Study On Electrochemical Characteristics Of Corrosion Product Film Deposition

As the demand for energy continues to increase,the highly complex CO₂ and CO₂/H₂S oil and gas are continuously being mined.The poor corrosion damage in actual working conditions threatens the lives of people and equipment.Therefore,it is of great significance to understand and study the various corrosion processes in oil and gas fields.In this paper,N80 and 20^#steel,which are widely used at the construction site,are selected as experimental research materials.The produced liquid of XX block of a certain oil production plant in Yanchang Oilfield is used as the corrosion medium,and the surface structure and composition of the corrosion scale are treated by SEM and XRD techniques.The electrochemical characteristics of carbon steel coated with corrosion scale were studied by electrochemical method.The N80 and 20^#steel were introduced into CO₂ and CO₂/H₂S gas.Corrosion behavior of N80 and 20^#steel in different environments was revealed by the change of corrosion time,the corrosion rate of the two steel materials,the corrosion scale composition,the corrosion scale morphology and the electrochemical characteristics.The corrosion of N80 and 20^#steel by CO₂ is comprehensive corrosion.With the corrosion time prolonging the appearance of FeCO₃ and Fe in the scale layer,they can protect the matrix and reduce its corrosion rate.Under the condition of CO₂,the protective FeCO₃scale will be formed in the initial stage.Corrosion scale are continuously deposited on the surface of N80 and 20^#steel,and the outer layer is sprinkled due to severe corrosion.In the case of CO₂,the Nyquist spectrum is characterized by a single capacitive reactance arc.As the corrosion time increases,the self-corrosion potential gradually decreases and the corrosion current increases.When the current density is high,the Warburg impedance characteristic appears in the low frequency region;The slope of the MS curve of corrosion scale on N80 and20^#steel is converted from N-type to a scale having P-type semiconductor characteristics,and the scale has NP bipolar characteristics.Corrosion of N80 and 20^#steel matrix in CO₂/H₂S environment has two ways:one is pitting corrosion directly in contact with the exposed substrate at the site where the corrosion scale falls off;the Fe²⁺passes through the corrosion scale,reaching the surface of the substrate and reacting,causing the surface of the substrate to form a lamellar shedding,and the local corrosion in the H₂S-containing environment requires a longer incubation period.In the H₂S-containing environment,the scale particles formed on the surface of N80 and 20^#steel are uniformly covered.However,due to poor adhesion,some of the scale will fall off.After a period of incubation,the scale will be re-formed at the site where the scale is peeled off or cracked.A new corrosion scale;in the CO₂/H₂S existing environment,the corrosion scale particles are mainly Fe₃O₄ and Fe,covering the surface of the substrate with a large particle state at the initial stage,and the corrosion scale layer is fine with the prolongation of the corrosion time.The particle spacing becomes smaller,and the gel-like adhesion gradually forms between the particles,and the density of the corrosion scale is improved.As the corrosion time increases,the corrosion potential decreases gradually,the solution resistance R_s decreases,and the Warburg impedance appears in the reaction process at each time.When the corrosion scale on the surface of the metal substrate is continuously accumulated,the cathode reaction is not affected by the diffusion process;it indicates that the deposition of the corrosion scale during this process does not affect the corrosion process and mechanism of the sample cathode.In this case,the corrosion scale layer can reflect its protective effect on the substrate.It indicates that the porosity of the scale layer is small and dense,and ions do not easily react with the matrix through the corrosion scale.The corrosion scale formed on the surface of the two carbon steels has the characteristics of NP-type semiconductor.As the corrosion time increases,the acceptor density and the donor density of the surface-forming corrosion scale increase relatively,indicating that the resistance of the scale increases with the corrosion time.Corrosion has been reduced.