Carbon dioxide (CO2) related pitting and localized corrosion failures are of primary concern within the oil and gas industry. In environments saturated with both CO2 and H2S gas, the mechanisms by which pitting of carbon steel occurs can be complex and at times, unpredictable. The film formation characteristics and morphology in either CO2 and/or H2S-containing systems significantly influences the localized/pitting corrosion behavior of carbon steel materials. This paper presents the first part of a parametric study on pitting corrosion of carbon steel in CO2 saturated brines. This work examines the impact of changes in a key environmental parameter (temperature) on pitting corrosion processes of carbon steel in CO2-saturated NaCl brines. A pit propagation study is conducted over 168 hours based on changes in temperature and other measurable parameters such as in-situ pH of bulk solution, and the implications of such changes on the film properties and morphology are studied through a combination of electrochemical and surface analysis techniques (SEM and XRD). The possible galvanic effects of changes in film morphology and the influence of exposure time on pit initiation and propagation are discussed in an effort to elucidate the role of film morphology on pitting corrosion. The extent of corrosion damage of the carbon steel is evaluated through the implementation of surface interferometry to study discrete pit geometry; namely, the size and depth. The results indicate that pitting corrosion dominates total metal penetration at conditions where the morphology of the corrosion product layer is dominated by Fe3C and a form of iron carbonate often referred in the literature as amorphous iron carbonate. The continuous corrosion of surrounding surfaces also appears to be underestimating the growth of pits. Perhaps that detection of crystalline iron carbonate at 80°C coincides with reduction in rate of growth of pits.

Subject
Pits, Films, Steel surfaces, Materials, Corrosion rate, General corrosion rate, Corrosion products, Sodium chloride solution, Corrosion behavior, Crystal growth, Pitting, Carbon steel, Types of corrosion
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2014
Association for Materials Protection and Performance (AMPP)
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