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Sep.01.2026
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Corrosion is one of the primary causes of failure in buried grounding grids. For a grounding system designed to serve for 30 to 40 years, the corrosion rate of conductors and connection points in the soil directly affects its actual service life.
Effective corrosion protection requires a comprehensive approach covering corrosion mechanisms, material selection, installation techniques, and inspection and maintenance.
The corrosion of buried metal grounding conductors is essentially an electrochemical process. Metal loses electrons and dissolves into the surrounding soil electrolyte, while moisture and dissolved salts provide an ionic conduction path. Oxygen and other depolarizing agents sustain the electrochemical reaction.
In addition to uniform corrosion, several types of localized corrosion require particular attention.
Different sections of a grounding conductor may be exposed to different oxygen concentrations in the soil. Areas with lower oxygen concentrations can become anodic regions, resulting in accelerated localized corrosion.
This is particularly common in grounding grids where backfill is poorly compacted or where water accumulates locally.
When dissimilar metals with different electrochemical potentials are directly connected in a moist soil environment, they can form a galvanic cell. The more active metal acts as the anode and undergoes accelerated corrosion.
Therefore, direct connections between incompatible metals should be carefully evaluated during grounding system design and installation.
Stray currents can be particularly destructive in areas near electrified railways, DC power systems, or other sources of stray electrical current.
When stray current enters or leaves a grounding conductor through a localized area, severe electrolytic corrosion may occur at the current discharge point. In extreme cases, localized corrosion can cause perforation within only a few years.
Soil corrosivity should therefore be evaluated comprehensively based on parameters such as soil resistivity, moisture content, pH value, and redox potential. Low-resistivity, highly acidic, and high-salinity soils generally represent more aggressive corrosion environments.
The key to material selection is matching the material's corrosion resistance and corrosion allowance to the required service life.
Hot-dip galvanized steel relies on the sacrificial-anode protection of zinc. Because zinc has a more negative electrochemical potential than iron, the zinc coating preferentially corrodes and protects the underlying steel.
The thickness and quality of the zinc coating directly affect the service life. In highly corrosive soils, enhanced or heavy-duty galvanizing should be considered according to the project requirements.
Copper and copper alloys generally have good corrosion resistance in a wide range of soil environments. A relatively stable protective surface film can form under suitable conditions, resulting in a low corrosion rate.
These materials are therefore suitable for grounding systems requiring long service life and high reliability.
Copper-clad steel combines the electrical conductivity and corrosion resistance of copper with the mechanical strength of steel. It is widely used where both long-term durability and mechanical performance are required.
For copper-clad steel conductors, copper layer thickness, continuity, and bonding quality are critical quality parameters.
Corrosion allowance should also be considered during the design stage. Based on the estimated corrosion rate and required service life, sufficient allowance should be incorporated into the conductor cross-section. Although this requirement may be included in engineering specifications, it is sometimes overlooked during actual implementation.
Connection points are among the most vulnerable areas of a grounding grid.
Exothermic welding can produce a metallurgically bonded connection with excellent electrical and mechanical continuity. However, the welded area should still be properly cleaned after welding, and appropriate corrosion protection should be applied where required.
For arc-welded lap joints, the weld zone and heat-affected area may be more susceptible to corrosion due to thermal effects and residual stresses. These areas require additional corrosion protection.
Backfilling directly affects the long-term condition of a buried grounding grid.
Fine soil should be placed around the grounding conductor in layers and properly compacted to ensure uniform contact between the conductor and surrounding soil.
Construction debris, bricks, stones, and other foreign materials should not be mixed into the backfill. Poorly compacted areas and voids can create differences in oxygen concentration and moisture distribution, increasing the risk of localized corrosion.
When different metals are connected within the same grounding system, appropriate transition components, protective measures, or electrical isolation should be considered according to the system design.
The objective is to prevent uncontrolled galvanic corrosion and avoid creating localized weak points within the grounding network.
Periodic grounding resistance measurements are useful for monitoring the overall performance trend, but resistance testing alone cannot fully determine the physical condition of a grounding grid.
Where necessary, continuity testing should be combined with grounding resistance measurements to evaluate the integrity of the grounding network.
Historical test data should also be recorded and compared over time. A gradual increase in grounding resistance may indicate deterioration of grounding conductors, connection points, or surrounding soil conditions.
For important grounding systems, inspection wells and disconnectable test points can be incorporated into the original design. These facilities make it easier to perform sectional testing and assess the condition of different parts of the grounding grid during future maintenance.
Corrosion protection is not a single construction procedure. It is a full-life-cycle engineering process covering design, material selection, installation, inspection, and maintenance.
A high-quality grounding system should not only achieve the required grounding resistance when it is first commissioned, but also maintain reliable electrical continuity and mechanical integrity throughout its intended service life.
By properly evaluating the soil environment, selecting suitable grounding materials, controlling connection and backfilling processes, and establishing a systematic inspection program, the long-term reliability of buried grounding grids can be significantly improved.
Reliable grounding starts with the right design—and long-term reliability depends on controlling corrosion from the very beginning.
