Mechanism of sulfate-reducing bacteria on the galvanic corrosion of 825/P110 couple

Sulfate-reducing bacteria (SRB), as typical corrosive microorganisms, sustain their metabolic activities by utilizing electrons released during metal dissolution, thereby accelerating metal corrosion. However, their influence on galvanic corrosion between dissimilar metals has been less studied. This work investigates the attachment behavior of SRB on the surfaces of an 825 nickel-based alloy/P110 carbon steel galvanic couple and the underlying mechanism of SRB on galvanic corrosion. The results show that in the SRB-containing system, the galvanic current density of the 825/P110 couple is significantly higher than that in the sterile system, reaching a maximum of 15.82 μA/cm² within 14 days. After coupling, the polarization resistance of P110 steel continuously decreases, indicating accelerated corrosion kinetics, with a more negative corrosion potential and a higher corrosion current density compared with those in the sterile system. Meanwhile, in the SRB-containing solution, the 825 alloy undergoes corrosion, and the weight loss rate of the coupled sample is 2.3 times that of the uncoupled one. Owing to a higher number of attached bacterial cells and the degraded quality of the passive film, the pitting depth on the 825 alloy reaches 15.5 μm, much greater than that on the uncoupled alloy. More corrosion products are observed on the surfaces of both coupled P110 steel and 825 alloy, and pitting pits become visible after product removal. In summary, SRB significantly enhances the galvanic corrosion effect of the 825/P110 couple.