Corrosion mechanism of nitrate reducing bacteria on X80 steel correlated to its intermediate metabolite nitrite

[Display omitted] •The uniform and pitting corrosion of X80 steel were accelerated by NRB.•Nitrite, an intermediate metabolite by NRB, can easily induce corrosion.•The corrosion is closely related to the concentration difference of nitrite. The effect of nitrate reducing bacteria (NRB) on corrosion of X80 steel in near-neutral pH solution was studied using various electrochemical and surface techniques. NRB promoted the uniform and pitting corrosion of X80 steel, especially the depth and density of pits. The biofilm formed by NRB hinders the anodic reaction, but still accelerates the corrosion rate. The corrosion of NRB on X80 steel is not only related to the extracellular electron transfer, but also the concentration difference of the intermediate metabolite nitrite. When the nitrite concentration difference is lower than 6 mmol/L, the extracellular electron transfer of bacteria plays a dominant role in differential concentration corrosion, while when the nitrite concentration difference is higher than 6 mmol/L, it is the corrosion inhibition effect of γ-Fe2O3 oxidized by nitrite.