Attenuation equations have been given1 which describe the variations in current, potential, cathodic current density along a long uniform structure being protected by drainage from a single point. A later paper2 has described equations derived from these which described the conditions along a structure having a finite number of smaller drainage points. Further modification of the assumptions, including the consideration of an infinite number of small drainage points, leads to further simplification of the resulting equations. This is of particular interest because it is the type of installation employed in the use of magnesium anodes.
The equations derived correlate well with actual experience, which has shown that the total current requirements are usually much smaller with distributed drainage than with the concentration associated with the use of rectifiers. Most of the excessive current used by the rectifier type of protective system is attributable to the wasted power expended...
