Influence Of Biofouling On Corrosion Of Carbon Steel In Seawater

Biofouling is the important factor of seawater corrosion of carbon steel and low alloy steel. Recently ,the effect of biofouling to corrosion of steel have drawn many researchers'attention. The macrofoulings and microorganisms on the surface of carbon steel coexist and affect one another, thus they both have effect on corrosion. they must be simultaneously considered while studying the effect of biofouling to seawater corrosion of carbon steel and low alloy steel. Corrosion of carbon steel in the seawater may change with the time,and the effect of fouling organisms may also change.So,the research of corrosion influenced by biofouling should be considered on every stage.With the field exposure method,the appearance and characteristic of carbon steel exposed to the seawater of Qingdao and Xiamen of China from a quarter year to four years was detected,also their relationship was discussed. Moreover,the SRB numbers in the internal rust layer of marine foulings and deposit rust layer were achieved with the MPN method and then the relationship between biofouling and local corrosion of carbon steel.In addition,with the field exposure method, samples are exposed for various time (1~720d), corrosion potential,polarization curve and electrical impedance spectro- scopy are measured, and the electrochemical behavior of carbon steel in seawater was studied, and the corrosion mechanism was analyzed .While , surface topography in different stages was observed using SEM.Moreover,the samples of carbon steel were exposed in natural and sterile seawater for various time(1~90d) in constant temperature 30℃and were taken periodically after different exposure stage . surface topography in different stages was observed using SEM. in different stages., the corrosion mechanism was analysed and it's change using measure of erode electric charge polarization curve and electrical impedance spectroscopy in natural and sterile seawater。The main results and conclusions are summarized as follows:(1) SRB existed in internal layer both under the marine foulings and deposit rust layer.Macrofouling and surface topography of rust layer of carbon steel corresponded well.(2)Corrosion on the surface which was covered with marine foulings with hard shells was slighter than that was covered with with loose salmon pink rust layer because of lower activity of SRB and lower oxygen content.(3)SRB was detected in the internal layer of carbon steel which was exposed to the seawater in Qingdao for 3d.while,corrosion of carbon steel exposed to the seawater was remarkably affected by SRB . In the beginning,corrosion of carbon steel in the seawater was affected by the oxygen contents.With the increase of corrosive microbes(primarily SRB in rust layer), metabolite and reaction product(such as H2S,FeS), when their effect of accelerating corrosion was bigger than restrain corrosion caused by rust layer which hold up oxygen diffusing, and corrosion rate of carbon steel increased.(4) The electrochemical test revealed that mechanism that carbon steel was exposed on two mediums was different. Carbon steel exposed to the natural seawater was affected by the combined action of biofilm and corrosion product film ,while that exposed to the sterile seawater was only affected by the corrosion product film .