The Evaluation Of Atmospheric Corrosivity Category And Corrosion Behavior Analysis Among China Southern Power Grid Region-Guangdong Province

With the rapid development of economic,power supply is increasingly busy and the number of transmission towers is surging.As a critical infrastructure in power industry,the atmospheric corrosion of transmission towers directly affects the safe and efficient operation of power supply network.In order to ensure the reliability and durability of power supply network,designers have to assess and analyze the corrosion data and behaviors of transmission tower materials,as an important scientific basis for design and maintenance.However,investigation on corrosion rate assessment and corrosion behavior of transmission tower is still insufficient among China Southern Power Grid region.Therefore,this paper aimed to carry out the evaluation of atmospheric corrosivity category and corrosion behavior analysis among China Southern Power Grid region.Firstly,based on the transmission line network in Guangdong province,10 representative lines?totally 50 exposure sites?were carefully selected which involved the four typical atmospheric environments of the marine,industrial,urban and rural and the exposure tests for one year of Q235 steel on transmission towers in these 50 exposure sites were carried out.Then the corrosion rates were calculated and corrosion categories were evaluated by analyzing the retrieved samples at the time points of 6 and 12 months.Moreover,X-ray diffraction?XRD?and scanning electron microscopy?SEM?were used to analyze the composition and morphology of the corrosion products in the four typical environments.At the same time,Q235,Q345 and galvanized steel were exposed in Huadu atmospheric corrosion station for two years,and then samples were retrived after exposed for 3,6,12 months?two-year samples are not avaible up to now because the deadline is not arrived?,in order to analysis the corrosion resistance and behavior of the three common transmission tower materials.Finally,concerning the short exposure time on sites,indoor salt spraying tests for 2,6,24,48,72,144,240,360 hours of Q235,Q345 and galvanized steel were carried out to accelerate the corrosion,for the purpose of studying the orrosion kinetics and characterizing the corrosion product evolution with exposure time systematically.The field exposure tests of Q235 steel among Guangdong Province showed that,the annual average corrosion rate?rcorr?of the 10 cities varied from 158.47 to 302.37 g/?m²·a?,including 8 cities of C3 level and 2 cities of C2 level.The annual average rcorr of the 50 exposure sites varied from 131.42 to 1017.26 g/?m2·a?,including 1 site of C5 level,1 site of C4 level,34 sites of C3 level and 13 sites of C2 level.Therefore,the main atmospheric corrosion categories were C3 and C2,which indicated medium or low corrosivity among Guangdong Province.By analyzing the mass loss in different typical atmospheric environments,it was found that the rcorr decreased exponentially with the distance to the seaside in the marine climate;The rcorr decreased exponentially or linearly with the distance to the pollution source in the industrial climate;The rcorr only fluctuated in a small range in the surrounding area of the urban climate cities;The law of rcorr in the rural climate was similar to that of the urban clamate,but its value was relatively low.In addition,the morphologies of corrosion products differed with atmosphere: the corrosion products showed sharp structure in the marine climate,flower structure in the urban climate,fine needle structure in the industrial climate and semi-crystalline silk and net structure in the rural climate.In general,the more serious the corrosivity of the sites,the sharper the structure of the corrosion products was formed.The test results at Huadu atmospheric corrosion station showed that,the short-term corrosion kinetics of Q235,Q345 and galvanized steel followed the law of linear function.The rcorr between Q235 and Q345 differed slightly.However,the rcorr of galvanized steel was only 1/24 of the two carbon steels,which performed excellent resistance to atmospheric corrosion.With the increasing of exposure time,the flower structure of g-FeOOH became finer,and the cotton structure of a-FeOOH became sharper and denser,which enhanced the protection of the rust layer on Q235 and Q345.The rust on galvanized steel was smooth and dense all the time.The corrosion kinetics of Q235,Q345 and galvanized Q235 steels from the salt spraying tests were found to be consistent with the bilogarithmic equationn C=K×tⁿ.In general the mass losses were in the order of Q235>Q345 >Galvanized Q235 steels.Compared with the mass loss in Huadu atmospheric corrosion station?the rcorr of galvanized was about 1/24 of that of the carbon steel?,it was seen that the corrosion resistance of galvanized steel was greatly weakened in the high Cl-environment.The morphologies after salt spraying test showed the corrosion products formed on Q235 and Q345 contained akaganetite,lepidocrocite,Fe₃O₄ and goethite.With exposure time extension,the relative amount of g-FeOOH increased first and then declined,the relative amount of b-FeOOH ascended and then gently fluctuated,the relative amount of Fe₃O₄ monotonically increased and a-FeOOH appeared after a certain time and then ever increased due to the transformation of g-FeOOH to a-FeOOH.The corrosion products formed on galvanized steel were mainly simonkolleite,zinc carbonate hydroxide and original zinc oxide all the time.