Pitting Corrosion of Carbon Steel in CO2-Containing NaCl Brine

Abstract

Studies of the susceptibility of carbon steel (line pipe steel) to pitting were performed at room temperature in deaerated, NaCl-saturated CO2-containing solution simulating natural brine. Measurements of different kinds were made in a wide range of pHs and electrode potentials. The primary corrosion product was identified by x-ray diffraction analysis as Fe(HCO3)2. This compound was found to form a tight, adherent film on the metal surface. Longer exposures caused transformation of Fe(HCO3)2 into FeCO3 in the form of a porous, non-adherent and non-protective layer. Pitting resulted from the action of galvanic couples between different sites on the steel surface, either uncovered or screened by porous layers of various corrosion products.