Impact of biological factors on the ennoblement of stainless steel in Baltic seawater

Open circuit potentials of stainless steels increased when immersed in the Baltic Sea. The ennoblement potential was +200 mV(sce) in 40 to 50 days whe n sea water temperature was below 5 degrees 0 and +300-400 mV(sce) within < 40 days at around 10 degrees C, Ennoblement occurred in a laboratory ecosys tem at 23 degrees C in 20 to 30 days, and at 26 degrees C in <20 days, but no ennoblement occurred at greater than or equal to 32 degrees C within 40 days. By the time the ennoblement was complete, compact microcolonies cover ed 1-10% of the steel surface. Nutrient enrichment of Baltic Sea water by t wofold above the natural levels increased microbial growth but attenuated o pen circuit potential increase of the stainless steels. Exposure of the enn obled stainless steels to similar levels of nutrients did not reverse the a lready developed open circuit potentials. Attenuation of the ennobling resp onse of the stainless steels by increases of temperature and eutrophication suggests a role for microorganisms which is crucial for the electrochemica l behaviour of steels in brackish Baltic Sea water.