| The properties of physical, mechanics and electrochemistry of soil polluted by NaCl and Na2SO4were statistically studied from indoor simulation test. The multiple linear regression equations of X70steel corrosive rate about two pol-luted soils were established to describe the relationship between the corrosion rate of X70steel in polluted soil and the corrosive parameters of the soil. The corrosive behavior and mechanism of X70steel in soil polluted by NaCl and Na2SO4were also analyzed. The conclusion will be useful for guidance of se-lecting and defending of steel material in sites of contaminated soil.Firstly, laws of change of the main physical mechanics and electrochemi-stry parameters of the polluted soils with the content of NaCl and Na2SO4were studied. The saturation and density increase, while the liquid limit, plastic limit and plasticity index decrease with the content increasing of NaCl and Na2SO4. Meanwhile the water content, compressibility coefficient and modulus of com-pressibility also change, but varieties are not obvious.Electrical resistivity, redox potential decrease, while the corrosion poten-tial increase as the content of NaCl and Na2SO4increasing. The corrosive para-meters comparisons were caculated on standard deviation, coefficient of varia-tion and confidence interval between the two kinds of soil, showing that NaCl and Na2SO4have significant influence on electrical resistivity, while having lit-tle effect on water content, saturation, density, redox potential and corrosion po-tential.Secondly, the distinction of impact of NaCl and Na2SO4on the polluted soil was studied. It concluded that NaCl has greater influence on saturation, density and electrical resistivity than Na2SO4, and Na2SO4has greater influence on in-dex of plasticity, redox potential and corrosion potential than NaCl, but NaCl’ corrosion is greater than Na2S04when both the content is equal at the evaluation steel corrosion based the current corrosive evaluated code.Thirdly, the macro and micro images of X70steel samples were analyzed during the corrosion procedure. At the beginning period of the corrosion proce-dure, corrosion begins partly in area. Some corrosion pits appeare on the surface of the X70steel samples. As time went on, corrosion pits become much larger and deeper, and the corrosion products increase continuously. The corrosion is much more obvious in the soils with higher content of NaCl and Na2SO4. The corrosion pits of samples in soil polluted by NaCl are deeper than that in soil polluted by Na2SO4. The samples in soil polluted by Na2SO4have more corro-sion pits than that in soil polluted by NaCl.Fourthly, corrosion weight loss and corrosion rate were calculated and cor-rosion dynamic equations were establised. The result shows that corrosion weight loss and corrosion rate become lager as the content of NaCl and Na2SO4grows up. The corrosion weight loss increase, while corrosion rate decrease with time increasing. As a whole, the corrosion weight loss and corrosion rate of X70steel in soil polluted by Na2SO4are larger than NaCl. The values of parameters of corrosion dynamic equation and corrosion influence factors of X70steel in the two kinds of polluted soil were obtained.Fifthly, the corrosion product of X70steel samples in the polluted soil was analyzed by using X-Ray Diffraction(XRD) and the corrosion mechanism is analyzed by chemical equation. In NaCl polluted soil, the main corrosion prod-uct of X70steel samples is FeOOH, and there is a few ferriferous oxide, while in the soil polluted by Na2SO4, the main corrosion product is Fe2O3, with some Fe3O4, FeOOH. The effection of the properties of polluted soils to corrosion rate of X70steel was analyzed. Two corrosive rate of X70steel multiple linear re- gression equations were established based on the relationship between the cor-rosion rate of X70steel in polluted soil and the corrosion parameters of the soil. It is proved that the equations could be used for predicting the working period of X70steel in soil polluted by NaCl and Na2SO4. |
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