Research On Corrosion Effect Of Ac Stray Current On Q235 Steel In Alkaline Soil Simulated Solution

The grounding grid is the key equipment for substation discharge,elimination of operating current and prevention of lightning surge accidents.The AC substation grounding grid is disturbed by stray current which possesses variable voltage and frequency,such as discharge voltage,induced electric field currentand operating current.In addition,the moisture contentand pH of soil have a great impact on corrosion rate of the grounding grid.Many kinds of influencing factors make the research on AC stray current corrosion not deeper,the current stray current theory cannot guide protection of the substation grounding network,and therefore,this article systematically explores AC stray current corrosion.In order to eliminate the interference of soil corrosion factors,triangular wave alternating current was used as stray power source,and alkaline soil simulation solution was used as corrosion medium in the research process.In order to provide reference for underground corrosion protection irn alternating electric field,the AC electrochemical corrosion process and law of Q235 steel under different AC voltage and frequency disturbances were studied by means of enhanced dielectric,electrochemical analysis,corrosion weight loss and morphology analysis.The results of the research show:(1)Under AC interference,the polarization curves of the anode and cathode were not completely coincidentwhen the potential rise and fell.The corrosion potential EC of Q235 steel was split into:a high potential and a low potential,and this two potential changed regularly with the changes of AC voltage and frequency.In the strong AC field,the Q235 steel was passivated in the alkaline corrosion medium,and the passivation film was broken,a large amount of hydrogen was precipitated in cathode processwhen the positive potential is high,then the hydrogen corrosion of the grounding network occured.(2)When the AC voltage was lower than 1.5V,Q235 steel was less corroded,which belongs to even corrosion.When the AC voltage was higher than 1.5V,the corrosion of Q235 steel was accelerated and pitting corrosion occured,which increases the harmfulness.The corrosion rate of Q235 steel increased first and then decreased with the increase of AC frequency,and the corrosion rate had a maximum value.(3)The effect of frequency on corrosion mechanism is different with different AC voltage.When the AC voltage was low(example AC voltage 0.3V),when the frequency was lower,the corrosion of Q235 steel was Local corrosion.On the contrary,when the frequency was higher,the corrosion of Q235 steel was uniform corrosion.When the AC voltage was higher(example AC voltage 1.0V or 2.5V)and there are three frequency values corresponding to the local corrosion of Q235 steel which is the lightest,the most serious local corrosion,the first serious uniform corrosion and then the pitting corrosion.(4)When the AC voltage was low,HCO3-/NO3-slowed down the corrosion of Q235 steel and SO42-/Cl-erosion could be ignored.When the AC voltage was high,SO42-and Cl-promoted the passivation film breakdown,hindered the passivation film re-deposition.SO42-/Cl-reduced the amount of dissolved oxygen in the corrosive medium and HCO3-promoted hydrogen evolution.