Research On Corrosivity Of Atmospheric Environment And Corrosion Grade Mapin Guangxi

In this paper,outdoor air exposure tests of Q235 carbon steel and pure zinc plate samples were carried out at 42 stations in Guangxi.At the same time,pollutant factors which were sulfate deposition rate and chloride ion deposition rate were monitored at 21of 42 sites mentioned above.The experiment has been carried out for three cycles which lasted for 3,6 and 12 months.4 typical stations of 42 stations were selected:Liubei Station in Liuzhou City,Haijiao Station in Beihai City,Huangma Station in Qinzhou City and Xinxing Station in Fangchenggang City.The corrosion rate,macro and micro morphology,composition of surface corrosion products and electrochemical impedance analysis of the above two materials were carried out at four stations in Guangxi.At the same time,different kinds of indoor accelerated tests are carried out on pure zinc plate and galvanized steel to find a rapid detection method for metal materials used in power transmission and transformation network.Based on the average annual pollutant data,combined with the meteorological factors of annual average rainfall,temperature and humidity in Guangxi and the corrosion rate of carbon steel and pure zinc plate in 42stations over the years,the corrosion rate of the above two materials in each station was predicted by feedforward neural network in the toolbox of MATLAB neural network.At the same time,the spatial interpolation of meteorological and pollutant data is carried out,and the above spatial interpolation data are predicted by using the established neural network,and the atmospheric corrosion grade distribution maps of Q235 carbon steel and pure zinc in Guangzhou are drawn.The main results are as follows:（1）According to the outdoor exposure test results of corrosion rate and pollutant factors at four different stations in Liubei,Haijiao,Huangma and Xinxing,the corrosion rate of carbon steel and zinc plate in Liubei station with high concentration of SO₂and Cl^-pollutants in the atmosphere is the highest.The corrosion products of carbon steel in four sites are mainlyα-Fe O（OH）,γ-Fe O（OH）and a small amount ofβ-Fe O（OH）.With the increase of time,the more stable substance Fe₃O₄was found on outdoor exposed samples for 12 months,and Fe SO₄·n H₂O could be found in Liubei station.Through the analysis of corrosion products and environmental factors,it is found that Cl^-can promote the formation ofβ-Fe O（OH）,but the high concentration of SO₂pollutants in the atmosphere can inhibit the formation of this substance to a certain extent.The main corrosion products of zinc sheets at four sites are Zn（OH）₂,Zn₅（CO₃）₂（OH）₆,Zn₅（OH）₈Cl₂·H₂O and Zn SO₄·n H₂O,which have good protective effect on the matrix.The results of electrochemical impedance spectroscopy（EIS）test show that the Rt of zinc plate specimens increases with time,which indicates that the corrosion products on the surface of zinc plate have obvious protective effect.This phenomenon is not obvious for carbon steel specimens.But it can be found that the corrosion product capacitance Qr of carbon steel specimens at Liubei Station for 6 months is much higher than that of other periods,which indicates that there are many defects in the rust layer in this period.（2）Through different kinds of indoor accelerated tests,it is found that the corrosion rate of zinc plate and galvanized steel is higher in neutral salt spray test,dry-wet cycle accelerated test and compound accelerated cycle test,but lower in wet-hot test and sulfur dioxide corrosion test.The results show that the effect of sulfur dioxide on atmospheric corrosion of zinc is not obvious,but the effect of sulfur dioxide combined with high humidity and Cl^-on atmospheric corrosion of zinc is greater.The corrosion resistance of galvanized steel can be rapidly evaluated in a short time by using the compound cycle accelerated test method of three-day sulphur dioxide test and three-day cycle accelerated test containing salt spray for 1 h,drying for 2 h,and humidity and heat for 1 h.（3）The feed forward net model is used to predict the annual corrosion rate of 42stations in Guangxi.It is found that the feed forward net model has a good prediction accuracy for the early corrosion rate of carbon steel and zinc plate in Guangxi with complex meteorological factors.According to the weight values of each factor of the feedforward neural network,the sulfate deposition rate is the main factor affecting the corrosion of carbon steel and rainfall and humidity are the main factors affecting the corrosion of zinc plate.The corrosion rate of carbon steel in industrial polluted areas such as Liubei is the highest,and that of zinc plate in some coastal areas is the highest.