Page 420 - Corrosion Engineering Principles and Practice

388 C h a p t e r 1 0 C o r r o s i o n i n S o i l s a n d M i c r o b i o l o g i c a l l y I n f l u e n c e d C o r r o s i o n 389

Basis for
Category Classification Example(s) Comments
Family Differences in Clayey oxidic Plants generally
textural classes, isothermic Typic react in a similar
mineralogy, Kandihumult manner to the same
acidity, and soil family.
temperature.
Series Differences in Paaola Usually named after
texture. the location where
the soil was first
described.

TABLE 10.2 (continued)

10.2.2 Soil Parameters Affecting Corrosivity
Several variables are known to have an influence on corrosion rates
in soil; these include water, degree of aeration, pH, redox potential,
resistivity, soluble ionic species (salts), and microbiological activity.
The complex nature of selected variables is presented graphically in
Fig. 10.2 [2].

Type of soil
Sulfate
reducing
Degree of aeration Anaerobic conditions bacteria
(SRB)
Drainage Moisture Alkaline species
groundwater
Weak acids
Resistivity pH Total acidity Strong acids
Ionic species Organic acids
Inorganic acids
Rate of Corrosion Cathodic reaction

Passive film formation
and breakdown Sulfides

Amount of dissolved oxygen
FIGURE 10.2 Relationship of variables affecting the rate of corrosion in soil.
For simplicity, only the MIC effects of sulfate reducing bacteria are shown.