Galvanic Corrosion Occurrence and Prevention
Galvanic Corrosion Occurrences and Prevention refers to the process of preventing metal or alloy affected by corrosion.
Galvanic Corrosion is an electrochemical process which refers to corrosion damage occurs when two dissimilar materials are integrated into a corrosive electrolyte. Galvanic Corrosion occurs when a metal or alloy is electrically coupled to a different metal or alloy. Dissimilar metals and alloys have different electrode potentials. When a galvanic couple form or more than one metals come into contact with an electrolyte, one metal acts as an anode and the other as a cathode.
The pair of the anode (Negative terminals) and cathode (Positive terminals) creates a galvanic cell.
Identifying Galvanic Corrosion:
- Scratches in a metal surface
- A leak on an aluminum-hulled vessels
- Blistered or peeling paintwork
- Corrosion occurs in corrugated iron
- Differential stresses in a metal
- Difference in temperature
- Conductive deposits
Galvanic Corrosion generally occurred on Al-Cu Metal Bond pad corrosion during water saw resulting in pitting.
Main factors influencing galvanic corrosion rates:
The potential difference between materials.
Cathode efficiency and the potential difference
The Ratio of the cathodic and anodic region and Deposition of Impurities
An electrical resistance of the connection between the materials and of the electrolyte
pH of the medium, Temperature, and Effect of oxygen.
Presence of passive film.
Surface Area Effects in a Galvanic Corrosion Situation:
Area effects or the ration of cathodic to an anodic area is one of the important factor influencing galvanic corrosion. The more oxygen reduction or the cathodic reaction can occur due to larger the cathode compared with the anode resulting greater the galvanic current. The galvanic table indicated that iron is anodic (Positive terminal) with respect to copper and therefore when placed in contact with it, it is more quickly corroded.
Galvanic Corrosion Prevention for Metal:
Different metals have different electrochemical potentials in the common electrolyte. When two dissimilar metals come into electrical contact and both metals are immersed in an electrolyte such as water, then Galvanic Corrosion occurs. Typically in an HVAC System (Heating, Ventilation, and Conditioning) in an industry, various metals of construction will be used, they are connected via Flange, valve, union, or brazed joint. Metallic coatings are applied to provide corrosion protection to steels.
Galvanic Series: Galvanic Series is a list of measured corrosion potentials to determine the nobility of a number of metals and alloys in a given electrolyte. This is done by illustrating which material has a minimal tendency to a galvanic interaction.
There are several ways of reducing Galvanic Corrosion:
- Galvanic Corrosion also is known as bi-metallic corrosion is a process which occurs due to electric contacts of dissimilar metal in the presence of an electrolyte. To prevent your metal from corrosion select metals/alloys as close together as possible in the galvanic series.
- Prevent galvanic corrosion by coating the metal which can isolate the metals from the environment (Zinc flake/Aluminium rich coating system).
- Design for small Ac/Aa area ratio
- Give thickness allowance for the more active metal.
- Coat the cathode to reduce Ac/Aa.
- During designing the components, use replacement part so that it is easy to replace only affected or corroded parts instead of the whole machine parts.
- Insulate dissimilar metals wherever needed practical.