The corrosive properties of soil towards underground structures is a widespread problem all over the world. Anything made from common iron formulas such as ductile iron or gray iron can be a problem. Water lines, natural gas or crude oil lines, or any other buried structures are all subject to the damaging effects of the soil around them.
The soil itself is a complex heterogeneous mixture of minerals, organics, water, air, and gases. All of these components work together to create an environment which may be hostile to whatever is exposed to them. This makes regional generalizations about soils difficult because the combination of factors can vary widely, even in the same area.
For these reasons, soils should be analyzed for corrosion potential wherever structures are expected to be buried for long periods of time.
The American Water Works Association (AWWA) and the Ductile Iron Pipe Research Association (DIPRA), have designed a 10 point system for soil evaluation. This is based on the result of five different soil tests and observations:
- Soil Resistivity. Low soil resistivity will make the soil a better electrolyte for corrosion.
- pH. Soils with a pH below 4.0 are considered acidic, making them a good electrolyte. Also, soils with a high pH over 8.5 usually have high concentrations of dissolved salts, giving them lower resistivity.
- Oxidation-Reduction (REDOX) Potential. Redox potential is a measure of soil aeration. Low results suggest the soil is anaerobic and can support corrosive sulfate-reducing bacteria.
- Sulfides. The presence of sulfides usually indicates the presence of sulfate-reducing bacteria.
- Moisture. Better referred to as general drainage characteristics. Poorly draining soils will naturally support a more aggressive environment than well drained drier soils.
For each soil analyzed, the results are assigned points based on their influence towards corrosivity. If the sum of the results is 10 or higher, the soil is considered corrosive, and will likely need protective measures to prevent failure.
Not knowing the potentially damaging environment that you may be exposing buried structures to can add significant costs and repairs to any project. Sterling Analytical is qualified to perform the full battery of tests and observations and evaluate your soil samples for corrosion potential.