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Table 14. Types of Soils Listed in Order of Water Retention Capacity (Corrosion Doctors, 2007)

Soil Type

Sand Loamy sand Sandy loam Sandy clay loam Clay loam Loam Silty loam Silt Silty clay loam Silt clay Clay

Characteristic Low

Water Retention Capacity

High

Soil Parameters

Several approaches have been used for categorizing the corrosiveness of soils to aid in anticipating the degree of corrosion attack on buried pipe. Corrosivity ratings based solely on soil resistivity are shown in Table 15. Soils are rated from “essentially noncorrosive” to “extremely corrosive.” A more detailed corrosivity scale compiled by the American Water Works Association for cast iron buried in soils is listed in Table 16. This table assigns points to various soil parameters including resistivity, pH, reduction/oxidation potential, presence of sulfides, and degree of moisture. Protective measures are recommended for cast iron pipes if the total points for a particular soil equal or exceed 10. Not all parameters have equal importance. For example, soil pH is important only if it falls below 4 or is greater than 9, which is relatively uncommon.

>20,000

Essentially noncorrosive

10,000 to 20,000

Mildly corrosive

5,000 to 10,000

Moderately corrosive

3,000 to 5,000

Corrosive

1,000 to 3,000

Highly corrosive

<1,000

Extremely corrosive

Table 15. Corrosivity Ratings Based Upon Soil Resistivity

Soil Resistivity, Ohm·cm

Corrosivity Rating

Alternative Underground Propane Tank Materials, Phase II—Final Report

25

September 2009 Battelle and Lincoln Composites

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