What Does Soil Resistivity Mean?
Soil resistivity is the property of the soil that impedes or resists the flow of electric current through it.
Soil resistivity determines the flow of electric current that promotes corrosion in pipes and structural parts buried under the soil. Hence, it determines the type of protective coating required and cost involved. Variation in soil resistivity is also a problem area needing regular monitoring. The higher the soil resistivity, the lower the risk of corrosion.
Corrosionpedia Explains Soil Resistivity
Soil resistivity is the measure of soil's capability to oppose, resist and reduce the flow of electric current through it. It varies across its depth and breadth due to changes in composition, moisture content and temperature. With higher moisture, the resistivity reduces to a certain minimum value. Presence of soluble salt along with moisture also reduces resistivity. While constructing a grounding station, moisture and salt are added to the soil, based on the measured value of resistivity.
Due to its variability, soil resistivity monitoring, measurement and control is vital for proper functioning of electrical power systems and their components, such as grounding stations and lightning protection systems. A higher resistivity value can affect the stability of power systems, and thus the safety of workers and users of electrical equipment. Earth becomes the return conductor in certain single-line systems and earth resistivity can greatly affect system performance in such cases.
Power systems require a number of grounding stations for ensuring reliability and safety. Soil resistivity and the variability due to change in moisture content and temperature are considered during the design stage for pipelines and structures buried in the soil. Lower values of resistivity can aggravate corrosion on the outer surface of pipelines and additional costs are incurred in applying a suitable protective coating on the outer surface prior to laying of the pipes. Corrosion of buried pipelines and structures can severely affect the capability of the system, and eventually result in costly failures and repairs.