THE SINGLE EFFECT OF MICROBE ON THE CORROSION BEHAVIORS OF 25 STEEL IN SEAWATER

Biological elements have a significant impact on lifetime prediction of marine carbon steel facilities. Microbe can produce pitting, crevice corrosion, selective dealloying and stress-oriented hydrogen-induced cracking, which accelerate both localized and average corrosion rates of carbon steel. The formation of microbe films can also reduce the corrosion rate of 25 steel through inhibition of oxygen diffusion and depletion of oxygen in the electrolyte and metal/solution interface. The research on the single effect of microbe on the corrosion behaviors of metal is insufficient up to now. In this work, the single effect of microbe on the corrosion behaviors of 25 steel was studied by comparing the corrosion behaviors of the carbon steel in natural seawater and in sterile seawater. The results show that in most of immerging periods, the bacterial activity at the interface accelerated the average corrosion rate of 25 steel. When the corrosion time was 365 d, the average corrosion rate of 25 steel immersed in natural seawater was 2.6 times that in sterile seawater. However, when the corrosion time was 28 d, the biofilms inhibited the corrosion of 25 steel. The species and contents of microbes significantly influenced the corrosion behavior of 25 steel. The microbes in the corrosion product mainly consisted of pseudomonas, vibrio, crenothrixandleptothrix, thiobacillus and sulfate-reducing bacteria. When the corrosion time was 365 d, flavobacterium also existed in the corrosion product. The contents of aerobe, facultative anaerobe and anaerobe reached the maximum value when the corrosion time was 28, 91 and 184 d, respectively. The regular change of the contents of microbes with the immerging time led to the different microbe corrosion mechanisms of 25 steel.