local regions and then spread over the whole surface. EDX analysis
results in Table 4 show that the sulfur content of the corrosion products
buried in the soil with SRB was much higher than that without
SRB. It indicated that FeS existed in the corrosion products, which
enhanced the tendency of pitting corrosion of the steel. The corrosion
products formed on the steel in soils containing 3.0% chloride
ions with SRB contained much higher amounts of Mn and Si, and
lower amounts of S and Fe, which indicated that the pitting corrosion
commenced from the vicinity around inclusions containing
the above elements.
4. Conclusions
1. Amounts of SRB ranged from 23000 to 35000 cell/g soil in soils
containing different chloride ion concentration. Chloride ions
had no significant effects on the survival situation of SRB. The
number of SRB in soils with chloride ions was higher than that
without chloride ions.
2. The corrosion potential of stainless steel 1Cr18Ni9Ti moved
towards the negative direction with increasing chloride ion contents
in soils, and the corrosion potential in soils with SRB was
much more negative than that without it.
3. No pitting corrosion for stainless steel 1Cr18Ni9Ti buried in soils
without SRB, but severe pitting corrosion in soils containing
chloride ions above 0.05% with SRB were observed, respectively.
The maximum pitting depth increased with increasing chloride
ion contents in soils. It indicated clearly that the presence of SRB
might enhance the pitting susceptibility of the stainless steel
in soils containing chloride ions. In other words, the susceptibility
to the pitting corrosion of the steel was enhanced by the
combined actions of SRB and chloride ions.
4. Onecapacitive loop with a large radius was observed for stainless
steel 1Cr18Ni9Ti in soils without SRB and two capacitive loops
for that with SRB.
5. There was only one time constant for Bode plots of the stainless
steel in soils containing 3.0% chloride ions without SRB. A single
capacitive loop with a large radius was observed for Nyquist plot
of the steel in soils containing 3.0% chloride ions with SRB after
burying for 1 day and two loops after burying for 4 days.
6. Many pitting holes were clearly observed on the surface of the
steel buried in soils containing 0.5% chloride ions with SRB. Sulfur
content of the corrosion products on the surface of the steel
formed in soils with SRB was much higher than that without SRB.