The Corrosion Behavior Of Grounding Material In Red Soil System

The southern red soil as the experimental study on the corrosion medium system was used. The corrosion behavior of stainless steel clad steel in acid red soil was studied by electrochemical experiments and surface analysis technology. The corrosion resistance of four kinds grounding materials of copper, 304 stainless steel, galvanized steel, carbon steel was compared in red soil. The corrosion resistance of the weld metal and the parent metal, and the galvanic corrosion situation of different anions and area ratio of 304 stainless steel and Q235 carbon steel couple of stainless steel clad steel cross section in the red soil were studied. Using potentiodynamic polarization and circular polarization method evaluate the 304 stainless steel rapidly by adding several common ions in the red soils.Contents and conclusions were as follows:(1) In the saturated water red soil system(water content of 31.04%), with the extension of soaking time the grounding material of 304 stainless steel has good corrosion resistance all time, and its impedance value Z0.05 has remained at about 60 kΩ?cm2 after soaking 45 d. The impedance value of copper grounding material increases gradually with the increase of immersion time. The galvanized steel has smaller resistance value in the early immersion time; with the increasing of immersion time the surface gradually has formed a layer of corrosion product film which prevents its further corrosion. Carbon steel has the lowest corrosion resistance and the most serious corrosion. From the impedance of the materials value can be seen, stainless steel>copper>galvanized steel>carbon steel from the corrosion resistance. Materials of confocal optical microscopy images show that stainless steel, copper after 45 days immersion still can be seen obvious scratches, maintained before soaking polished morphology; and carbon steel, zinc coated steel electrode surface is uneven, which has many corrosion pits.(2) Manual welding and hot melt welding methods have increased the relative content of Ni and Cr elements which has seen from the EDS spectra. Electrochemical impedance spectroscopy showed that the manual welding impedance is more close to the 304 stainless steel base material, which better than the hot melt welding. Polarization curves showed that the corrosion current density and the corrosion potential value was basically the same of the weld area of manual welding and 304 stainless steel base metals. Hot melt welding corrosion potential is higher than base metal, and the corrosion current density is larger, which is consistent with the electrochemical impedance results.(3) Stainless steel clad steel exposed cross section exist galvanic corrosion when under the saturated soil. Results show that the formation of the galvanic couple by the 304 stainless steel and the Q235 carbon steel accelerate the corrosion of the anodic metal. With the increase of galvanic couple area ratio of cathode and anode, the galvanic current increases gradually and the same to the galvanic potential. As can be seen from the impedance values of galvanic, cathode and anode area ratio is larger, the smaller the value of electrochemical impedance is. The stainless steel did not corrode basically after soaking for 45 d, but the carbon steel was extremely serious corrosion in an all-round way. Corrosion in stainless steel and carbon steel joint is the most serious. The corrosion products are mainly iron oxides.(4) The 304 stainless steel has good corrosion resistance. In the red soil solution was added in SO42-, the impedance value of 304 stainless steel is increased and its cyclic polarization curves don’t appear obvious hysteresis loop, there is no pitting. Under the condition that containing Fe3+ and SO42- ions at the same time, the impedance increases first, then decreases with the increase of Fe3+ concentration gradually decreased, but still does not appear hysteresis loop. But in soil systems with Fe3+ and Cl- ions, cyclic polarization curves show obvious hysteresis loop, there is severe pitting corrosion, and with the increase of Cl- concentration, hysteresis area increased gradually.(5) In the application of the 304 stainless steel clad steel for grounding materials in the construction process, should be used low Fe3+, Cl- content of soil burial, and pay attention to the stainless steel clad steel bare cross section protection to prevent the galvanic corrosion occurring.