Microbiologically Influenced Corrosion of High-Resistance Alloys in Seawater

Microbiologically influenced corrosion (MIC) of construction alloys used for subsea applications was evaluated. Susceptibility to MIC of UNS S31603, UNS S31803, UNS S32750, UNS 31254, UNS N06625 and UNS N08825 was assessed by measuring the open circuit potential, cyclic polarization tests, surface analysis and biofilm composition. Samples were tested as-received as well as during and after sample exposure to aerated natural seawater at 30°C for up to four weeks where natural marine biofilms were allowed to develop. Test controls consisted of experiments using filter-sterilized seawater. In order to identify the relationship between electrochemical activity and biofilm composition, DGGE (Denaturing Gradient Gel Electrophoresis) and sequencing were conducted to examine the diversity of the microbial consortia in the marine biofilms covering the materials surface. Results are presented to show the effect of immersion time and the presence of marine biofilms on the electrochemical behavior of the corrosion resistant alloys and hence the resistance to localized corrosion. These results also showed the degree to which material composition may affect the bacterial community and shift the microbial diversity in biofilms.

Keywords: microbiologically influenced corrosion, stainless steels, seawater, biofilms, DGGE, microbial community structure.