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Cathodic Protection- Impressed Current Systems


Impressed current systems use an outside source of power to drive the current from the anodes to the cathode. This source can be solar power, batteries, DC generators or 60 Hz alternating current (AC) converted to DC via a rectifier or other device. The most common impressed current systems consist of an anode cluster (also called a "ground bed"), which can be in one location or distributed around the protected structure, powered by rectified AC power.

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There are many different materials to choose for impressed current anodes. Early applications used old railroad steel rails buried in the ground for the protection of buried pipelines. Anode materials include graphite rods, silicon-iron alloys and lead-silver alloys. More recent technology includes platinized titanium or niobium rods and disks, conductive graphite impregnated polymer wires, conductive paints and grouts and mixed metal oxide coatings on titanium substrates of various shapes. The latest anode technology incorporates thermal sprayed zinc and thermal sprayed titanium. These are used particularly on concrete substrates as surface conforming anodes.

Impressed current systems are commonly used where the current requirements for corrosion protection are high and where the driving voltage is greater than what can be obtained with galvanic systems. These systems are more accurate and can be controlled to deliver just enough protective current to the structure. Their disadvantage lies in that they require more maintenance and consume power.