Effects of dissolved oxygen accelerated P. aeruginosa on the corrosion mechanism of X70 steel in simulated marine environments

Abstract

Dissolved oxygen exerts a complex influence on microbial corrosion in marine environments. This paper investigates the effects of dissolved oxygen on the corrosion behavior of X70 steel in seawater, both in the presence and absence of P. aeruginosa, through electrochemical testing, surface morphology observation, corrosion weight loss analysis, and elemental analysis of corrosion products. The findings reveal that the uniform corrosion rate in the anaerobic P. aeruginosa seawater environment was lower than that in sterile seawater; however, localized corrosion was markedly severe, with pitting pits reaching a maximum width of 578.38 μm and a maximum depth of 49.938 μm—significantly greater than the maximum depth of 29.606 μm observed under sterile conditions. P. aeruginosa formed a biofilm on the steel substrate, which promoted localized corrosion. The introduction of dissolved oxygen accelerated the overall corrosion of X70 steel in the presence of marine P. aeruginosa, yielding a maximum corrosion rate of 45.62 mpy after 7 days of immersion, approximately two orders of magnitude greater than the corrosion rate under anaerobic conditions. The presence of dissolved oxygen enhanced the metabolic activity of P. aeruginosa, facilitated redox reactions in the steel matrix, and resulted in the formation of extensive metal oxide and microbial films. These metal oxides, primarily consisting of Fe₃O₄, FeOOH, and Fe₂O₃, combined with microbial cinema to create a composite product layer, significantly impacting the overall corrosion of X70 steel and promoting localized corrosion to a considerable extent.