MIL-HDBK-1005/16
characteristics, other soil tests are needed to determine
characteristics that affect corrosion performance.
12.1.1.1 Soil Testing. A number of soil characteristics will
have a direct effect on the corrosion performance of certain
materials that are buried in the soil. There are a variety of
opinions expressed regarding the interpretation of soil data;
however, most authorities generally agree with the information
presented in Table 21.
These data are easily determined during the
geotechnical assessment of the plant site. From these results,
the type of cement required can be determined (for sulfate
resistance). In addition, the soil resistivity may be used to
determine the need for corrosion protection for buried metallic
pipelines, such as ductile iron or steel pipe. Additional
information on the requirements for cathodic protection and
protective coatings is discussed in par. 12.3.
Table 21
Critical Soil Parameters
Parameter
Criteria
Sulfates
Moderate sulfates: 0.10-0.20% in soils; 150-
1,500 ppm in water. Requires <8% tricalcium
aluminate (Type II cement).
High sulfates: >0.20% in soils; >1,500 ppm in
water. Requires <5% tricalcium aluminate (Type
V cement).
Presence of chlorides can cause low soil
resistivity, <1,500 ohm-cm. The use of a
barrier coating is generally required if the
chloride levels are >200 ppm.
pH
pH 5 or greater: no additional protection; pH
<5 use barrier coating on concrete, coatings
and cathodic protection on ferrous metals, or
nonmetallic piping material.
Resistivity
0-1,000 ohm-cm: Extremely corrosive.
1,000-3,000 ohm-cm: Very corrosive.
3,000-10,000 ohm-cm: Moderately corrosive.
10,000-30,000 ohm-cm: Slightly corrosive.
>30,000 ohm-cm: Noncorrosive.
12.1.2
Submerged Exposures. In a wastewater treatment plant,
there is a considerable amount of concrete and metal that is
partially or continuously submerged in wastewater. In most
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