Abstract
Various sources of fluctuating electromagnetic fields produce electric fields and currents in buried pipelines, which interfere with the pipeline infrastructure. Among these sources are power lines with a known single frequency (50 or 60 Hertz, Hz) and the natural geomagnetic field with variations in the frequency range from millihertz (mHz) to few Hz, which produce telluric currents in the pipelines.
In this paper the analytical approach to the problem of the induction by external sources of variable frequency in an infinitely long multi-layered cylinder, representing the pipeline, is extended to include the conductivity contrast between the soil, in which pipeline is buried, and the air or sea water above it. The surface conductivity contrast influences the electromagnetic fields and currents depending on frequencies and pipeline electromagnetic characteristics. The mathematical model presented has been applied to the cases of underwater pipelines or pipelines embedded in soils with different conductivities. Modeling results show attenuation of the electric field induced in the pipeline in the case of significantly larger conductivity of upper media for AC and telluric frequencies.
The developed analytical method can also be used for evaluation of ready-made software packages that deal with electromagnetic interference especially for low frequencies.
