Experimental Study On Corrosion Of X70Steel In Polluted Soil By NaOH

In indoor simulation tests, the physical, mechanical and electrochemical properties of NaOH polluted soil were studied, and the photos, microstructure images after corrosion and corrosion parameters of X70steel were analyzed. The corrosion behavior and mechanism of X70steel in polluted soil by NaOH were revealed.(1) Through measuring the physical, mechanical and electrochemical indexes in laboratory, it is found that the basic indexes of NaOH polluted soil changes as content of NaOH. Some white filaments are found on the surface of polluted soil; as the content of NaOH increases, the void ratio, air rate, compression factors and the value of pH increase, while the density, saturation, compression modulus and electric resistivity decrease; the liquid limit, plastic limit and the index of plastic limit reach the peak when the content of NaOH is1.5g/kg, and then decrease as the increasing of the content of NaOH; the water content and oxidation-reduction potential do not have the apparent regularity as the content of NaOH changing.(2) The observation of macrostructure-images and microstructure-images after corrosive, calculation of corrosion indexes and analysis of corrosion products of X70steel in NaOH polluted soil are taken out. It is found through the analysis of macrostructure-images and corrosion rate of X70steel that the extent of corrosion decreases as the content of NaOH increases.At14days, in the initial stage of the corrosion of X70steel, some black spots can be found on the microstructure-images after corrosive; At28days, in the intermediate period of the corrosion of X70steel, a small part of shallow corrosion pits emerge on the microstructure-images after corrosive; At112days, in middle and later periods of the corrosion, large areas of localized corrosion emerge on the microstructure-images after corrosive; At224days, in late period, the microstructure-images after corrosive have bigger and deeper pits of large acreage.The corrosion products of the sheet of X70steels are primarily iron, iron oxides, SiO2and silicate. The corrosion products of farinose are SiO2and silicate, and iron oxides slightly.(3) The relationship of the representative indexes of density, liquid water content, the void ratio, air rate, the value of pH, electric resistivity and oxidation-reduction potential of NaOH polluted soil and the corrosion rate of X70steel was studied. The multiple linear regression model was established. The induced variable was corrosion rate of X70steel and the independent variables were oxidation-reduction potential, electric resistivity and air rate. The inaccuracy of the measured and calculated values was found less through comparing, so it is also proved that the model can be used as the service behavior and life prediction of X70steel in the alkaline soil and underground lower oxygen content of polluted soil.