Abstract
Electrochemical studies on the corrosion of API X65 pipeline steel after its immersions in 3.5% sodium chloride solutions for 1 h and 24 h have been reported by using open-circuit potential (OCP), cyclic potentiodynamic polarization (CPP), chronoamperometric current-time (CT) at -500 mV vs. Ag/AgCl and electrochemical impedance spectroscopy (EIS) measurements. OCP measurement for 24 h indicated that the potential of X65 steel increases in the less negative direction with time. CPP data revealed that increasing the immersion time to 24 h before measurements decreases the corrosion current density, the corrosion rate and increases the polarization resistance. The CT curves showed that X65 pipeline steel does not suffer pitting corrosion even after applying -500 mV vs. Ag/AgCl on the electrode for 65 min. EIS spectra confirmed that increasing the immersion time increases the surface and polarization resistances of the steel. All measurements were consistent with each other and showed clearly that increasing the immersion time from 1 h to 24 h before measurements leads to decreasing the corrosion rate and the corrosion resistance for the API X65 pipeline steel in the chloride test solutions.