Induction effects of 2-D structures on buried pipelines

The implementation of cathodic protection systems is very complicated since many factors can contribute for current flowing off the pipe. The design requires the characterization of the parameters impacting the corrosion process, such as soil resistivity, size of the pipe and quality of the coating. In the present paper, we study the effect of geomagnetic fields on the pipe-induced currents considering it as an additional cause of corrosion. A theoretical method previously implemented to model the currents induced on pipes embedded in homogeneous soils indicated a dependence between the intensity of the currents and the electrical resistivity of the soil, and predicted that a drainage of current through the pipe would occur at zones of shallow electrical discontinuities. Here, we present another method for the calculation of the induced currents that allows us to consider also multilayered structures and lateral discontinuities in the Earth resistivity. Applying this method, we quantify the currents induced in pipelines embedded in different bidimensional structures in order to obtain an estimation of the effects produced by the presence of such kinds of terrains. We then applied this method to model measured data. Field work was performed along a 200 km-route of a pipeline system. In this zone, the pipe-to-soil potential was measured at different sites and a geophysical study was made to determine the discontinuities in soil resistivities. We obtained a correlation of the measured currents and soil resistivity consistent with the theoretical predictions. This fact strongly suggests that in zones of deep high resistive contrast, the current circulating in the pipes increases, being the consequent risk for the coating and the cathodic protection adjusting, not only dependent on the resistivity of the ground-bed but also on this deep structure.