3.2. Corrosion potential versus chloride ion content
Fig. 4 shows the relationship between the corrosion potential
and the chloride ion concentration in soils with and without
SRB inoculation. In the two cases the corrosion potential of the
stainless steel decreased with increasing chloride ion concentration.
Furthermore, the corrosion potential in soils with SRB
was more negative than that without SRB, which indicates that
the presence of SRB increases the corrosive tendency of the
steel.
3.3. Influence of SRB and chloride on corrosion of stainless steel
Figs. 5 and 6 show the variation of the average corrosion rate and
the maximum pit depth with the concentration of chloride ions in
soils. The mean of the average corrosion rate was very low, and
there was a peak in each plot. The corrosion rate was faster in the
presence of SRB under the lower chloride ion concentration of 1.0%,
and the corrosion rates of the steel in soils with and without SRB
were almost the same when the chloride concentration exceeded
2.0%. The peak appeared in the middle range because lower or
higher chloride ion concentration could decrease the activity of SRB
[24,25]. Hydrogenase of SRB consumed the H atoms on the surface
of the steel, and accelerated the reaction of cathodic depolarization.
It increased the corrosion rate of the steel [26].
The values of themaximumpit depth were bigger in the soil with
SRB than those without SRB, which indicated that SRB enhanced the
pitting tendency (Fig. 6). When the chloride ion concentration was
0.05%, no pitting was observed on the steel in the soil with SRB.