Corrosion Behavior of X-70 Pipe Steel in Crude Oil Environments Depending upon Surface Characteristics

The electrochemical behavior of X70 pipeline steel as a function of surface characteristics was investigated by potentiodynamic Tafel scan, R p / E c , potentiostatic and electrochemical impedance spectroscopy (EIS) in tap water, crude oil extract, and oil-in-water emulsion. The results demonstrated that polished surface was more corrosion resistant than rough surface in tap water due to passivation and oil/water emulsion by uniform surface coverage of the oily phase. Furthermore, the severity level of electrolytes for both surfaces increases from tap water to oil-in-water emulsion and crude oil extract, respectively. The inductive behavior of steel surfaces at high-frequency domain in EIS spectrums was attributed to destabilized structure of electrolyte near the surface. High polarization resistance and admittance values of capacitance for both surfaces in oil/water emulsion depicted greater corrosion resistance independent to surface morphology. The results of R p / E c and potentiostatic were in support for both surfaces in all three electrolytes.