Effect of flow velocity and entrained sand on inhibition performances of two inhibitors for CO2 corrosion of N80 steel in 3% NaCl solution

Inhibition for CO₂ corrosion of N80 steel by quaternary alkynoxymethyl amine (IMC-80-Q) and imidazoline in 3% NaCl solution was investigated under static and flowing conditions by using modified rotating disk apparatus. The effects of flow velocity, concentration of inhibitor as well as entrained sand on inhibition performances were studied through weight loss test, scanning electron microscope (SEM) observation and electrochemical techniques including electrochemical impedance spectroscopy (EIS), linear polarization resistance. Electrochemical parameters such as R_t and C_d for IMC-80-Q exhibited peak-value-phenomenon at inhibitor concentration of 150 mg/L when flow rate was below 5 m/s, in contrast with 300 mg/L when flow rate was beyond 5 m/s. The optimum concentration was further enhanced by the entrained sand in the medium containing IMC-80-Q. The adsorption of IMC-80-Q under static condition obeyed Langmuir isotherm when inhibitor concentration was below 150 mg/L, but it changed into Freundlich isotherm as inhibitor concentration was beyond 150 mg/L. The optimum inhibitor concentration of imidazoline under static condition was 100 mg/L, but it increased to 200 mg/L at 5 m/s. Under static condition imidazoline exhibited better inhibition than IMC-80-Q did; in contrast, at 5 m/s IMC-80-Q exhibited better inhibition than imidazoline did. The critical flow velocity was a function of both inhibitor type (IMC-80-Q or imidazoline) and inhibitor concentration.