Pitting corrosion of carbon steel caused by iron bacteria

Corrosion mechanism of 1020 AISI carbon steel was studied in iron bacteria contaminated water. A mixed culture of iron oxidizing bacteria, originally isolated from rust deposits of a clogged carbon steel heat exchanger was used. Weight loss and electrochemical measurements were carried out in 1 g l−1 NaCl solution with or without the addition of iron bacteria culture. The experimental results show that addition of the iron bacteria culture to 1 g l−1 NaCl solution induces a drastic ennoblement of corrosion potential (Ecorr) from −0.75 to −0.25 V (SCE) and surface passivation. Through further exposure, Ecorr slowly shifted back and the steel underwent a severe pitting attack, an effect which was not observed with 1 g l−1 NaCl solution alone or when augmented with a nutrient medium. Electrochemical measurements show that the experimentally observed strong acceleration in pitting corrosion process occurred due to an increase in both cathodic and anodic reaction rates, induced by the iron bacteria.