Many new and recently installed underground steel tanks such as the STIp3 come with cathodic protection. Cathodic protection systems require periodic maintenance and testing to ensure that they are functioning properly.
Electrical currents flowing from a metallic structure, such as a steel tank, into the ground causes corrosion. Cathodic protection is a process that redirects this flow to prevent corrosion.
There are two types of systems for cathodic protection: Galvanic - Sacrificial anodes are installed at each end of a coated steel tank for corrosion protection. Sacrificial anodes are pieces of metal, a softer metal than the steel tank (either zinc or magnesium) which are more electrically active than the steel UST. Because these anodes are more active, the corrosive current will exit from them rather than the UST. This allows the electrolysis of the soil degrade the sacrificial anode as opposed to the steel tank. Therefore, the UST is protected while the attached anode is sacrificed. Depleted anodes must be replaced for continued corrosion protection of the tank. Impressed current systems use rectifiers to convert alternating current to direct current. This current is sent through an insulated wire to the anodes, which are special metal bars buried in the soil near the UST. The current then flows through the soil to the UST system and returns to the rectifier through an insulated wire attached to the UST. The UST system is protected because the current going to the UST system overcomes the corrosion-causing current normally flowing away from it.