| Abstract: | Microbial induced corrosion (MIC) in marine environment Steel box‐piles immersed in brackish water of the Baltic Sea show a perforation of the wall (10 mm of thickness) after a service life of 35 years. The calculated corrosion rate by that is 290 μm/a and is much higher than usual corrosion rates in marine environments. Investigations of material have shown, that the steel corresponds well with a common mild steel used for sheet piles. At the outer plain the structure shows normal surface corrosion, while inside, according to microscopic studies, pitting corrosion occurs. Beneath the oxidative corrosion product (e.g. γ‐Fe2O3, maghemite) there are sulfur enriched phases as well as elementary sulfur detectable (by means of different methods like X‐ray Diffraction, REM‐EDX and IR‐Spectroscopy). The corrosion products are covered with a calcitic layer and have to be removed prior to investigation. By means of microbiological techniques, “sulfate reducing bacteria” (SRB) could be detected in high concentrations between the corrosion products inside the steel structures. These bacteria are deriving from the marine sediment and earn their energy using electrons from the steel accompanied by chemical reduction of the sulfate from the sea water. By that the anodic process of iron dissolution is accelerated. The anaerobic environment inside the closed structures promotes the metabolic activity of the bacteria. As a first and cost saving repair it is proposed, to force the oxidation by opening the structures. Of course preventative corrosion protection – coating (inside and outside) or filling (inside) – would have been the best prevention of corrosion. |
