Geophysical surveys, specifically electrical surveys, can provide data to help prevent or diagnose corrosion of underground pipelines and other structures, as well as for design of electrical grounding grids.

Metals have natural electrical energy levels or potentials, ranging from the noble to base metals.  When dissimilar metals are connected by a conductor, the electrical potential difference will drive current flow.  The current is carried by electrons (e^-) leaving the base or anodic metal.  Loss of electrons is oxidation; a process commonly called rusting or more generally corrosion. The flow of electrons and the oxidation reaction on the corroding anode makes a galvanic corrosion cell. In the Earth, galvanic corrosion cells occur when dissimilar metals lie in a conductive soil, or similar metals lie in inhomogeneous soil.  Galvanic corrosion cells are less likely to develop for similar metals in uniform soils, and for dissimilar metals in a resistive soil.  Thus, knowledge of in-situ soil electrical conductivity (the exact inverse of resistivity) can provide a qualitative indicator of the corrosion potential for underground structures.

Corrosion may also occur where there are artificially introduced DC electrical currents in the Earth (stray currents). These may occur near electric rail lines, certain machinery, or cathodic protection systems.  If the Earth current jumps into a metal structure, the structure will be anodic, and corrode, anywhere that the current leaves. Note that by common sense convention, the positive direction of current flow is in the opposite direction of the movement of negatively charged electrons.  As with galvanic corrosion, stray current (or electrolytic) corrosion is allowed by conductive soils. Since active corrosion involves current flow in the Earth, spontaneous potential (SP) geophysical surveys can locate areas where corrosion may be occurring in the subsurface.  In addition, the measured polarity (direction of current flow) can help in determining whether the corrosion is galvanic or electrolytic, and where the anode and cathode lie

Corrosion on Brass Rusting Steel Pitted Steel Pitted Copper

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Electrical geophysics methods are also useful for detecting holidays, or holes in corrosion-resistant underground pipeline and tank coatings.  An electrical signal applied to the protected structure leaks out through the holiday, and allows precise pin-pointing of the exposed metal. Utilities whose precise location is not known can be readily located and traced using a variety of utility detection and mapping methods.

Measurements of the local soil resistivity, and variations in resistivity, are also critical for the design of electrical grounding grids.  The soil resistivity dictates how much surface area of grounding wire must be in contact with soil to provide a low enough contact resistance for safe grounding of equipment in power plants, substations, wind farms, etc.  Both the IEEE (81-1983) and ASTM (G57-95a) have standards for determining and reporting resistivity.