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Cathodic Protection
Cathodic protection is one option for protecting an underground storage tank (UST) from corrosion. There are two types of systems for cathodic protection:
- Sacrificial anode
- Impressed current
Sacrificial anodes can be attached to a coated1 steel UST for corrosion protection (see below, left and center). Sacrificial anodes are pieces of metal more electrically active than the steel UST. Because these anodes are more active, the corrosive current will exit from them rather than the UST. Thus, the UST is protected while the attached anode is sacrificed. Depleted anodes must be replaced for continued corrosion protection of the UST.
An impressed current system uses a rectifier to convert alternating current to direct current (see below, right). 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.
Federal regulations require that the cathodic protection systems installed at UST sites be designed by a corrosion expert. The system must be tested by a qualified cathodic protection tester within six months of installation and at least every three years thereafter. You will need to keep the results of the last two tests to prove that the cathodic protection is working. In addition, you must inspect an impressed current system every 60 days to verify that the system is operating. Keep results of your last three 60-day inspections to prove that the impressed current system is operating properly.
This is an illustration of cathodic protection by using sacrificial anodes.
This is an illustration of cathodic protection by using sacrificial anodes.
This is a line diagram of cathodic protection by impressed current.
1 The coating must be of a suitable dielectric material (i.e., a coating that electrically isolates the UST from its environment and meets applicable industry codes). An asphaltic coating is not considered a suitable dielectric coating.