Analysis of the influence of aggressive factors and conditions on the composition of corrosive products

Abstract

Data on the use of the X-ray diffraction method in the analysis of the composition of corrosion products are presented. Such knowledge makes it possible to obtain information on the mechanisms of corrosion development and the protective properties of corrosion products, being either dense (with certain protective properties against corrosion) or loose (with a low level of protection against corrosion), which doesn't prevent the penetration of corrosive media to steel surfaces. Under H2S conditions, a layer of mackinawite (tetragonal FeS) is formed on the surface of steels, and in acidic environments of formation water imitations, it was found that, in addition to it, cubic FeS is formed. Iron sulfide with a cubic crystal structure, being metastable, reduces the protective properties of the sulfide film in aggressive acidic H2S media. During carbon dioxide corrosion of steel, the main product is siderite (FeCO3), characterized by the phenomenon of isomorphism (i.e. changes in the chemical composition of the phase while maintaining its crystal structure). It is established that in the formation water model, sediments of non-stoichiometric composition CaxFeyCO3 and (XFe)CO3 are formed, where X = (Са2+, Mg2+, Mn2+). Both of them are poorly crystallized and have defects in the crystal structure, which reduce their protective properties relative to the stoichiometric FeCO3 formed in a 3%NaCl solution. A corrosion inhibitor in aqueous media promotes the adsorption of the inhibitor film, preventing the formation of corrosion products.