| With the rapid development of economy, water bodies especially the urban lakes are polluted by nitrogen and phosphorus in various degrees seriously in our country. At present, the eutrophication of water bodies has become a typical and widespread phenomenon. Fresh water is also an important place where the metal materials are being serviced. Water eutrophication will lead to the changes of the service environment, therefore corrosion behavior and laws of metal materials will be changed. From now on, studies on metal corrosion in water pollution mainly concentrated in pipeline corrosion impacted by the pollution of water bodies, and corrosion laws and mechanism of alloy in pollution seawater, etc. But the study on metal corrosion behavior impacted by eutrophic water is less reported. In this paper, supported by National Natural Science Fund, A3 steel which is common used at hydraulic structures is taken as the research object, and East Lake eutrophic water is chosen as the water body, The corrosion behavior of carbon steel impacted by eutrophic water are studied. The main works and study results are as follows:(1) The study of influence on indicators of water quality by water eutrophication. Compared with the measurement results of water quality in one year between the clean water (Danjiangkou Reservoir) and the eutrophic water (Shuiguo Lake of East Lake), the changes of water quality indicators mainly has been found that the reducing of dissolved oxygen, the increasing of the concentration of total nitrogen and total phosphorus, the enhancing of the content of suspended solids and micro-organisms and the growing of the number of toxic and harmful substances in water after eutrophication.(2) By field tests and water body simulation tests in laboratory, corrosion type, rate, products and morphology of carbon steel in eutrophic freshwater (East Lake water) and cleaning water (Danjiangkou Reservoir)are researched, and further results confirm the law that carbon steel corrosion rate in pollution water (eutrophic water) is slower than that in clean water; the study on carbon steel corrosion impacted by different hanging depth of sample shows that A3 steel corrosion rate increases with the depth of hanging. This phenomenon is due to the difference of biomass caused by different illumination at different hanging depth. This law is first reported by my group, it is significant to understand the impact of microorganism to metal corrosion in freshwater environment; the study of metal corrosion impacted by the season of hanging sample shows that seasonal impact, the corrosion rate of A3 steel hanged at summer (2007,07-2008,07) is faster than the that hanged at winter (2005,12-2006,12).(3) The study on corrosion mechanism of carbon steel caused by main water pollutants in eutrophic water. The influence of water pollution indicators for the carbon metal corrosion has been researched in the eutrophic freshwater which has total nitrogen (ammonium, nitrate, nitrite, organic nitrogen substance), total phosphorus (phosphate, hydrogen phosphate, dihydric phosphate, organophosphorus material), chemical oxygen demand (COD), suspended solids (kaolin), organic pollutants (organophosphorus pesticide, organonitrogen pesticide). The results show that:in case of that the rate of water flow can be neglected, A3 steel corrosion rate increases with the concentration of dissolved oxygen, decreases with the COD value, when COD> 120mg/L, the change of A3 steel corrosion rate is slow, lower linear with pH value increasing, decreases with the concentration of total nitrogen (TN) in water. Ammonium in fresh water is an inducement of corrosion of A3 steel, mainly impacting oxygenation reaction of A3 steel cathode process. Nitrite and nitrate mainly inhibits A3 steel anodic process, which reduces the corrosion of A3 steel; A3 steel corrosion rate decreases with total phosphorus (TP) concentration in water. phosphate, hydrogen phosphate, dihydric phosphate and polyphosphate reduce the corrosion of A3 steel, because deposition film is formed on the surface of A3 steel, which restrains A3 steel anodic process; A3 steel corrosion rate decreases with kaolinite content; organophosphorus pesticide (diethyl phosphite) in water can promote A3 steel anodic process to accelerate the corrosion of carbon steel; organonitrogen pesticide (urethane) inhibits A3 steel anodic reaction, reducing the corrosion of A3 steel.(4) The study on corrosion of carbon steel impacted by bacteria in eutrophication water. By cultivating, separating and purifying bacteria in corrosion product film on the surface of sample hanged in East Lake, and 7 kinds of dominant bacteria are screened out and identified. The bacteria are mainly belonging to the species of Comamonas and Pseudomonas, and small amounts are belonging to the species of Myroides. Nitrogen, phosphorus and small molecule can promote the growth of bacteria, and the initial stages of corrosion, the surface of A3 steel covered by microbe (bacteria and algae) in freshwater can slow down the corrosion rate, they participate in forming the corrosion product, and make the product film compact and component complex.(5) Discussing the corrosion mechanism of A3 steel in eutrophic water using electrochemical methods; putting forward an function mechanism model of main environmental factors in eutrophic water to carbon steel corrosion; Multiple Grey Predicting Model MGM(1,3) is established to predict A3 steel corrosion behavior in the clean freshwaters and eutrophic freshwaters respectively, and the accuracy of MGM(1, 3) is one grade. |
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