2. Corrosion Inhibition of X52 Pipeline Steel in Chloride Solutions Using Nonionic Surfactant

Two concentrations of NPE-4 nonionic surfactant and corrosion inhibitor (CI) commercially available were added to NaCl (2.45 % and 3 %) and ocean water solutions (OWS) in order to study the corrosion process of API X52 pipeline steel. Corrosion inhibition of X52 pipeline steel in chloride solutions was evaluated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. EIS analyses showed that 3 % NaCl was the more corrosive solution for X52 steel. Adding CI to 3 %NaCl solution improves the corrosion resistance of X52 steel; however, adding CI to OWS, the corrosion control of X52 steel was more evident preventing the pitting, salts embedding, and corrosion under deposits. X52 steel exposure to solutions adding surfactant as corrosion inhibitor after having been evaluated through polarization curves displayed low corrosion rates (0.88 mm/year). Standard free energy calculation suggested that surfactant is adsorbed physically into the X52 steel surface. Meanwhile, it was observed that CI was more difficult to adsorb on X52 steel surface, and consequently corrosion was higher than adding surfactant to chloride solutions.