The Corrosion Cycle

In order for corrosion to exist, there has to be four things present:

• A cathode
• An anode
• An electrolyte
• A mechanical path between the cathode and anode

After two years in the industry, I just realized that the test station I make in my head is kind of incomplete because of the fourth ingredient: in my head, I forget the mechanical pathway needed for the sacrificial anodes to connect to and protect the steel substructure.

Oops.

Hopefully the people in the field are better aware that the anode lead wire must somehow connect to one of the test leads run up from the pipe/tank/what-have-you. This could be done by:

1. Putting the two wires on the same terminal
2. Connecting the two terminals via bond strap
3. Connecting the two terminals via shunt

These are stated in the order of least preferable to best practice. Putting the two wires on the same terminal closes the mechanical connection so that the electricity is in a closed circuit, and the cycle of corrosion is completed so we can draw the electrons off of the anode instead of the steel. But it takes time and effort to remove them for testing.

Ideally, between the "test lead" terminal and the "anode" terminal you have a shunt, which makes for easy testing of the voltage drop.