Research On Measurement Method Of Mocrobiologically Influenced Corrosion In Cooling Water

Industrial cooling water is a particular environment which is suitable for microorganisms'growing. Sulfate-reducing bacteria (SRB) are the main harmful bacteria in circulating cooling water. Under anaerobic conditions, SRB reproduce a lot to produce mucus, which speed up the formation of fouling, erode the metal equipment, plug the pipeline, affect the efficiency of heat transfer, and bring a lot of inconvenience to the production.304 stainless steel was tested under the media without Sulfate-reducing bacteria (SRB) and with SRB. The corrosion behaviors of 304 stainless steel in SRB and blank culture medium were studied by measuring the open circuit potential, the polarization curves and electrochemical impedance Spectrum, weight loss measurements to get the changes of fore-and-aft corrosion fouling. The open circuit potential shifted negatively with the time. The result showed that the slope of cathodic polarization curves measured in the medium included with SRB is lower than the one obtained in the medium without bacteria, while the slope of anodic polarization curves is higher. It is concluded that the process of anode polarization was repressed at the presence of SRB. With the growth of the culture time , the value of electrochemical impedance in the medium without bacteria decreased at first, then rose, while in the medium included with bacteria fell at all times. It indicated that SRB accelerated the corrosion of stainless steel. With the dipping time, a biofilm, under which corrosion products congregate to form local battery corrosion, was formed on the surface of stainless steel, so that the serious pitting corrosion is induced.The corrosion behaviors of 304 stainless steel in SRB and blank culture medium were studied by electrochemical noise technique. Polynomial fitting was applied to remove the DC trend or drift from the electrochemical noise (EN) data of the corrosion. The data after drift removing was analyzed in time and frequency domain to estimate the type of the corrosion. In the electrochemical noise measurements, there is always noise more or less. If they are analyzed directly, the useful information and data can not be got from them, so they must be de-noised. The principle on the electrochemical noise detected by using wavelet transform was described briefly. The electrochemical noise of 304 stainless steel corrosion which is measured in the solution of sulfate-reducing bacteria were de-noised by using a wavelet threshold de-noising method , which made the quadratic biorthogonal spline wavelet as the mother wavelet and adopted an soft threshold processing function. The results showed that the quadratic biorthogonal spline wavelet much smoother and it can remove the noise from the electrochemical noise effectively, and can effectively identify the location of the sudden changes in the signal and accurately reflect the useful information of the signal.