Effects Of Temperature And Water Content On Soil Corrosion Behavior Of Carbon Steel At Different Exposure Time

Few researches were made on the corrosion behaviors of metal in soils with different water contents at high temperatures. As many pipelines are buried in soils with high water contents at high temperatures, it was necessary to make the researches on the corrosion mechanisms of carbon steel in soils with different water contents at different temperatures. In this thesis, the corrosion behavior of 20# carbon steel in soils with different water contents at different temperatures was studied in the time course of corrosion by means of macro-morphology observation,weight loss and some electrochemical test techniques, such as polarization curve and electrochemical impedance spectroscopy (EIS), etc.The results revealed that corrosion products were different in soils with different water contents. In our work, locally corroded surfaces were observed in soils with low water contents, while evenly corroded surfaces were founded in soils with high water contents, and corrosion of carbon steel became more serious with increasing of temperature and exposure time.By analyzing the curves of corrosion potential in soil vs. time, it is found that water content was a more prominent factor than temperature. The corrosion potential of carbon steel was more positive in soils with lower water content. And the results of weight loss showed that the corrosion rate of carbon steel gradually increased along with the decrease of water contents in soil and along with the increase of temperature. Furthermore, the effects of exposure time on the corrosion of carbon steel were dependent on temperature and water content in soils. And the corrosion was more sensitive to the temperature in soils with lower water content.From the obtained polarization curves, we could find that polarization curves moved to right with increasing temperature, that was, corrosion rate was speeded up. Marked anodic diffusion control was not observed in soils with various water contents, while corrosion of carbon steel in the soil with higher water content was controlled by the cathodic diffusion process. And this diffusion process became obviously with decrease of water content and temperature, also with development of corrosion. And polarization curves also confirmed that the corrosion was more sensitive to the temperature in soils with lower water content and development of corrosion.Based on the characteristics of EIS of carbon steel in soil, it was found that reactions were affected by water content of soil, temperature and exposure time, while corrosion products were affected only by water content of soils. The EIS results also showed that polarized impedance decreased with increase of water content and temperature. The effect of exposure time on transmission impedance was dependent on temperature and water content in soils.