Effects of Time, pH and Cl^- Concentration on Electrochemical Corrosion Behavior of Filmed Pipeline Steels

Polarization curves and electrochemical impedance spectroscopy (EIS) were used to study the effects of time, pH and Cl- concentration on electrochemical corrosion behavior of filmed X65 and X70 steels. The investigation indicated that Nyquist diagrams of both the filmed pipeline steels included a high frequency capacitive loop and a low inductive arc, implying two time constants. The coverage of film formed under different conditions was extremely good, but its density was poor, and the occurrence of its further active dissolution was limited. Effects of time, pH and Cl- concentration on corrosion electrochemical behavior were closely related to the film characteristics, the filmed X70 steel with a full and none stress rupture film would be more difficult to suffer further corrosion and was less sensitive to Cl- concentrations than X65.