Pipelines for Electrolytically Conducting Liquids

Interference measurement/object Interference measurement +At/ values mV telephone cable 60.0 

As in the case of corrosion at the insulating connection due to different potentials caused by cathodic protection of the pipeline, there is a danger if the insulating connection is fitted between two sections of a pipeline with different materials, e.g., mild and stainless steel. The difference between the external pipe/soil potential is changed by cell currents so that the difference between the internal pipe/ medium potential has the same value, i.e., both potential differences become equal. If the latter is lower than the former for the case of free corrosion, the part of the pipe with the material that has the more positive rest potential in the soil is polarized anodically on the inner surface. The danger increases with external cathodic protection in the part of the pipeline made of mild steel. 

In the previous case, it was a question of a type of bimetallic corrosion without electrical contact between the metals involved. The process initially is difficult to understand it is, however, easy to understand if one considers it as a battery with an external short circuit caused by an electrolyte behaving in the same way. The results of measurements on a model and the action of cathodic protection are described in Ref. 23. 

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