Microbial corrosion of X52 pipeline steel under soil with varied thicknesses soaked with a simulated soil solution containing sulfate-reducing bacteria and the associated galvanic coupling effect

In this work, corrosion of an X52 pipeline steel under soil layers with varied thicknesses soaked with a simulated soil solution was investigated in the absence and presence of sulfate-reducing bacteria (SRB) by weight-loss testing, bio-testing, electrochemical measurements and surface analysis techniques. Results demonstrate that, in anaerobic, sterile soil solutions, the presence of a soil layer on the steel surface accelerates the steel corrosion, with the corrosion rate increasing from 0.01 mm/y for uncovered steel to an average of 0.04 mm/y when the soil layer thickness exceeds 5 mm. The presence of SRB in the soil solution increases remarkably the corrosion of bare steel, with an average corrosion rate up to 0.68 mm/y. However, the presence of a layer of soil on the steel surface decreases the steel corrosion. As the soil layer thickness increases, the corrosion rate further decreases, along with the decreased counts of sessile SRB cells on the steel surface. This is attributed to the blocking effect of the soil layer on transport of SRB cells and nutrients towards the steel surface. A galvanic coupling effect exists between bare steel and the soil-covered steel, where SRB contribute to the galvanic corrosion effect. The galvanic current measured in the presence of SRB is considerably higher than that in the absence of SRB.