Study Of Corrosion And Protection For Grounding Steel In Hign-resistivity Soil

With the development of electric power industry, the installed capacity of the power generation will reach a great level than now. The safe operation of the grid is increasingly strict. As the important part of transmission&transformation facilities, the corrosion of grounding grid would cause accidents that endangering the stability of the power grid, the problem is becoming the spotlight. As the vital part of Western Development, the corrosion and protection of the substation grounding grid in Ningxia region has already aroused people’s attention.The purpose of this study was to investigate the influence of Cl-and SO42-and moisture on the corrosion behavior of grounding steel20G, Q235steel, and galvanized steel. The corrosion rate and the performances of electrochemistry were assessed by soil buried and electrochemical experiments. The corrosion products were examined by scanning electron microscope(SEM), energy disperse spectroscopy(EDS), and X-ray diffraction(XRD), and discussed the corrosion mechanism. On the basis of soil physics and chemistry performance of Ningxia, the protection schemes for20steel and galvanized steel are designed. The research results not only provided the theoretical support for studying corrosion of grounding steel in the region, at the same time as the references for the cathodic protection of grounding steel.The main conclusions were as follows:(1) Cl-accelerated the corrosion of20G and Q235steel and galvanized steel, and the corrosion resistance of galvanized steel was better than20G and Q235steel. With the increase of Cl-concentration, the corrosion rate of20G and Q235steel increased first and reached a peak value, then decreased. Corrosion rate of galvanized steel increased as the Cl-concentration, but when the concentration of Cl-reached2.5percent, the trend slow down.(2) The corrosion resistance for SO42-of20G and Q235steel was less than galvanized steel. The corrosion rate of galvanized steel increased at first then decreased, when SO42-concentration is1.5percent, the value reached the maximum. When SO42-concentration was at the range of0.5to1.0percent, the growth range of corrosion rate was largest.(3) The moisture had great influence on the corrosion of20G and Q235steel and galvanized steel, and for both grounding steels, the corrosion rate had a peak value at one moisture level. At the same water content, the corrosion resistance of galvanized steel was superior to20G.(4) From analyzing of corrosion morphology and products, Cl-and SO42-involved in the corrosion reactions as catalyst for20G and Q235steel, but for galvanized steel, the two ions induced the hydrolysis of zinc layer. The moisture influenced the transfer of oxygen in the process of reaction.(5) Designed the scheme of cathodic protection on the basis of soil physics and chemistry performances, and then indoor simulation experiment was conducted. The results showed that the designed sacrificial anode cathodic protection system for high soil resistivity in Ningxia area can play an effective protection. The protective potential of galvanized steel and20G fluctuated in the range of300mV, and the protective degrees were over97percent. The both parameters showed that the all system run stably.