A method is described for determining the interference which theoretically may be expected on a long structure due to forced drainage on a similar parallel structure. The method is applied to four-inch welded bare steel pipes and variations are introduced to illustrate the effects of:
a) the presence of coatings on the pipes and
b) changes in soil resistivity, longitudinal conductivity of the structures, diameter of the structures, distance to the anode and separation of the structures.
Important conclusions drawn from this study are:
There is no location of the anode at which interference effects are completely nullified. Practical minimum interference is obtained over a wide range of anode location points.
For an anode location within practicable distance from the structure the interference effects can the-orectically best be overcome by a bond each side of the drainage point rather than one bond at the drainage point.
Protective coatings, even those with conductance as high as one mho per kilometer, have very marked effect in reduction of interference current.
Variations in dimensions of structures, separations, soil resistivity, etc., have relatively little effect on interference.
