Microbiologically influenced corrosion in maritime vessels

The environmental conditions in many locations on board maritime vessels can favour the proliferation of microorganisms associated with microbiologically influenced corrosion (MIC). This paper will broadly review the internal and external environments for ships and submarines, and provide several case histories of MIC in maritime vessels, both merchant marine and naval. The main focus will be consideration of the various complementary approaches required to unequivocally diagnose the presence of MIC, possibly in the presence of alternative corrosion mechanisms, and then to categorise and quantify the microbiological species present. Particular consideration is given to diagnosis that is applicable to field testing, as well as techniques that are more suitable for confirmatory laboratory based testing. Quick but accurate diagnosis is essential on maritime vessels and in shipyards where maintenance activity must be tightly scheduled and controlled, to control costs and to maximise availability. The paper also considers developments in MIC sensors, for monitoring vulnerable regions of maritime vessels, and providing early warning of the risk or onset of MIC so that preventative maintenance activity can be better scheduled. This is part of an industry move towards Condition Based Maintenance, and is equally applicable to minimising the effects of MIC on shore-based infrastructure. Finally, a brief survey of possible mitigation techniques to reduce the propensity or severity of MIC is discussed. Overall the paper considers the diagnosis, measuring and monitoring of MIC in maritime vessels from a pragmatic, operatorbased viewpoint, allowing future integration with mitigation strategies that are aimed to minimise the impact on through-life costs of maintenance and repair, while maximising operator availability.