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2. Factors Affecting the Rate of Anchor Corrosion
2.1 Many factors affect corrosion activity on guy anchors in direct contact with soil. Generally, the corrosivity of the soil, the magnitude of electromotive force (emf) between dissimilar metals, and the relative size of the anode to the cathode are primary factors. Stray direct current from an outside source can also contribute to rapid corrosion.
2.2 Soil corrosivity is complex, but is generally more severe as: soil resistivity decreases below 10,000 ohm/cm, soil pH is below 3 or above 9, and redox potential (a measure of microbiologically influenced corrosion potential) decreases below 100 mV. The presence of chlorides, sulfides, salts, organic materials, different oxygen levels, poor drainage, different soil types and moisture content are among the factors that can contribute to corrosivity. Factors can vary seasonably. For example, soil resistivity generally decreases as temperature rises. Also, site specific activities such as doping the soil to enhance grounding can increase soil corrosivity.
2.3 Lower soil resistivity provides a more conductive environment for the flow of current. With regards to resistivity, table 1 illustrates a classification that can be used to indicate corrosivity of soil.
Table 1. Soil Resistivity Classification
| Resistivity in ohm/cm |
Category |
| 0-2000 |
Very corrosive |
| 2000-5000 |
Corrosive |
| 5000-10,000 |
Moderately corrosive |
| 10,000-25,000 |
Mildly corrosive |
| Over 25,000 |
Progressivly less corrosive |
2.4 Differences in the energy potential of various metals have been documented in the Galvanic Series (see table 2). Metals listed higher on the series are more active and will release energy to ones below. Non-uniform conditions along the surface of a metal can also cause different energy potentials. For example, the portion of an anchor embedded in concrete typically has lower energy potential than the portion exposed to soil.
Table 2. The Galvanic Series
| Metal |
Approximate Volts to CuCuSo4 |
| Magnesium Alloy |
-1.60 |
| Zinc |
-1.10 |
| Alluminum Alloy |
-1.05 |
| Mild Steel (Clean & Shiny) |
-0.50 to -0.80 |
| Mild Steel (Rusted) |
-0.20 to -0.50 |
| Cast Iron |
-0.50 |
| Lead |
-0.50 |
| Mild Steel in concrete |
-0.20 |
| Copper, Brass, Bronze |
-0.20 |
| Mill Scale on steel |
-0.20 |
| Carbon, Graphite, Coke |
+0.30 |
General | Factors Affecting the Rate of Anchor Corrosion | Conditions that Require Corrosion Control Measures | New Guyed Tower Procedures | Corrosion Control Measures
Guy Anchor Maintenance Procedures | References
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