Corrosion inhibitors inside the biofilms.

Being a biofilm a differential aeration cell, it deactivates the strong (anodic) corrosion inhibitors, and makes its application disastrous.

As long as the anodic inhibitor is acting at the anodes, the presence of differential aeration cells creates big problems to the system. A differential aeration cell being protected from inhibitors access due to the porous deposit over it, cannot be reached by the inhibitor.

The chromates used as corrosion inhibitors in the past, due to its oxidizing and toxic nature were less suffering from biofilms protections.

Unfortunately, now its use is prohibited due to environmental restrictions, and modern, environmentally friendly, anodic inhibitors (and especially the all-organic or the phosphate/polyphosphate/organophosphate types) are very tasty nutrients for the bacteria into the biofilms.

So the differential aeration corrosion cells remain not only untouched, but they are combined to the entire cathodes of the system collecting the sum of the corrosion potential. The activity of the differential aeration cells and the pitting tendency is highly accelerated, controlled only from the diffusion of the corrosion products through the porous deposit.