About Galvanic Corrosion
Cause and Prevention of Galvanic Corrosion in Aluminium
Cause
Four conditions must be present for galvanic corrosion to occur:
o Cathode - the more noble or least active metal. This metal has current discharge properties and will be protected from corrosion by the presence of the anode metal. Cathode examples: copper, gold, silver, nickel
o Anode - the least noble or active metal. This metal has current acceptance properties and will corrode. Anode examples: magnesium, zinc, aluminium
o Electrolyte - the capacity to conduct electrical current through the flow of ions. Electrolyte example: water
o Metallic path - metallic connection conducting electrical current. Other factors affecting the corrosiveness of water are pH, temperature, and oxygen content. Water pH should remain between 6 and 8 to minimize corrosion. Increased temperature and oxygen in water also accelerate corrosion.
Prevention
Five ways to inhibit galvanic corrosion in water systems:
o Cathodic Protection - A sacrificial anode (usually a zinc or magnesium rod) is installed in the system. The material is more anodic in nature than the aluminium and draws the corrosion away from the aluminium. This is a higher maintenance solution as the anode must be replaced periodically.
o Water Condition - Change the water treatment system. Eliminate any chlorine or floating ions and monitor the pH level of the water. Add corrosion inhibitors.
o Material Selection - Change the ratio of dissimilar metals so it is more evenly balanced, or remove the dissimilar metals completely. Use stainless steel components.
o Coatings - Insulate the metals with a protective coating. This is often temporary. The anodizing on our aluminium manifolds usually provides adequate protection, except in severe environments.
o Metal Isolation - Install an isolative fitting, such as a PVC bushing or pipe connection to break the electrical connection of the metallic path.
This information is provided solely as a service to our customers, and in no way infers any liability on the part of Burger & Brown Engineering Inc, Invotec Solutions Limited its representatives, or distributors.
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