| In the cooling water system, the heat exchanger is an equipment that transfers heat fromhot fluid to the cold fluid, it has been widely used in many industrial fields such as chemicalindustries, oil refining, power industries, etc. Among many factors, microorganisms, scale andcorrosion are the three most important adverse effects on cooling water heat exchanger workand life, it will cause the perforation and brittle fracture of device pipeline. In this paper,according to the characteristic of duplex stainless steel corrosion resistance and the importanceof the cooling water heat exchanger, the duplex stainless steel is selected as the material ofheat exchanger, the electrochemical test, SEM, EDS analysis, and weight loss were used tostudy the corrosion behavior and mechanism of the duplex stainless steel in cooling watersystem of different Cl-content, different microorganisms and under the combined action ofcorrosion anion and microorganism. There search results will provide theoretical basis for theapplication field of Duplex stainless steel and previous research results of laboratory in thepetrochemical enterprises. The research results showed that:(1)2507duplex stainless happened slight corrosion, and have shown a good passivationproperties and corrosion resistance in cooling water system under the action of thedifferent content of Cl-, different microorganisms, and the combined action of corrosionanion and microorganism.(2) The SEM and EDS analysis results showed that:2507duplex stainless steel wereimmersed in cooling water simulated solution which contained in different content of Cl-atdifferent days, Cl-destroyed the passive film of2507duplex stainless steel surface, it isthe main cause of pitting which2507duplex stainless steel happened, and corrosionproducts are mainly iron oxide and sulfide;2507duplex stainless steel were immersed incontaining IOB cooling water simulated solution at different days and in different contentof IOB cooling water simulated solution, IOB were adsorbed on the steel surface, thebiofilm and metabolites generated by IOB would form the nodulation on the surface ofsteel, so the areas between bottom and periphery of nodulation can be formed an oxygenconcentration cell, which will promote the occurrence of pitting, and microbial membraneare mainly iron oxides;2507duplex stainless steel were immersed in containing SRB cooling water simulated solution at different days and in different content of SRB coolingwater simulated solution, SRB were adsorbed on the steel surface, the main metabolitesS2-can generated by SRB growth activity, S2-could happen reacts with Fe2+to formhighly insoluble FeS precipitation which can accelerate the anode reaction, thus thedamage degree of corrosion of passivation coating on the steel surface will increase, theresistance to corrosion will decrease, sensitivity of corrosion will increase, and microbialmembrane are mainly iron sulfide;2507duplex stainless steel were immersed incontaining SRB+IOB cooling water simulated solution at different days, under thesynergistic action of adsorbed SRB and IOB on the steel surface, their metabolites and Cl-,the corrosion damage of passive film for2507duplex stainless steel surface will increase,the corrosion products are mainly sulfide and oxide of iron.(3) Electrochemical analysis results showed that: with the increase of immersed time, the rateof corrosion and corrosion tendencies of2507duplex stainless steel are first increase andthen decrease in cooling water simulated solution; with the increase of Cl-content, thecorrosion tendencies for2507duplex stainless steel were immersed in cooling watersimulated solution after60days is first decrease, then increase, and decrease again, the rateof corrosion is first increase and then decrease; with the increase of immersed time, thecorrosion tendencies for2507duplex stainless steel were immersed in containing IOBcooling water simulated solution is first decrease, then increase, and decrease again, therate of corrosion is first decrease, then increase, and decrease again, and increase at last;with the increase of IOB content, the corrosion tendencies for2507duplex stainless steelimmersed in cooling water simulated solution after30days, the rate of corrosion andcorrosion tendencies are first increase and then decrease; with the increase of immersedtime, the corrosion tendencies and rate of corrosion for2507duplex stainless steelimmersed in containing SRB cooling water simulated solution are first increase, thendecrease, and increase again, and decrease at last; with the increase of SRB content, thecorrosion tendencies for2507duplex stainless steel were immersed in cooling watersimulated solution after30d, the rate of corrosion and corrosion tendencies are firstdecrease and then increase; with the increase of immersed time, the corrosion tendenciesfor2507duplex stainless steel were immersed in containing IOB+SRB cooling watersimulated solution is first increase gradually and then decrease, the rate of corrosion isfirst decrease and then increase, and decrease again, and increase at last;(4)2507duplex stainless steel were immersed in these four different simulated solutioncontaining Cl-, IOB, SRB and SRB+IOB cooling water after10d,the order of corrosiontendency is IOB <SRB+IOB<Cl-<SRB; the order of corrosion rate is IOB <Cl-< SRB+IOB <SRB... |
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