New Research Findings for the Atmospheric Corrosion of Steel Structures and the Development of Predictive Models for Corrosion Loss

Atmospheric corrosion of structural steels in the coastal zone is of significant economic performance, impacting on off-shore, port and harbour and industrial structures as well as ships, tanks and pipelines. However, despite much understanding of the fundamentals of the corrosion process, the tools available to structural engineers for predicting the initiation and the progression of corrosion are not sophisticated. This paper will outline the current situation and describe current efforts to develop predictive models for corrosion loss and for maximum pit depth for steels exposed to tidal, splash and coastal zone exposures. The models are based on the analysis of world-wide data and on corrosion science fundamentals. They also include recently developed understanding and research findings that demonstrate the critical role of bacteria in the overall corrosion process. The involvement of bacteria both in very short-term corrosion and in long-term corrosion has been demonstrated through detailed investigations of steels exposed in natural environments rather than in the laboratory. Bacterial culturing techniques, widely used in the offshore oil industry for example, are known not to be very reliable and for this reason the research has turned to the use DNA analysis to confirm the presence and numbers of bacteria involved and to allow their identification. The paper will give examples of the surfaces of steel exposed to sterile and to natural sea waters to demonstrate the importance of bacterial activity. This has important implications for the prediction of likely corrosion in polluted atmospheres and marine exposure conditions.