The Study On The Evolution Of The Initial Stages Of The Rust Layers Formed On The Q235and09CuPCrNi-A By Atmospheric Exposure

The research on long-term exposure of carbon steel is interested in the structure andcomposition of the rust layer covered on the carbon steels. neither the evolution of therust layer, nor the relationship between the evolution of the rust layer and theenvironmental factors has been studied. The effect of environmental factors play acrucial role on the evolution of the rust layer, after the formation of rust layer, theresearch on the long-term rust layer can get longer law of corrosion, how theearlier-stage rust layer effect on the development of later-stage rust layer is stillunknown. Recently, most of the research is interested in the single factor that acceleratesthe corrosion of steels. the influence of various environmental factors on atmosphericcorrosion were no quantitative analysis.Aiming to deal with the problems above, the following schemes have beenperformed: short cycle exposure of steels, to study the evolution of early-stage rust layer;the samples were exchange to exposure between two different site, to study the effect ofearlier-stage rust layer on the development of later-stage rust layer; exposuring thesamples at different time node, to study the effect of various environment factors on thedevelopment of corrosion.The results were shown as follows:(1)Corrosion behavior in the early stage of carbon steel Q235and weathering steel09CuPCrNi-A exposured in WuHan station and petrochemical station were studied.Weathering steel exposured in petrochemical station embodied weatherability faster thanthe exposure in WuHan station. The weighet loss of weathering steel is higher than Q235in the early-stage exposure. Exposuring the samples in the petrochemical environmentwill promote the formation of α-FeOOH. The redox reaction of the rust layer worked inthe early stage can be divided into two stages:The first stage,the redox of the rust layerproduct fasterly,while the second stage, with the accumulation of Fe3O4theelectrochemical activity of the rust layer was increased.(2)The samples exchanging in three different station environment were studied byweight loss. The samples which has been exposured in WanNing got a high weight loss.Exposuring the samples in WanNing for nine months after the samples exposured inother two site for three months,found that the early-stage samples layer with protective rust layer will accelerate the corrosion of the samples. The results shows that the rustlayer of the sample exposured in WanNing station have significant influence on thedevelopment of the later-stage rust layer.Two simulated solution, NaHSO3and NaCl, was implied in accelerating the corr-osion of Q235which was accelerated in one them for30CT, and to-ok out accelerating in the other solution for30CT. Its protection of earler rust to the wei-ght loss of the development of later corrosion. But the result of experiment is same asthe results exchanging in WanNing station and other stations,XinJiang and Wuhan, sho-wing that the early-stagerust layer formed in the envirenment contains Cl-has effect o-n corrosion of the later-stage rust layer.(3)Conbined the samples which exposured in different seasons with seasonalfactors, found that humidity and precipitation are the main factors which have effects onthe corrosion of Q235. The pollution level of Xinjiang station is relatively small, thecorrelation coeffient between weight loss and precipitation reached the maximum1. Thecoeffient in petrochemical station only reached0.8with the effect of sulfur contaminantsin atmospheric. Indicating that weight loss of the samples may be affected by th-ese pollution factors. Analyzing the correlation coefficient calculated betweenthe environment factors and the weight loss of WuHan station exposure in differentseasons,found that the weight loss of the samples exposure in WuHan is affected mainlyby the combination effects of these facts.By analyzing two different carbon steels, Q235and09CuPCrNiA, exposured in twodifferent environment contaminated for7days, the ariticle did the monitoring ofpollution factors in real time, and drew a conclusion that the precipitation is the maininfluence factor. It is calculated that the H2S, sulphation rate and sea salts havesignificant influence on the two steels mentioned above.