Cathodic Protection Training Course



Module 13

Cathodic protection and corrosion currents

Current paths and C.P. circuits.

I designed the three nail experiment as a way to understand the way that currents actually work in cathodic protection.

When carried out in a plastic tray this shows a contained circuit in a similar way to studying the currents in a dry cell battery

When carried out in a metal tray, the energy source can be connected in the same way but the tray can also be energised from many sources and through timers.

In cathodic protection work we are confronted with a return path through mass earth that is sometimes refered to as 'ground' and is infinite in energy variables.

The earth has magnetic values that are changing and sunspot activity results in surges of energy in the ground that equalise in accordance with laws of physics.

When we make 'pipe-to-soil potential measurements' one side of the meter is connected to the copper/copper-sulphate ground contact electrode and the other side of the meter to a span of the pipeline metal itself. The stray currents in the ground itself are a component of the measuring circuit.

The currents resulting from each of the corroson cells on a span of pipeline are in micro-amps and pass through the least line of resistance to coplete the corrosion circuit. This generally does not affect the potentil of the ground above that is contacted by the copper/copper-sulphate electrode.

Realising this massive problem I invented the Alexander Cell that makes it possible to measure actual corrosion currents.