Researches On Corrosion Electrochemical Behaviour Of Gathering Pipeline Steel In Oil And Gas Field Containing CO₂

Owning to the corrosive gas as CO₂ contained in the oilfield wastewater, the well pipelines, equipment and gathering pipelines encounter serious corrosion perforation damage. In this paper, we hope to have certain guiding significance to safety production of oil and gas field, through the study of electrochemical corrosion behavior and local corrosion of the pipeline steel in the oil and gas environment with carbon dioxide. In order to carry out this experiment, we design a device, which can be injected two kinds of corrosive gases, carbon dioxide and hydrogen sulfide to the simulated solution of the produced liquid with ensuring the safety.and we use the polarization curves, electrochemical impedance spectroscopy and scanning electron microscope test to carry out the study of electrochemical corrosion behavior and local corrosion of 20# steel in the product liquid of oil fields with carbon dioxide, and the features of local corrosion of pipeline steel in the gas fields containing CO₂ condensate water.The results show that:1) In a way, the increasing of the concentration of carbon dioxide can reduce the rate of general corrosion of 20# steel; the corrosion product films of 20# steel under the condition of low concentration of carbon dioxide is mainly due to carbon dioxide but with no much influence of the concentration of H₂S; when under the condition of high concentration of carbon dioxide, carbon dioxide has little contribution to the corrosion product film, it mainly depends on the concentration of hydrogen sulfide.2) The typical characteristics of gathering pipeline steel in oilfield fluid containing carbon dioxide are localized pitting corrosion, round moss corrosion, mesa of corrosion. The main components of the corrosion product film are Fe2O3 and FeCO3; The presence of chloride ions can destroy the oxide layer on the surface of the carbon steel materials and induce local pitting.3) Compared with 25 ℃, the local corrosion situation of wire beam electrode in condensate water containing CO₂ by 40℃, the corrosion rate of activity center and the surrounding are very different. This shows that the rise of temperature increased the tendency of local corrosion occurred and strength.