Abstract
The effect of increasing the immersion time form 1 h to 24 h on the corrosion behavior of API X-70 pipeline steel in 4.0 wt. % NaCl solution was reported using different electrochemical and spectroscopic techniques. The cyclic potentiodynamic polarization (CPP) measurements indicated that increasing the time of immersion decreases the anodic, cathodic and corrosion currents. Chronoamperometric current-time (CCT) experiments at -0.5 and -0.35 V vs. Ag/AgCl showed that the absolute current of the steel decreases with increasing immersion time and that pitting corrosion occurs only at -0.35 V as indicated also by scanning electron microscope images. Electrochemical impedance spectroscopy (EIS) confirmed the results obtained by CPP and CCT that the increase of immersion time from 1 h to 24 h increases both the solution and polarization resistances. Results together were consistent with each other confirming that the corrosion of API X-70 5L pipeline steel in 4.0 wt. % NaCl solution decreases with increasing time due to the formation of oxide and/or corrosion product layers on the surface.