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IRB are a type of microorganism capable of reducing Fe(III) to Fe(II). In terms of their oxygen requirements, IRB include strict anaerobes and facultative anaerobes; in systems where oxygen is introduced frequently, facultative anaerobes have an advantage over strict anaerobes. The effect of IRB on corrosion can be either promoting or inhibitory, and this is closely related to factors such as the strain and the properties of the testing system. Figure 1 shows a schematic illustration of the effect of facultative anaerobic IRB on the corrosion process. In the early stages of corrosion, the dissolved oxygen concentration in the solution is high; the uneven adhesion of IRB on the metal surface leads to a decrease in the local dissolved oxygen concentration. This concentration gradient results in the formation of local anodes and cathodes, thereby accelerating corrosion (A). As the growth of free and attached IRBs consumes oxygen, the concentration gradient of dissolved oxygen on the metal surface disappears, and as a result the local anode and cathode cease to exist ； Once the oxygen on the metal surface is depleted, the facultatively anaerobic IRB switches to using Fe(III) as an electron acceptor, and the resulting Fe(II) diffuses into the bulk solution ； Fe(II) readily reacts with dissolved oxygen, further reducing the dissolved oxygen concentration and suppressing corrosion (B). The corrosion-inhibiting effect of IRB is more pronounced in static systems, as Fe(II) can accumulate in large quantities, making it difficult for dissolved oxygen to reach the metal surface (C). In the flowing system, on the one hand, the generated Fe(II) is continuously carried away, resulting in a low concentration of it ； On the other hand, as oxygen is continuously supplied, local anodes and cathodes reappear, promoting corrosion (D). In addition to the corrosion promotion caused by oxygen concentration cells, IRB’s effect on promoting corrosion can also be achieved by destroying the protective Fe(III) oxide layer on the metal surface. Figure 1 Effect of compatible anaerobic IRB on the corrosion process