For the online detection of the corrosion of ground grids, the relationship between the corrosion rate of Q235 steel and electric resistance was studied by the method of accelerated corrosion in the soil taken from the site of construction of a 750 kV high-voltage transformer station. The corrosion products and morphology are characterized by the SEM (scanning electron microscopy) and XRD (X-ray diffraction) methods. The results show that the rusty layer obtained by the accelerated corrosion has the same structure as the layer obtained by the natural corrosion and the corrosion products mainly consist of γ - Fe2O3 and FeO4. The one-year monitoring was realized and the relationship between the corrosion rate (V ) and resistivity ( R) was established. The deviation of the natural corrosion rate from the computed corrosion rate does not exceed 3%.

Process parameters,i.e.,the current density,chromic anhydride concentration,temperature and the additive agent,were studied to solve the low currency efficiency and low deposition rate,poor lightness in chromium brush plating.The results show that the good currency efficiency and deposition rate and bright coating can be obtained when the temperature is between 25 ℃ and 28 ℃,the current density is 200 A/dm2,and the chromic anhydride is 250 g/L.As a single additive,i.e,potassium iodide,formalin,and trichloroacetic acid,can progressively improve the current efficiency,while potassium iodide and trichloroacetic acid improve the deposition rate and trichloroacetic acid,formalin and formylamine upgrade the brightness.

In the simulated DC and AC discharge circuit in ground grid protection of substation, corrosion and potential of magnesium anode with yttrium addition were studied by potential measurement and scanning electron microscopy. The results showed that potential of anode increased with increasing current density in DC simulation, potential increase of anode with 0.1% yttrium addition was the smallest, and the affordable current density of the anode reached 1.85 A/cm2, which was two times that of the anode without yttrium addition. In AC simulation, addition of yttrium had less effect on its potential. Grains of magnesium alloy sacrificial anode without yttrium addition were the equiaxed grains of magnesium grains coated with β-Mg17Al12, while the anode with yttrium was α-Mg phase with dispersed β phase. The corroded magnesium anode with 0.1% yttrium addition showed the most uniform and the smallest pit on its surface.

For the short service life of aluminium anodic oxide coating caused by ineffective sealing,the growth mechanism of coatings was analyzed.An assumption was put forward that F-and Ni2+could generate a complex compound in the micropore to ensure sealing quality.Stoichiometry,colour staining and polarization curve were employed to get the optimum sealing agent and process.The best technical condition is as follows: Ni2+content is 1.1g/L,mass ratio of Ni2+and F-is 177/228,pH value is 6,the sealing temperature is 28℃ and the sealing time is 15 min.It was found by the SEM(Scanning Electron Microscopy) that there was no nano-pore observed in the sealed anodic oxide coating.And the voltage scanning polarization in neutral NaCl solution showed its better corrosion resistance and that its passivation voltage was in the range of-1.5～0.5V.

For the fact that Brush plating of chromium is of low current effective and deposition rate,the additives to obtain the optimized prescription were studied.Twelve additives,such as KI,KIO3,acetocaustin,were respectively adapted.It was shown that KI was the most suitable additive.After doping KI to the solution at 10 g/L at room temperature,the current efficiency was raised by 46%,which was 3 times that of common brush plating,and the deposition rate reached 1 000 mg/h.When adding 8 g per liter at 60 ℃,improvement in current efficiency was 30%,and sedimentation rate at 700 mg/h could be obtained.KI is used as an catalyst but it does not deposit on the depositing coatings.

Spraying construction of high-density polyethylene was realized adopting cold spraying method.The research result of cold spraying polyethylene powder with high-density showed 180～200℃ air current temperature was the best,and coating adhesion strength can achieve 10.18MPa while temperature was 200℃,0.5mm of high-density polyethylene coating was qualified by electric spark holiday detector inspection,but there was still one pore per cm2 by blue-point inspection method.The cold application polyethylene layer is 40~60℃,NaCl and Na2S are both 3% mixed solution,the corrosion rating is less than 11mg/m2h.