Stray Current Corrosion Prevention

The best method to prevent stray current corrosion is to eliminate or reduce the stray current. In other words, act on the source, instead of acting on the consequences. This can be accomplished by increasing the global circuit resistance in one of many ways.

Cathodic protection is based on bringing the galvanic potential of the metal to a level where the anodic reactions are impossible for the given circumstances. This is achieved by virtue of an external current that reduces or inverses the anodic current. The required amount of current is directly related to the unknown dimensions of the anodic zones. The total current needed for protection can be estimated, but is not an adequate protection criterion. Therefore, metals are considered to be protected in a given environment when the potential of the structure is maintained more negative than a given value or when the potential is altered by a predefined amount.

Traditional cathodic protection techniques (using sacrificial anodes or impressed current/voltage anodes) could ensure complete corrosion protection (metal potential minimal at -0.85V to Cu/CuSO4 electrode) or could eliminate the stray current corrosion.

When the sources of stray currents are accessible, current drainage techniques can be implemented. This means that the structure that suffers from stray current corrosion is connected to the negative pole of the DC source that generates the stray current. This metallic connection must have a lower resistance than the alternative earth return path.

Moreover, this connection is made unidirectional, such that current can only flow from the buried structure to the negative pole of the DC source (for traction, the negative pole of the drain is connected to the rails). Stray currents that entered the structure will then prefer this connection to return to the generator, instead of the electrolyte (the soil). When this connection contains a DC source that drives the current to the generator, the technique is called "forced drainage". The amount of current that is drained from the protected structure can be controlled either by varying the boosting DC voltage or by changing the resistance of the direct connection. This implies that any degree of protection can be obtained.

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