Soil resistivity relates to an increase in corrosion activity and therefore dictates the type of cathodic protection designed to protect metallic structures found in various environments. Common applications for cathodic protection are steel water or fuel pipelines and steel storage tanks; steel pier piles; ship and boat hulls; offshore oil platforms and onshore oil well casings; offshore wind farm foundations and metal reinforcement bars in concrete buildings and structures.
And how do we test the soil? In-situ soil resistivity testing is performed using the Wenner 4-Pin Method in accordance with ASTM G57. This test method involves the use of four metallic pins driven into the soil in a straight line at equidistant spacing. A ground resistance tester is used to discharge alternating current into the soil from the two outer pins. The current creates a voltage gradient in the soil proportional to the average resistance of the soil. The voltage drop between the two inner pins is measured, and the resistance of the soil to a depth equal to the pin spacing is calculated by the meter using Ohm’s Law. This gives us a snapshot of the level of corrosion beneath the surface, guiding us to the best Cathodic Protection design.