Corrosion Behavior Of Substation Grounding Material In Simulated Soil

The grounding grids are important devices in substation, and they are widely used to prevent lightning, electrostatic and fault current. In China, the grounding grids are mainly composed of iron and steel materials. They will be tend to thinner or even corrosion fracture due to the electrochemical corrosion in the soil. Therefore, the soil corrosion of ground grids is one of the most important practical corrosion problems. However, buried sample outdoor method, simulated soil solution method and soil saturated solution method and so on, they are the usual methods of researching the grounding grids’corrosion behaviors in the soil. There are many characteristics of these methods, such as long period, costing resources, corrosion process or corrosion mechanism likely to be different from soil corrosion. Therefore, it is particularly important to establish a method of fast evaluating grounding grid materials’soil corrosion resistance which can be applied to different physical and chemical properties of soil.In this article, we use the acidic soil in southern as an reference and adopt indoor accelerated corrosion testing in simulated acidic soil environment which was prepared using diatomite. The physical and chemical properties of soil such as porosity, moisture content, salt content, pH value on the material of Q235steel corrosion law were studied by means of physical and chemical phase analysis, scanning electron microscopy, electrochemical workstation and laser Raman spectroscopy. In addition, we compared the corrosion behaviors of Q235steel and X65steel in simulated soil. The reason of different corrosion laws and rate on Q235steel and low alloy1Cr steel in simulated soil were also discussed. The conclusions are as follows.The soil porosity, moisture content, salt content, pH value of simulated soil have different impacts on corrosion behaviors of Q235steel. The corrosion rate of Q235steel increased gradually with fine diatomite in simulated soil ratio increased, When the moisture was30%, there were a largest corrosion rate of Q235steel. In this research, there was not many differences on the corrosion rate with the change on the salt content, also the corrosion rate of Q235steel decreased with the pH value of simulated soil increased.The testing of Q235steel and X65steel buried in simulated soil and real soil the two corrosion environment mediums for a month showed that each material in two kinds of soil environment presented similar corrosion behaviors. Both of their corrosion morphologies were from pitting develop to general corrosion, and the corrosion rate had a certain regularity. The anode active controlled electrochemical polarization behaviors and the corrosion potential occurred positive shift. Also the corrosion products were mainly composed of α-FeOOH、Fe3O4、Fe2O3. At the same time, compared with the real soil corrosion environment, two materials’corrosion rate in simulated soil environment with acceleration, about2～3times as much, the rust layers were thicker, more dense and not easy to fall off. There were good reproducibility in corrosion situations between each sample.It could be distinguish the resistance to acid soil corrosion ability between Q235steel and1Cr steel in simulated soil. The Q235steel had relatively poor corrosion resistance, the corrosion rate can be up to0.68mm/a, which was about2times than1Cr steel. With the extension of corrosion cycle, the rust layers also appeared separated layer.1Cr steel had dense rust layers, not fell off easily, while rust layers of Q235steel were loose and bad protection.