Effect Of Increasing CO₂ In Atmosphere On Atmospheric Corrosion Of Metals

The dissertation is a partial study of the project (59871051) supported by the National Natural Science Foundation of China, and a sub-project of international cooperation between Royal Institute of Technology (Sweden) and Institute of Corrosion and Protection of Metals, Chinese Academy of Sciences.A series of studies about effect of increasing CO₂ in atmosphere on metals (Zn,UNS G10190) were carried out in laboratory. In addition, according to demands of exploitation of TARIM Oil Field, field test in desert oil field and simulating test in lab were carried out. Some new results were derived from experiments. They are as follows:1) The kinetics of atmospheric corrosion of zinc under thin electrolyte film.Quartz crystal microbalance(QCM) has been used to study the kinetics of atmospheric corrosion of zinc in air containing different concentrations of carbon dioxide at 85%RH and 25℃.The kinetic equation indicated that the corrosion rate of zinc under thin electrolyte film is directly proportional to the power of the time of wetness(t): R= ktⁿ. The physical significance of the parameters in the equation was elucidated. Combined with IR, XEDS and SEM , it has been found that the corrosion product of zinc exposed to 85%RH atmosphere containing CO₂ is hydrozincite. If the concentration of CO₂ in atmosphere is less than 0.04%(v/v), the corrosion product has protective feature. Otherwise, the corrosion product has no protective feature. At the same time, atmospheric corrosion mechanism of zinc under thin electrolyte film is discussed.The former result was verified that the original corrosion product of zinc under thin electrolyte film will continue to transform into secondary corrosion product , and the secondary reaction began after 15 hours when zinc is covered by the thin electrolyte film. 2) Synergistic effect of NaCl and CO₂ on atmospheric corrosion of zinc under thin electrolyte filmBased on QCM measurements, it was found that carbon dioxide slowed down the corrosion rate of zinc in the presence of NaCl. This is explained by the neutralization of surface electrolyte resulting in the precipitation of chloride in the form of insoluble Zn₅(OH)₈Cl₂·H₂O. It is referred as synergistic effect of NaCl and CO₂ on atmospheric corrosion of zinc under thin electrolyte film.3)Effect of marine and industrial atmospheric environments on corrosion of metal ZnEffect of marine and industrial atmospheric environments on corrosion of metal Zn is studied for the first time using QCM, combined with IR. QCM results show that NaCl deposited on surface of zinc is the one of most corrosive electrolytes among studied electrolytes to atmospheric corrosion of zinc. The second is (NH₄)₂SO₄ deposited on the surface of zinc, and the slightest is Na₂CO₃. Combined with the IR analysis of the corrosion products, the mechanism of corrosion under thin liquid film is elaborated.4) Effect of CO₂ in atmospheric on atmospheric corrosion of UNS G10190The atmospheric corrosion of UNS G10190 steel by CO₂ has been studied in the laboratory by electrochemical technique, combined with observation of the surface by XRD and SEM. The results of electrochemical experiments indicated that the corrosion rate of UNS G10190 increased with increasing CO₂ concentration. Results taken from XRD and SEM show that there is no carbonate in corrosion product on the surface of UNS G10190 steel. Corrosion product can be formed in two layers: inner layer and outer layer of corrosion product. From experimental results it is concluded that CO₂ plays an enhancing role in atmospheric corrosion of UNS G10190 steel. The film of corrosion product is slightly protective.4) Corrosion behavior of API N80 in high salinity brine containing CO₂By the study of effect of CO₂ in high salinity brine on API N80, both in TARIM Oil Field and in laboratory, the experiment results show that the corrosion rate of API N80 increased with the partial pressure of CO₂. In the circumstance, there is an empirical relationship between the corrosion rate (V_c, mm/a) and the partial pressure of CO₂ (PCO₂, MPa) lgV_c = 1.01×lgP_CO2 - 0.41 5) Prediction on the scaling tendency of water injection system in Lunnan, TARIM Oil FieldThe tendencies to form carbonate and sulfate scales in different sections of the water injection systems of Lunnan, TARIM Oil Field Complex, are predicted by using Stiff-Davis' saturation indexes and Skillman's solubility parameter as criteria, respectively, and the tolerances of the injection water to Ba²⁺ and Sr²⁺ at different temperatures are calculated. Simulation experiments in autoclave are performed on a laboratory installation and the scale layer on the metal sample is analyzed by X-ray diffraction. It is shown that CaCO3 scale will deposit slightly and must be properly inhibited; no CaSO₄ scale will be formed; and (Ba, Sr)SO4 scale appears if Ba²⁺ and Sr²⁺ exist in injection water.