The Effect of Biofilm Formation in Singapore Seawater on Corrosion of Metal and Alloys: New Observations and Concepts

Biofouling and microbiologically influenced corrosion (MIC) can dramatically reduce the function and lifetime of marine structures. These are mediated by micro-organisms attached to the metal surface and/or embedded in a gelatinous organic matrix (the biofilm). The attachment, development and detachment processes of biofilms lead to an important modification of the metal/solution interface, inducing changes in the type and concentrations of ions, pH, oxygen levels, flow velocity and buffering capacity of the liquid microenvironment or the interface. This feature drastically changes the classical concept of electrochemical interface used in corrosion studies. However, the corrosion characteristics, concepts and mechanisms may depend on the specific conditions; e.g. the influence of particular environment, biofilm characteristics, type of alloy etc. Stainless steels top the list of the metal and alloys used in marine applications. Ennoblement of stainless steel due to biofilm formation is one of the major problems in sea water applications related to microbiologically influenced corrosion, which may eventually lead for failures. There was lack of data to validate this phenomenon in Singapore and tropical sea water. Therefore, corrosion behavior of marine grade stainless steels and some designs to replicate oil and gas industry has been studied. In situ electrochemical investigations have been conducted and results have been compared to those obtained from Brest, France. For a biological perspective to support corrosion mechanisms, a microbial analysis of biofilm was also performed and results were correlated with corrosion and electrochemical data. Notable differences were observed in Singapore data in contrast to other reported data, and explanation and possible corrosion concepts will be elucidated. Furthermore, crevice corrosion initiation and propagation mechanisms of duplex stainless steels in Singapore sea water were also investigated