Assessment of the Influence of Glycol and Alcohol on the Morphology and Protective Properties of Iron Carbonate in Carbon Dioxide Corrosion of Gas Pipelines

Abstract—The potential influence of hydrate formation inhibitors (glycols, alcohols)—components of the liquid phase of gas pipeline operating media—on carbon dioxide corrosion during the transport of aggressive gas has been insufficiently studied. The results of a study of the corrosive effect of glycol (alcohol) being present in the liquid phase on the composition and properties of corrosion products on steel when simulating the main aggressive factors under conditions of transport of CO2-containing gas are presented. The aggressive conditions of variable wetting of the walls of a gas pipeline with water are reproduced on a corrosion test stand. The liquid circulation characteristic of a partially filled pipeline can have an effect on preventing the formation or destruction of films of corrosion products (iron carbonate, siderite) on the steel surface. In places of cracking and peeling of siderite, which forms in the presence of CO2, conditions will arise for the formation of total and local corrosion damage. In the simulation tests, mono-ethylene glycol and isopropanol, as well as their aqueous solutions of different concentrations, are used. For the first time, data on the formation and composition of nonstoichiometric siderite in the aqueous–glycolic and aqueous–alcoholic media at different CO2 partial pressures and temperature are obtained. Using X-ray diffraction, by processing the obtained diffraction patterns, the degree of substitution of iron ions with other cations in nonstoichiometric siderites is determined. The dependence of the degree of substitution on the concentration of alcohol (glycol) in their aqueous solutions is analyzed. It was revealed that with an increase in the concentration of glycol, a decrease in the rate of local corrosion is observed. At high glycol content, complete suppression of internal corrosion in the presence of CO2 occurs. It is established that in the aqueous–alcoholic media, at elevated temperatures, local carbon dioxide corrosion does not proceed. This is apparently due to the uneven distribution of water and alcohol in the mixture. The results can be used in assessing internal carbon dioxide corrosion in the presence of glycol (alcohol) used at gas facilities as an inhibitor of hydrate formation.