Galvanic System Equipment
In this type of application the naturally occurring electrochemical
potentials of different metals are used to provide protection.
Sacrificial anodes are coupled to the structure under protection and conventional current flows from the node to the structure as long as the anode is more “active” than the structure. As the current flows, all the corrosion occurs on the anode which “sacrifices” itself in order to offer protection from corrosion to the structure.
The galvanic series for common metals is shown below Table. On the active side of the drawing the metals such as zinc, aluminum and magnesium appear. These metals and their alloys are the most commonly used sacrificial anodes
- Magnesium Anode
Magnesium Anode is used for Temporary protection of buried pipelines, protection of well coated buried pipelines, and protection of small marine structures, “Hot spot” locations for buried & Submerged steel structures, Protection of well coated buried pipelines, internal protection of water tanks, pipeline casing sleeves. Suitable for use in soils, mud, fresh water, brackish water and sea water. Magnesium anodes are classified into two categories in terms of chemical composition and type of application:
1) Standard Magnesium Anode (AZ63)
2) High potential Magnesium Anode (M1C)
- Zinc Anode
Zinc has been used as a sacrificial anode material in seawater since 1824. Modern zinc anodes used for Cathodic Protection are cast from high purity zinc (99.99%) alloyed with aluminum and cadmium with limitations on the level of lead, iron and copper.
Typical applications include, submarine pipelines, ballast tanks, offshore structures, storage tank internals, quay walls, water tanks, marine applications and ships hulls.
Zinc anodes are classified in terms of chemical composition and application type in two categories: 1) Zinc Sea Alloys (Type I) designed for use in seawater.2) Zinc standard alloy (Type II), which is formulated into fresh water and soil.
- Aluminum Anode
Aluminum alloy anodes have been formulated primarily for use in seawater. Alloys are also capable of achieving high output capacity in mud and brackish water of resistivity up to 150 Ohm.cm. Aluminum anodes have approximately three times the capacity of Zinc alloys.