And the adsorption process is carried out spontaneously.