An Investigation of the Overall Corrosion Behaviour of X65 (UNS K03014) Carbon Steel in Different H2S-CO2- Containing Environments.

There have been increasing concerns related to the challenges posed by sour corrosion to the integrity of oilfield pipeline steels. In environments containing variable quantities of both C02 and H2S gas, the corrosion behavior of carbon steel can be particularly complex. An understanding of the mechanisms, sequence of electrochemical reactions and impact on the integrity of carbon steel materials in these environments is still not clearly understood. The film formation process, characteristics and morphology in C02 and H2S- containing systems are also known to be different depending upon the environmental and physical conditions, influencing the rates of both general and pitting corrosion. Questions still remain as to how the combined presence of C02 and H2S gases at different partial pressure ratios influence the corrosion mechanisms, as well as initiation and propagation of surface pits. This paper presents an investigation into the overall (i.e. general and localized) corrosion behavior of carbon steel in CO2/H2-containing environments. The work explores the impact of changes in ratios of C02 and H2S partial pressures at both 30 and 80°C in a 3.5 wt. % NaCI solution. All experiments are performed at atmospheric pressure, while H2 content is varied at 100,10,000 (1 mol. %) and 100,000 ppm (10 mol. %). Pitting corrosion is also evaluated up to 168 hours to determine the impact of increasing H2S content on the extent of localized corrosion. Corrosion film properties and morphology are studied through a combination of scanning electron microscopy and X-ray diffraction. The extent of corrosion damage of the carbon steel is evaluated through the implementation of surface interferometry to characterize pitting corrosion.