August 19, 2019
Author: E. S. Beardwood. NACE Corrosion 1995, Paper No. 201, NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas, 77084, USA. www.nace.org.
ABSTRACT: The detection and control of planktonic microorganisms has been well understood and practiced over the years. However, the fouling and corrosion associated with sessile bacterial development of biofilms continues to be an area of concern. The norm in the industry has been to investigate biofilms associated with corrosion and metal failure long after a reduction in heat transfer efficiency has been incurred. With each case comes additional knowledge and improved understanding of the various processes operating concurrently. Whether corrosion is being directly affected by the presence of microorganisms through hydrogen uptake, production of corrosive metabolites, indirectly through oxygen diffusion reduction or ion transport and concentration, corrosion and enhanced fouling occur. Biofilm growth results in the development of a microbiological community or consortium which, for the most part, can be considered symbiotic. The population distribution will vary from the top layer of aerobes to facultative anaerobes to strict anaerobes at the base metal interface. Throughout each layer there will be distinct species present either in separate blocks or as a mixture. These distinct blocks interact with the inorganics, organics and gases naturally present in the aqueous phase as well as the metabolically converted by-products. A crude biofilm model was hypothesized in 1987 by the author. Subsequent work has been done to date to rationalize the model for user friendly predictive modelling. This paper will discuss the findings and development of said model.