What Does Sacrificial Protection Mean?
Sacrificial protection is a corrosion protection method in which a more electrochemically active metal is electrically attached to a less active metal. The highly active metal donates electrons to replace those which may have been lost during oxidation of the protected metal. This reverts the protected metal back to its original form, and thereby prevents it from corroding.
Corrosionpedia Explains Sacrificial Protection
A typical sacrificial protection is where a more reactive metal is used as a sacrificial anode by attaching it to steel pipes or pump bodies. The iron becomes a cathode which does not corrode, while the anode corrodes to provide the desired sacrificial protection. The sacrificial metal must however be replaced periodically as it is consumed, otherwise, the protected metal starts corroding.
The sacrificial process occurs when the more reactive metal, which may be attached using copper wires, donates its electrons to the iron and replaces those lost when iron has oxidized, thereby reverting the iron back to its original state.
Materials used as sacrificial anodes are either purely active metals, such as magnesium or zinc, or the alloys of either aluminum or magnesium specifically developed to be used as sacrificial anodes. The sacrificial protection may be provided by using the anodes, usually supplied with cast-m straps or lead wires. The lead wires can be attached to the structure using mechanical or welded connections, and should have low resistance and insulation to prevent them from corroding or becoming damaged mechanically.
Sacrificial protection is used for corrosion protection in:
- Underground tanks
- Water heaters
- Above-ground tanks
- Hulls of ships
Advantages of sacrificial protection include:
- Low cost
- Provides protection without power requirement
- Does not require maintenance
- Simple installation and operation
- Periodic replacements of the anode
- Increased noise level from the anodes
- Current output cannot be regulated
- Periodic replacement costs, especially in ships since they must be dry docked