Study On The Corrosion Problems In Application Of Grounding Grid Of 304 Stainless Steel Cald In Substation

Grounding grid is an important device to make sure safe and stable operation of the power system.New 304 stainless steel cald,metallurgical combination prepared,possesses good electrical conductivity,combination,thermal stability and corrosion resistance,which is expected to become a new generation of grounding material to solve the problem of poor corrosion of grounding material.However,there are many unresolved issues of 304 stainless steel cald in practical engineering applications,such as surface cleaning,corrosion resistance of welded joints and large current impuluse etc.,which limit its engineering applications.This paper studies a cleaning agent which is suitable for removing the oxide of stainless steel cald grounding grid,corrosion rules and anti-corrosion measures of the weld zone by electrochemical experiments and electrolysis accelerated corrosion and variations of microstructure and properties of 304 stainless steel clad after high current impulse,which provide theoretical and experimental basis for engineering applications of 304 stainless steel clad groungding grid.The results show that:(1)Preferred amount of the additives are studied for scavenging surface oxide of stainless steel clad steel.Sodium fluoride promotes the dissolution of the oxide scale,increasing the pickling efficiency,and the preferred mass is about 0.075-0.125 g/ml.Magnesium nitratepromotes the formation of a passivation to protect the substrate during the pickling process;The picklied surface is smooth after citric acid pickling.But both of them slow the pickling rate,whose preferred added mass are 0.05-0.15 g/ml and 0.025-0.075 g/ml,respectively.(2)The optimized pickling recipe for 304 stainless steel clad steel by orthogonal experimental method is:volume concentration of nitric acid being 0.2 ml/ml,volume concentration of sulfuric acid being 0.1 ml/ml,mass concentration of sodium fluoride being 0.075 g/ml,mass concentration of magnesium nitrate being 0.075 g/ml,mass concentration of citric acid being 0.025 g/ml,the remainder being deionized water.Surface oxide of stainless steel clad steel is completely dissolved,surface bright,grounding resistance meeting the design requirements.after picklied 10 min.(3)Corrosion rate of the weldis of stainless steel cald maximum at 25%moisture content,2.1%Cl-and 5.76-%SO42-of the soil environment of grounding grid buried.The corrosion rate decreases firstly and then increases with the increasing of pH from 3 to 11.The corrosion rate is minimum in weak acid and alkali and increases rapidly in strong acid and alkali.(4)The corrosion rate of stainless steel weld is much greater than the base material in Fujian Sanming soil environment.Thus,the weld must be embalmed in order to reduce corrosion of the weld.(5)The resistivity of new 304 stainless steelcald changes little and cladding is intact and unruptured after three high current impulse.Tensile strength of 304 stainless steel cald stick impulsed is greater than the non-impulsed.Corrosion resistance of the cladding of 304 stainless steel is reduced and corrosion resistance of the weld is essentially same.(6)Pearlites of Q235 matrix appear refined and are weakly dispersed at the grain boundaries after high current impulse.The grain size of different regions of 304 stainless steel cladding changes largely and pitting corrosion prones to occur.Grain of weld zone is essentially the same and the corrosion resistance is essentially unchanged.