Study of Carbon Dioxide Corrosion Products by X-Ray Diffraction

Internal carbon dioxide corrosion is one of the most common types of corrosion in gas field development. The results of studying the composition of carbon dioxide corrosion products by X-ray diffraction are presented. FeCO₃ is the main product resulting from dissolution of steel upon carbon dioxide corrosion. Siderite is characterized by the phenomenon of isomorphism in the crystal structure (a change in the chemical composition of the phase at the same crystal structure). Here, some iron ions in FeCO₃ can be replaced by manganese, calcium, and magnesium ions. It is found out that the phases of the formed precipitates with a nonstoichiometric composition (Ca_xMg_yMn_zFe)CO₃ have poor crystallinity. This is associated with the presence of defects in the crystal structure. They will exhibit poorer protective properties when compared to stoichiometric FeCO₃, the film of which is packed, uniformly distributed, and tightly adheres to the steel surface. An analysis of the diffraction patterns evidences good crystallinity of FeCO₃, the shape of the particles of which tends to a regular hexagonal habitus. The results obtained can be used in studying the resistance of corrosion products formed on the internal surfaces of gas production equipment under aggressive conditions in the presence of CO₂ in produced and transported hydrocarbons.