Galvanic corrosion, also known as bimetallic corrosion, is a type of electrochemical corrosion that occurs when two different metals are in contact with each other in the presence of an electrolyte, such as saltwater or acidic rain.

In this process, one of the metals, which is more chemically active, undergoes oxidation and loses electrons to the electrolyte, while the other metal, which is less chemically active, undergoes reduction and gains electrons from the electrolyte. This creates an electrochemical cell, with the more active metal acting as the anode and the less active metal acting as the cathode. The anode corrodes and deteriorates over time, while the cathode remains relatively unaffected.

What causes galvanic corrosion?

The following are some of the common causes of galvanic corrosion:

1. Dissimilar metals: When two or more dissimilar metals are in contact with each other, they can create an electrochemical cell that leads to galvanic corrosion.
2. Electrolyte: An electrolyte is a conducting medium that allows the flow of electric current. When two dissimilar metals are in contact with an electrolyte, they can form an electrochemical cell that leads to galvanic corrosion. Examples of electrolytes include saltwater, acid rain, and soil.
3. Temperature: High temperatures can accelerate the rate of galvanic corrosion, especially in the presence of an electrolyte.
4. pH: Galvanic corrosion can occur more rapidly in an acidic environment as compared to a neutral or alkaline environment.
5. Surface area: The larger the surface area of the more active metal, the more likely galvanic corrosion is to occur.
6. Mechanical stress: Mechanical stress can create cracks and fissures in metal surfaces, allowing electrolytes to penetrate and initiate galvanic corrosion.
7. Coating breakdown: When protective coatings break down, they expose the underlying metal to an electrolyte, increasing the risk of galvanic corrosion.
8. Impurities: Impurities in metals can accelerate the rate of galvanic corrosion. For example, impurities in aluminum can cause it to corrode more rapidly when in contact with other metals.

How to recognize galvanic corrosion?

Galvanic corrosion can be recognized through a variety of visual signs and symptoms. Here are some of the most common indicators:

1. Discoloration: When two metals in contact are undergoing galvanic corrosion, one metal may appear darker or lighter in color than the other.
2. Cracking: Galvanic corrosion can cause cracks or fissures in metal surfaces due to the expansion and contraction of the metal.
3. Pitting: Pitting is a type of corrosion that produces small, deep holes in metal surfaces. It can be a sign of galvanic corrosion.
4. Flaking or peeling: Galvanic corrosion can cause the protective coating on a metal surface to flake or peel off, exposing the underlying metal to further corrosion.
5. Swelling or distortion: Galvanic corrosion can cause a metal surface to swell or distort due to the buildup of corrosion products.
6. Staining: The presence of rust stains or discoloration around metal fasteners or fittings can indicate galvanic corrosion.
7. Electrical potential: The electrical potential difference between two metals can be measured using a voltmeter. A high voltage reading between two dissimilar metals may indicate the presence of galvanic corrosion.

Examples of galvanic corrosion

Galvanic corrosion can occur in a wide range of situations, such as when dissimilar metals are in contact in a building structure or when different metals are used in marine environments, such as boats or offshore structures. It can also occur in automobiles, airplanes, and other machinery where different metals are in contact. Here are some examples of galvanic corrosion from daily life;

1. Copper pipes with brass fittings: Copper pipes with brass fittings are commonly used in plumbing systems. However, when these dissimilar metals come in contact with each other and are exposed to water, galvanic corrosion can occur, leading to pipe failure.
2. Aluminum boat with stainless steel fittings: When an aluminum boat comes in contact with stainless steel fittings, such as screws, bolts, or trim tabs, galvanic corrosion can occur due to the dissimilar metals in contact with saltwater.
3. Zinc anode on a boat: Zinc anodes are commonly used on boats to prevent galvanic corrosion. The zinc anode is designed to corrode before other metals, such as aluminum or stainless steel, on the boat, preventing galvanic corrosion.
4. Galvanized steel and copper wire: Galvanized steel and copper wire can be used together in electrical systems. However, when they come in contact with an electrolyte, such as moisture, galvanic corrosion can occur, leading to wire failure.
5. Aluminum gutters with steel nails: When aluminum gutters are attached to a roof with steel nails, galvanic corrosion can occur due to the dissimilar metals in contact with rainwater.
6. Brass lock on a steel door: When a brass lock is attached to a steel door, galvanic corrosion can occur due to the dissimilar metals in contact with humidity and temperature changes.
7. Steel structure with stainless steel bolts: When a steel structure is assembled using stainless steel bolts, galvanic corrosion can occur due to the dissimilar metals in contact with rainwater and other environmental factors.
8. Steel car body with aluminum wheels: When steel car bodies come in contact with aluminum wheels, galvanic corrosion can occur due to the dissimilar metals in contact with moisture, road salt, and other environmental factors.
9. Zinc-coated steel fence with copper wiring: When zinc-coated steel fences come in contact with copper wiring, galvanic corrosion can occur due to the dissimilar metals in contact with rainwater and soil moisture.
10. Copper water pipes with iron or steel fittings: When copper water pipes come in contact with iron or steel fittings, galvanic corrosion can occur due to the dissimilar metals in contact with water and other chemicals in the plumbing system.
11. Stainless steel grill with aluminum foil: When aluminum foil is used to wrap food on a stainless steel grill, galvanic corrosion can occur due to the dissimilar metals in contact with heat, moisture, and other chemicals.
12. Steel reinforcing bars in concrete with stainless steel fasteners: When steel reinforcing bars in concrete structures come in contact with stainless steel fasteners, galvanic corrosion can occur due to the dissimilar metals in contact with moisture and other chemicals in the concrete.
13. Copper roof with zinc gutters: When copper roofs are connected to zinc gutters, galvanic corrosion can occur due to the dissimilar metals in contact with rainwater and other environmental factors.
14. Brass keys with steel keyholes: When brass keys are inserted into steel keyholes, galvanic corrosion can occur due to the dissimilar metals in contact with humidity, temperature changes, and other environmental factors.

How to prevent galvanic corrosion?

1. Avoid using dissimilar metals in contact with each other: When selecting materials for a project, it’s important to choose metals that are compatible with each other. Avoid using dissimilar metals, such as aluminum and copper, in contact with each other.
2. Use non-conductive materials: Using non-conductive materials, such as rubber or plastic, between dissimilar metals can help prevent galvanic corrosion.
3. Apply protective coatings: Applying protective coatings, such as paint, lacquer, or epoxy, to metal surfaces can help prevent galvanic corrosion by creating a barrier between the metal and the environment.
4. Use sacrificial anodes: Sacrificial anodes, such as zinc or aluminum, can be installed on boats or other structures to protect against galvanic corrosion. The sacrificial anode corrodes instead of the metal it is protecting.
5. Use isolation flanges: Isolation flanges can be used in piping systems to prevent galvanic corrosion. The flanges isolate the dissimilar metals from each other.
6. Monitor electrical potential: Measuring the electrical potential difference between dissimilar metals can help identify potential galvanic corrosion problems before they become serious.
7. Keep surfaces clean and dry: Keeping metal surfaces clean and dry can help prevent galvanic corrosion by reducing the amount of moisture and other chemicals in contact with the metal.