Corrosion of X65 steel by Pseudomonas sp. in planktonic and sessile states and inhibition effect of cathodic polarization

In harsh marine environment, corrosion is a serious problem, among which microbiologically influenced corrosion is particularly common and complex. This work studied corrosion of X65 steel by planktonic and sessile iron oxidizing bacteria (IOB), i.e. Pseudomonas sp. isolated from coastal water of Qingdao, and inhibition effect of cathodic polarization. Results demonstrate that both the planktonic and sessile IOB caused the corrosion of X65 steel by promoting the oxidation of ferrous ions, but the contribution of sessile cells was far greater than that of planktonic cells. Cathodic polarization kills sessile cells on the metal surface and prevent attachment of IOB. With a negative shift of the cathodic potential, the inhibition effect was enhanced. Cathodic polarization altered interface properties of X65 steel, affecting adhesion and corrosion process of IOB cells. However, when X65 steel was sufficiently polarized to −1050 mV vs. SCE, IOB produced more extracellular polymeric substances to resist stimulation by an external electric field. Therefore, cathodic polarization could not completely remove sessile IOB cells, and pitting corrosion existed on the metal surface.