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Numerical Corrosivity Scale

The American Water Works Association (AWWA) developed a numerical soil corrosivity scale, applicable to cast iron alloys. The severity ranking by assigning points for different variables. When the points total of a soil in the AWWA scale equals ten (or higher), corrosion protective measures (such as cathodic protection) have been recommended for cast iron alloys. The point system for predicting soil corrosivity according the AWWA C-105 Standard.

Soil Parameter

Assigned Points

Resistivity (ohm cm)

<700

10

700 - 1000

8

1000 - 1200

5

1200 - 1500

2

1500 - 2000

1

> 2000

0

pH

0-2

5

2-4

3

4-6.5

0

6.5-7.5

0

7.5-8.5

0

>8.5

3

Redox Potential (mV)

>100

0

50-100

3.5

0-50

4

<0

5

Sulfides

Positive

3.5

Trace

2

Negative

0

Moisture

Poor drainage continuously wet

2

Fair drainage generally moist

1

Good drainage generally dry

0