Effect of Geomagnetic Variations on the Cathodic Protection of Pipelines.

During the winter of 1982/83, the variations of the geomagnetic and telluric field, the pipe flow rate and the pipe-to-ground potentials were continuously recorded at three measurement stations along two long-distance gas pipelines from Waidhaus (near the Czech border) to Nuernberg. A possible explanation for the variations of the pipe-to-ground potential is provided by a combination of two extremal models, in one of which the pipeline is regarded as perfectly insulated and this as an equipotential line in a varying geoelectric field while in the other it is regarded as a high-conductivity channel for telluric currents. An estimate of the time period during which the cathodic protection potential is exceeded yielded a value of at most two day per year, which constitutes a negligibly small threat to the corrosion protection.