How to Test Propane Tank Cathodic Protections

Unscrew the porous tip of a copper/copper-sulfate half-cell electrode and fill the electrode with distilled or deionized water. Replace the tip. Some of the copper sulfate crystals in the electrode should dissolve, turning the water blue.

Stand the electrode upright on a clean surface with the porous tip on the bottom. Allow it to sit for 15 minutes so the tip becomes saturated with water.

Set your voltmeter to the "2-Volt DC" scale.

Connect the red test lead of the voltmeter to the tank test point if there is one. If you can't find the test point, attach the lead to an uncoated metallic part of the tank or to an uncoated part of the pipe that's used to fill the tank.

Attach the black lead of the voltmeter to the connector on the top of the electrode.

Place the porous end of the electrode into the earth above the propane tank.

Record the reading on the voltmeter. If you can't get a reading, dig the electrode deeper into the ground or add water to the soil to provide better contact.

Repeat the process at two or three other points around the perimeter of the tank to make sure you get a similar reading. If the readings vary, find the average of the reading. The average reading should be at -0.85 volts or above. A reading of -0.86 or -0.90 volts is considered to be above -0.85 volts, while -0.50 volts would be considered below -0.85 volts. If the reading is below -0.85 volts, the magnesium bar should be replaced.