Environmental Engineering Reference
In-Depth Information
Figure 3.14
Filiform corrosion under clear varnish on steel (10
).
concentrated solution of ferrous salts and hydrolysis creates an acidic environ-
ment (i.e., pH 1-4). Oxygen that diffuses through the film tends to accumulate
more at the periphery of the solution, i.e., at the interface between the head and
the tail. Lateral diffusion of oxygen serves to keep the main portion of the filament
cathodic to the head.
Filiform corrosion can be prevented by reducing the relative humidity of the
environment to below 65%. Protection can also be achieved by the use of films
of very low water permeability.
Figure 3.15
Schematic cross-section of filiform corrosion illustrating the growth
mechanism.
