The Corrosion of Structural Steel in Seawater

This paper provides an overview of recent research into the modelling of the loss of material for structural steels continuously immersed in seawater. Until recently the available engineering literature in this area has been able to provide only very general information, perhaps sufficient for conservative approximations suitable for the design of new structures. However, it is insufficient to predict the likely loss of steel with time. It is even less suitable to predict the additional losses that may occur for already partly corroded structures. Field trials to assess the likely 'engineering' corrosion rates are expensive, take a long time and may be misleading. An alternative approach is to use the basics of corrosion mechanics to developed engineering models for prediction of corrosion. A recently developed multi-phase model for corrosion loss with time of exposure is presented. This model, already accepted in the corrosion literature, indicates that metal oxidation as conventionally associated with corrosion is only one part of the overall process. In the longer term corrosion induced by anaerobic bacteria is the governing mechanism. This has major practical implications for the assessment of infrastructure. Various research findings for the effect of water temperature, dissolved oxygen levels, nutrient pollution, depth, water velocity and water salinity are reviewed.