Microbiologically Influenced Pitting Corrosion of Stainless Steel Type 316 in a Seawater Flow Through System

A dynamic study was carried out using a fabricated stainless steel (SS-316) flow-through system. Biofilm (slime) formation and metallic corrosion are conventionally evaluated as separate, independent processes, however, in the present study both were monitored simultaneously. Relevant biofilm parameters were analysed and different types of bacterial population were assayed. In addition, scanning electron microscopy (SEM), EDAX and XRD techniques were used in the evaluation of the corroded specimen. After 165 days of operation, the SS-316 pipe developed leaks due to pipe punctures. Microbiological investigations substantiated the presence of iron bacteria, sulphate reducing and heterotrophic bacteria. Bacterial growth and biofilm formation at 45°C were negligible. SEM images showed many minor pits on the surface along with encrusted filamentous bacteria. Chemical analysis by XRD showed the presence of calcium, sulphur, silica, along with iron sulphide, iron carbonate and calcium carbonate. Based on the putative presence of corrosion causing bacteria and the detection of biologically mediated corrosion products by XRD analysis, it was concluded that the SS-316 tube failed due to microbiologically influenced corrosion (MIC).