EVALUATION OF THE CO2 CORROSION RESISTANCE OF NEW LOW CHROMIUN STEELS USING FOR WELLS TUBING BY ELECTROCHEMICAL TECHNIQUES

Abstract

The present work was carried out to evaluate the CO2 corrosion resistance of carbon steels used for tubing in oil and gas industries. Two low  alloy  steels  containing  3% Cr,  identified  as  3CrA  and  3CrB,  were  studied by  electrochemical  techniques  (Chronopotentiometry, Voltamperometry, Electrochemical Impedance Spectroscopy and Linear Polarisation Resistance) coupled with a rotating disk electrode in order to control the hydrodynamic conditions of the system. Results obtained for 3% Cr steels were compared with those obtained for the conventional carbon steel, obtained from a N80 grade pipe, to evaluate the advantages of these new materials in terms of their CO2 corrosion resistance. Electrochemical tests were performed in a 3.5% NaCl solution previously deaereated and saturated with CO2 at 80 °C up to 72 h of immersion at 1000 rpm. Electrochemical measurements revealed that the corrosion resistance of low Cr steels is higher than that obtained for the carbon steel and decrease in the following order: 3CrB > 3CrA > N80. It is thought that these results might be explained  by  the  differences  found  in  the  metallurgical  characteristics  of  the  steels  (chemical  composition  and  microstructure).  In addition, it was found that the CO2 corrosion resistances of the steels increase with the immersion time, regardless of their chemical composition. This behavior was attributed to the formation of a corrosion product layer on the metal surface when the immersion time increases, mainly blocking the metal dissolution reaction.