Short Answer:

Galvanic corrosion happens when two different metals come into contact with each other in the presence of an electrolyte, like water or moisture. One of the metals becomes the anode and corrodes faster, while the other becomes the cathode and remains protected. The less noble (more active) metal loses electrons and gets damaged over time.

To prevent galvanic corrosion, engineers use techniques like insulating the metals from each other, applying protective coatings, using similar metals, or adding a sacrificial anode. These methods stop the flow of electrons between metals, reduce corrosion risk, and increase the life of the structure or component.

Detailed Explanation:

Galvanic corrosion and its prevention

Galvanic corrosion, also called bimetallic corrosion, is a common problem in mechanical, marine, and construction applications. It occurs when two dissimilar metals are connected in a wet or moist environment. This situation creates a type of battery, where one metal corrodes to protect the other.

Understanding how galvanic corrosion works and how to prevent it is very important for building long-lasting machines, pipes, tanks, and structures where different metals are often used together.

How galvanic corrosion occurs

Galvanic corrosion happens when three conditions are present:

1. Two different metals (like steel and copper) are connected.
2. Electrical contact is made between them (physically touching).
3. Electrolyte is present, usually water or moisture that allows ions to move.

When this setup occurs:

• One metal acts as the anode (more active), and the other as the cathode (more noble or less reactive).
• The anode loses electrons and corrodes.
• The cathode gains electrons and remains protected.

This flow of electrons from the anode to the cathode through the electrical connection and ions through the electrolyte causes the anode metal to break down over time.

Example of galvanic corrosion

• Connecting aluminum and copper pipes in a plumbing system can cause galvanic corrosion of aluminum.
• Using steel bolts on a copper roof can lead to steel corrosion.

In both examples, moisture in the air or water acts as the electrolyte.

Factors that increase galvanic corrosion

• Larger difference in metal activity: The greater the gap in the galvanic series, the faster the anode corrodes.
• Large cathode and small anode: A small anode has to supply more electrons, so it corrodes faster.
• Presence of salt or acidic water: These make the electrolyte stronger and speed up corrosion.
• Poor ventilation: Trapped moisture between metals increases corrosion chances.

How to prevent galvanic corrosion

1. Use similar metals
   • Choose metals close to each other in the galvanic series.
   • This reduces the potential difference and slows down corrosion.
2. Apply protective coatings
   • Use paint, varnish, or powder coating to isolate the metals from moisture.
   • Coat both metals or at least the more noble one (cathode).
3. Use electrical insulation
   • Place rubber washers, plastic spacers, or non-conductive sleeves between metals.
   • This stops electron flow between them.
4. Use sacrificial anodes
   • Attach a more reactive metal (like zinc) that corrodes instead of the important metal.
   • Common in marine applications, pipelines, and storage tanks.
5. Control the environment
   • Keep the area dry and clean.
   • Avoid using dissimilar metals in damp or corrosive environments.
6. Design for maintenance
   • Allow easy access to joints and connections for inspection and replacement.
   • Avoid sharp edges and tight crevices where moisture can collect.

Applications where prevention is critical

• Ship hulls and marine equipment
• Bridges and outdoor structures
• HVAC systems with mixed metal components
• Oil pipelines and water tanks
• Buildings with metal roofs, railings, and fasteners made of different metals

Ignoring galvanic corrosion can lead to early failure, leakage, or collapse of structures and machines.

Conclusion

Galvanic corrosion is a common but preventable form of corrosion that occurs when two different metals are connected in a moist environment. One metal corrodes while the other stays safe. By using smart design, protective coatings, electrical insulation, or sacrificial anodes, engineers can prevent or reduce this damage. Understanding how galvanic corrosion occurs and how to control it is essential for creating strong, durable, and long-lasting structures and mechanical systems.