Galvanic and Impressed Current Anodes
Cathodic protection engineers take advantage of this process, and design systems where anodes are linked to steel structures to extend the lifetime of the structures. Galvanic cathodic protection is often used for storage tanks, smaller ships and bridges. It is a more simple system than an impressed current cathodic protection system. Installation, inspection and monitoring are simple for trained staff, and stray current and over-protection are unlikely.
A sacrificial anode must have a electrical potential at least 0.2V more negative than the metallic structure in order to be effective. Typical materials for galvanic anodes are zinc, aluminum and magnesium. These 3 metals are among the most anodic metals in the galvanic table, and all are more anodic that any type of steel.
Impressed current cathodic protection (ICCP) systems, though more complex than galvanic systems, provide several advantages. Because of the increased flexibility in anode materials, the ICCP designer can select anodes that will last longer. Also, the external power source provides greater control and monitoring over the entire system. Insufficient or too much current can be detected and changed after installation to ensure the appropriate amount of protection is being delivered.
Because of the greater flexibility and control, ICCP systems are often used on larger projects. Gas and oil pipelines, large ship hulls, reinforced concrete and seawalls are some of the many structures that are protected with ICCP systems.