Assessment and Control of Microbial Induced Corrosion in Sae Water in Nuclear Power Plant Materials

Abstract

Microbial-induced corrosion (MIC) can occur due to the long building timeframes connected with nuclear facilities and the huge number of redundant or standby systems where water is permitted to remain stagnant for long periods of time. MIC affects carbine and low-alloy steels, stainless steels and copper alloys are all susceptible to MIC in raw water applications. Visual examination is especially helpful in performing preliminary assessments of MIC. If properly diagnosed, MIC can be effectively treated during plant development, operation and brief shutdowns. The main aim of this work is directed to investigate some methods for evaluating and controlling one of the most important economic problems arose from the presence of some microorganisms which are responsible for promoting corrosion process of metals and/or their mixtures (alloys) in cooling water systems and those in different Egyptian industrial fields such as power stations, oil fields and power plants. The study concentrated on finding applicable treatment methods for controlling Thiobacillus bacteria which represent one of the important active members of microbiologically induced corrosion (MIC) group found in seawater, through recording their growth and reducing their activities, and consequently reducing the harmful impact of its presence in different industries as mentioned above.The current research is also concerned with the scales formation studies for water and the effect of scales inhibitors on the scales formed during cooling processes. Moreover, this research includes and discusses the results of using some special biocides as a chemical method applied for reducing microbial counts and its efficiencies on Thiobacillus bacteria. Benzalkonium bromide, Sodium hypochlorite and Gluteraldehyde were chosen for the present study because of their broad spectrum and biodegradability. A strategy is developed for inhibiting Thiobacillus bacterial colonization and aerobic corrosion in biofilms on mild steel. The most effective biocide was gluteraldehyde that has been used as a reference biocide, its addition firstly prior to Thiobacillus bacterial colonization considered a valuable approach to reduce Thiobacillus bacterial induced corrosion. Gluteraldehyde form biocide which has wide a range of biocidal effects and also inhibiting Thiobacillus bacteria as shown in this study. The results indicated that 50 (mg/L) of Glutaraldehyde was sufficient to eliminate all bacterial counts, but 2.5 (mg/L) of Benzalkonium bromide and 8 (mg/L) of sodium hypochlorite were also required to achieve the same result. The results also demonstrated that high biocide concentration inhibit Thiobacillus bacteria growth more than the low biocide concentration. Finally, the findings support the construction of nuclear power plants in order to prevent aerobic bacteria from causing bio corrosion and to provide media for the growth of anaerobic bacteria such as sulphate reducing bacteria which were previously thought to be the most important bacterial group involved in bio corrosion.