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Corrosion of metallic structures arises when an electric current flows from the metal into the electrolyte. The potential difference across the metal-electrolyte interface, the driving force for the corrosion current, can emerge due to a variety of non-homogeneous conditions on either side of the interface such as temperature, pH, humidity, etc. ... in the metal or the electrolyte [1-3].
But metallic corrosion can also be the result of variations in the electric potential within the metal and/or the electrolyte, caused by direct current flowing through them. This corrosion, sustained by external currents (sources) that originally do not belong to the specific anode-cathode couple, is called stray current corrosion. This means that currents generated by anode-cathode couple X are stray currents for another different anode-cathode couple Y.
Two mechanisms bring about stray current corrosion (Figure 1). Current can flow in the metal and cause potential gradients, which is referred to as structure current corrosion. Or the current can flow in the electrolyte and induce potential differences in the electrolyte, which is called earth current corrosion. In most underground situations, those two types of stray current corrosion do exist simultaneously.
In a first approach, the induced corrosion current can be considered as an alternative current (path) for the stray current. Generally, an extra stray current source, sustaining a potential difference Vsc, is present in the corrosion system. This Vsc will drive current around the corrosion circuit, comprising the resistances associated with the structure, the electrolyte and the metal-electrolyte interface. It is obvious that the stray corrosion current is a function of Vsc, the circuit resistances and polarization or coatings that exist at the electrode-electrolyte interface.
On the object of stray current corrosion see also: DC traction, Cathodic protection, Coating, Contour plots, Definition, Detection, Examples, External currents, Historical perspective, Impressed current, Interference, Mechanisms, Modeling. Pipeline, Potential distribution, Prevention, Stray fields and leakage, Transit systems
Study and Evaluation of Stray Current Influences on Cathodic Protection Systems of Buried Pipelines, L. Bortels, ELSYCA - Kranenberg 6 - 1731 - BELGIUM, ELSYCA
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