Level 1: All tanks are coated with a high-quality dielectric coating.
Level 2: The tank is shipped complete with isolation devices to protect it from other underground structures, such as metal piping, hold-down straps, submersible pumps, etc.
Level 3: The final measure of protection is the anodes. The anodes are made from metals that are more electrically active and, therefore, will corrode preferentially to steel. For an sti-p3 tank, the anodes are zinc or magnesium.
STI’s recommended practice “sti-P3 Specification and Manual for External Corrosion Protection of Underground Steel Storage Tanks” is available for purchase. This specification provides straightforward, step-by-step guidelines for testing the cathodic protection of an sti-P3 tank.
An impressed current system is tested differently than an sti-P3® tank, because the current output of an impressed current system is much greater than that of an sti-P3® tank. In most cases, instant-off readings must be used to account for IR drop. Details of this type of testing are taught in STI’s Cathodic Protection Certification class.
STI’s recommended practice R972 Adding Supplemental Anodes covers basic testing and troubleshooting tests. Based on test results, it may be possible to retrofit the tank with supplemental anodes and R972 provides retrofit instructions. You must follow all state and local regulations when adding supplmental anodes.
Cathodic protection test results do not indicate whether or not a tank is leaking. Cathodic protection testing measures only whether the CP system meets the required minimum readings. Monthly monitoring, leak detection and tightness tests must be performed to verify that a tank is tight.