Corrosion Behavior of Pipeline Steel X65 in Oilfield

Abstract

The inner- and outer- surface corrosion behavior of X65 pipeline steel used in Shengli Chengdao oilfield was studied in this paper. The inner surface corrosion behavior of X65 pipeline steel in oil-water mixtures with different flow rate and oil content was examined by means of mass loss method and electrochemical technique. The corrosion resistance of the outer surface of X65 pipeline steel in soil extracts was also examined by means of polarization curves and electrochemical impedance spectroscopy (EIS). The phase constituents and surface morphology of corrosion products were characterized by using X-ray diffraction techniques (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that the corrosion rate of X65 steel increased with the increasing flow rate of oil-water mixture, which could reach the maximum value when the oil content was 0.5% (mass fraction). The corrosion current density of X65 steel increased with immersion time in soil extracts. A loose corrosion product film formed on the steel surface, which can accelerate the cathodic depolarization reaction.