The critical involvement of anaerobic bacterial activity in modelling the corrosion behaviour of mild steel in marine environments

Abstract

The modelling of both short- and long-term corrosion loss and maximum pit depth is increasingly of interest to engineers and others interested in predicting the remaining life of coastal and ocean infrastructure. Traditional models are demonstrably of poor quality. A more refined modelling approach applicable both to corrosion loss and to pitting of mild steel in marine environments is described. A crucial aspect is that explicit consideration is given to the influence of microbial activity. The model is unique in that it considers the governing corrosion process to change with increased exposure time. The rationale for this approach and some of the key findings are described. It is supported by observations of the corrosion response to changes in metal alloying and to water pollution effects. The model also permits more rational explanations to be offered for the effects of water velocity, depth of immersion and seawater salinity. Recently the effect of anaerobic bacteria on very early corrosion has been re-examined and an explanation offered in terms of the influence of water pollution on the initial corrosion rate. Applications to pitting corrosion of mild steel has led to new interpretations of pit data and new interpretations for the probability distributions associated with maximum probable pit depth. The model has been calibrated using an extensive re-examination of literature data and extensive use of specially commissioned field tests.