Research On Evaluation Methods For Soil Corrosiveness Of Substation Grounding Grid

Total 26 substations were excavated and sampled in east China.Physical and chemical properties of each soil sample were measured and the key influence factors were selected by Factor analysis to make a comprehensive evaluation. Accelerated corrosion experiments of Q235 and galvanized Q235 steel in soil sampled from 15 substations were made by the control of soil temperature and water content. Weight-loss and microscopic characterization of grounding grid and specimens indoor were studied to evaluate the correlation between substation and experiment indoor. A new platform for study on soil corrosion may be provided by the device. Characterization of grounding grid in different pH values and water contents and SO42- and Cl- were studied in red soil, a reference for corrosion protection of grounding grid was provided for this region.(1) Key factors were selected by factor analysis method (including pH, moisture content, SO42-, HCO3- and Ca2-++Mg2-), a comprehensive evaluation was made by the key factors on the soil corrosivenees of substations, which simplifies the evaluation system and maintains the the results same with the excavation.(2) Corroison of substation grounding grids in 15 substation soils was accelerated with the soil temperature controlled at 60℃ and the water content of each soil maintained the same with initial water content. The result shows that the correlation between experiment indoor and substation is good.(3) The XRD of grounding grid and specimens indoor shows that iron oxide products of grounding grid mainly consist of Fe2O3 and FesO4 and FeOOH, zinc oxide produts mainly consist of ZnO and Zn4(CO3)(OH)6. Iron oxide products of specimens indoor mainly consist of Fe2O3 and Fe3O4 and FeOOH, zinc oxide produts of galvanized Q235 mainly consist of ZnO, zinc oxide produt of some specimens is Zn4(CO3)(OH)6. The SEM and EDS analysis of specimens indoor shows that most of the products have S expect Fe and 0 and Zn, some of the products have Cl, which is consistent with the result of grounding grid. The corrosion mechanism of galvanized Q235 steel was not changed in the accelerated experiment.(4) With the increase of water content, corrosion rate of galvanized Q235 steel shows a trend of increase at first and then decrease and reaches the max value when the water content is 20%. With the increase of pH value, corrosion rate of galvanized Q235 steel shows a trend of decrease at first and then increase and reaches the minimum value when the pH is 8.(5) With the increase of SO42- content, corrosion rate of galvanized Q235 steel shows a trend of increase at first and then decrease and with the increase of Cl- content, corrosion rate of galvanized Q235 steel shows a trend of increase at first and then maintain stable. But, near the peak of corrosion rate one copy of SO42- have the same contribution to soil corrosiveness with two copies of Cl-, which has grest meaning to the develop of resistance reducing agent.