Study of carbon dioxide corrosion products by the X-ray diffraction method

The internal carbon dioxide corrosion is one of the most common types of corrosion in the gas fields development. The results of studying the composition of carbon dioxide corrosion products by X-ray diffraction method 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). In this case, some of the iron ions in FeCO3 can be replaced by manganese, calcium, and magnesium ions. It is shown that phases of the precipitates of non-stoichiometric composition (CaxMgyMnzFe)CO3 thus formed are poorly crystallized which is attributed to the presence of defects in the crystal structure. They will exhibit inferior protective properties compared to stoichiometric FeCO3. The film of FeCO3 is packed, uniformly distributed and tightly adhering to the steel surface. An analysis of the diffraction patterns revealed a good crystallization of FeCO3. The shape of FeCO3 particles 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.