Modeling microbiologically influenced corrosion of N-80 carbon steel by fuzzy calculus
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12/29/04
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Modeling Microbiologically Influenced Corrosion of N-80 Carbon Steel by Fuzzy Calculus REZA JAVAHERDASHTI To investigate microbiologically influenced corrosion (MIC) risk using fuzzy logics, weight loss study of N-80 steel was carried out under three circumstances: (1) abiotic, (2) completely biotic (no biocide), and (3) biotic with almost enough biocide (underlined are fuzzy expressions). The microorganism employed was sulphate-reducing bacteria (SRB). Also, effective concentration of a biocide to kill the bacteria was investigated and recorded. Using fuzzy logics and calculus, it was shown that (fuzzy) probability of risk of MIC in the biotic system without biocide was 60 pct, whereas with almost enough biocide, the risk was 50 pct. Different from being absolute risk values, these risk values showed that fuzzy logics methods had the capability of showing how vulnerable a system could be to MIC.
I. INTRODUCTION
MICROBIOLOGICALLY influenced corrosion (MIC) is a kind of electrochemical corrosion in which certain microorganisms either initiate or enhance corrosion.[1] This type of corrosion, which accounts for at least 20 pct of all the damages caused by corrosion,[2] causes an estimated direct annual cost of around US$30 to 50 billion to industry.[3] Of the types of bacteria that do enhance corrosion in almost all engineering materials, one may mention sulfate-reducing bacteria (SRB). This type of bacteria has very corrosive effects on almost all types of engineering materials such as steels and their weldments. The SRB and their importance from the standpoint of MIC have been reviewed elsewhere.[4] To give an idea of how unpredictable the effects of usual corrosion mitigating methods can be on MIC, one may consider application of cathodic protection (CP), which is a way of reducing unwanted effects of corrosion. Although, Pope et al. have shown that,[5] in some cases, CP values up to 1.1 V may not be capable of preventing the growth of bacterial species on metal surfaces and may actually promote the growth of certain microbes, CP is still one of the methods that is used to limit MIC effects.[6] Presenting a model that can describe or predict MIC has always been attractive to researchers: a model based on the assumption that a portion of a pipe can be taken as a chemostat, a thermodynamical model for prediction of MIC by SRB, and also three models for describing and predicting features of MIC.[7,8,9] The author, in one of his previous works,[10] used a fuzzy approach for defining complexity of under-biofilm conditions and involvement of different biological/chemical factors in MIC. Also, in another work,[11] corrosive conditions in a cathodically protected pipe with fuzzy sets concepts were modeled. It seems possible that fuzzy calculus can be used to consider the contribution of factors such as welding to increasing MIC.[12]
REZA JAVAHERDASHTI, Researcher, formerly with the Iranian Corrosion Association, Iranian Corrosion Association, IROST, Tehran, Iran, is with the School of Phy
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