Influence of acidogenic Citrobacter farmeri on the corrosive behaviors of X70 pipeline steel in simulated seawater medium

Abstract

This paper studies the corrosion behavior of X70 steel in a simulated seawater environment with the presence of acid-producing bacteria through the analysis of open circuit potentials, linear polarization resistances, electrochemical impedance spectra, biofilm, and pitting morphology. The C. farmeri bacteria attach to the surface of pipeline steel to form a biofilm, which accelerates the corrosion of the steel. In the C. farmeri medium, the corrosion current (i_corr) (5.77 × 10^–6 A cm⁻²) of the steel specimen is approximately 2.2 times higher than that in the sterile solution. The charge transfer resistance (R_ct) of X70 steel in C. farmeri solution remains significantly lower, while corrosion pits are numerous. These pits are concentrated at microbial enrichment sites and coalesce to form larger ones. The oxygen differential concentration cell, caused by the microbial film layer of transparent mucosa, as well as complexation reactions and citric acid produced by C. farmeri, all contribute to accelerating the local corrosion of X70 steel, thereby resulting in a relatively high corrosion rate.

Graphical abstract