Study on the Corrosion Behavior of Q345B Steel as Grounding Electrode Material in UHVDC System Based on Electrochemical and Immersion Experiment

The corrosion caused by direct current was the main factor to result in the failure of grounding electrode in UHVDC (ultra-high voltage direct current) system. Compared with the severe corrosion caused by thousands of amperes flowing from the grounding electrode during the system failure, the corrosion of grounding electrode caused by electric field formed by the unbalanced current can not be ignored in normal operation, but there were little relevant reports and studies focusing on this condition. In this paper, the corrosion behavior of Q345B steel as grounding electrode material was studied under different direct current density of 0-1.5 A/cm(2) based on the electrochemical experiment and immersion experiment. The results showed that with the increase of direct current density (I-DC), the corrosion potential (E-corr), corrosion current density (I-corr), corrosion rate and maximum pit depth showed the linear changing rules, namely E-corr=-0.0568 center dot I-DC-0.7338 (R-2=0.8784), I-corr=33.69 center dot I(DC)4.3406 (R-2=0.9649), corrosion rate = 0.0648 center dot I-DC+0.0047 (R-2=0.9952) and maximum pit depth = 80.032 center dot I-DC+83.946 (R-2=0.9554), respectivly. The coverage rate of corrosion products on the surface of Q345B steel gradually decreased, and the corrosion products changed from polygon to triangle, which can be described as Fe2O3 (FeO(OH)-> Fe2O3+H2O), FeO(OH) (4Fe+3O(2)+2H(2)O -> 4FeO(OH)) and FeCO3 (Fe+HCO3--> FeCO3+H++2e(-)).