Combined Influence of Microorganisms and Direct Current on the Corrosion Behavior of X70 Steel in Near‐Neutral Solution

ABSTRACT Stray currents significantly affect microbial metabolism and pipeline corrosion. This study explored the corrosion of X70 steel in near‐neutral solution under direct current (DC) and sulfate‐reducing bacteria (SRB). The corrosion rate was determined with the electrochemical technique and the corrosion morphology and corrosion products were respectively characterized by SEM and XPS. Results showed minimal uniform corrosion was observed in sterile solution without DC, but pitting corrosion occurred in bacterial solution. Without SRB, DC caused extensive corrosion, and the corrosion rate first dropped, then rose with increasing DC density, hitting a minimum at 0.5 mA/cm 2 . When DC and SRB acted together, the corrosion rate was higher than with DC alone, followed a similar trend, and correlated with SRB activity. At 0.1–0.5 mA/cm 2 DC, SRB activity increased and dominated corrosion, causing pitting. However, at 1 mA/cm 2 DC, SRB was suppressed and DC took over, and severe pitting was observed. In sterile solution, DC facilitated the formation of protective Fe 2 O 3 and Fe 3 O 4 layers. Conversely, in bacterial solutions, the corrosion product FeS inhibited the oxidation of Fe 2+ by DC.