Galvanic Corrosion vs. Stress Corrosion

Attribute	Galvanic Corrosion	Stress Corrosion
Definition	Corrosion caused by the electrochemical interaction between two dissimilar metals in the presence of an electrolyte.	Corrosion that occurs due to the combined effect of tensile stress and a corrosive environment.
Mechanism	Electrochemical reaction between dissimilar metals.	Chemical reaction influenced by tensile stress.
Causes	Presence of dissimilar metals and an electrolyte.	Tensile stress and a corrosive environment.
Electrolyte	Presence of an electrolyte is necessary for the electrochemical reaction to occur.	An electrolyte is not required for stress corrosion to take place.
Metals Involved	Occurs between dissimilar metals in contact with each other.	Can occur in a single metal or between dissimilar metals.
Effect on Material	Localized corrosion at the interface of dissimilar metals.	Cracking or failure of the material due to the combined effect of stress and corrosion.
Prevention	Use of protective coatings, sacrificial anodes, or isolation of dissimilar metals.	Control of stress levels, use of corrosion-resistant materials, or modification of the environment.

Introduction

Corrosion is a natural process that occurs when metals react with their environment, leading to the deterioration of their properties. It is a significant concern in various industries, including construction, manufacturing, and transportation. Two common types of corrosion that can cause significant damage to metal structures are galvanic corrosion and stress corrosion. While both types involve the degradation of metals, they differ in their mechanisms, causes, and prevention methods. This article aims to compare the attributes of galvanic corrosion and stress corrosion, shedding light on their distinct characteristics.

Galvanic Corrosion

Galvanic corrosion, also known as bimetallic corrosion, occurs when two dissimilar metals come into contact in the presence of an electrolyte, such as moisture or saltwater. This contact creates a galvanic cell, where one metal acts as an anode and the other as a cathode. The anode undergoes oxidation, releasing electrons, while the cathode undergoes reduction, accepting the electrons. This electron flow leads to the corrosion of the anode, causing it to deteriorate over time.

One of the key factors that contribute to galvanic corrosion is the difference in electrode potential between the two metals. This potential difference, also known as the galvanic series, determines the likelihood of corrosion. When two metals with a significant potential difference are in contact, the corrosion rate increases. For example, when aluminum and steel are in contact, the aluminum acts as the anode and corrodes more rapidly than it would in isolation.

Preventing galvanic corrosion involves isolating the dissimilar metals or introducing a sacrificial anode. Isolation can be achieved by using non-conductive materials, such as rubber or plastic, to separate the metals. Alternatively, a sacrificial anode made of a more reactive metal can be connected to the structure, diverting the corrosion to the sacrificial metal instead. Regular maintenance and protective coatings can also help minimize the risk of galvanic corrosion.

Stress Corrosion

Stress corrosion, also known as stress corrosion cracking (SCC), is a specific type of corrosion that occurs when a metal is exposed to a corrosive environment while under tensile stress. Unlike galvanic corrosion, stress corrosion does not require the presence of dissimilar metals. It can affect a single metal or alloy, making it a more complex phenomenon to understand and prevent.

The combination of tensile stress and a corrosive environment leads to the initiation and propagation of cracks in the metal. These cracks can grow rapidly and cause catastrophic failure, even in materials that would normally be resistant to corrosion. Stress corrosion is often influenced by factors such as temperature, humidity, and the specific alloy composition of the metal.

Preventing stress corrosion involves reducing or eliminating the tensile stress on the metal and controlling the environment in which it is exposed. Stress relief techniques, such as heat treatment or mechanical relaxation, can help reduce the residual stress in the metal. Additionally, selecting corrosion-resistant alloys and implementing proper design practices can minimize the risk of stress corrosion.

Comparison

While both galvanic corrosion and stress corrosion involve the degradation of metals, they differ in several key aspects:

• Mechanism: Galvanic corrosion occurs due to the electrochemical reaction between dissimilar metals, while stress corrosion is a result of the combined effects of tensile stress and a corrosive environment.
• Causes: Galvanic corrosion is primarily caused by the contact between dissimilar metals, whereas stress corrosion is influenced by factors such as tensile stress, temperature, humidity, and alloy composition.
• Types of metals affected: Galvanic corrosion affects dissimilar metals in contact, while stress corrosion can affect a single metal or alloy.
• Prevention methods: Galvanic corrosion can be prevented by isolating the dissimilar metals or using sacrificial anodes, while stress corrosion prevention involves reducing tensile stress and controlling the corrosive environment.
• Risk factors: Galvanic corrosion is more likely to occur when metals with a significant potential difference are in contact, while stress corrosion is influenced by factors such as the level of tensile stress and the specific environment.

Conclusion

Galvanic corrosion and stress corrosion are two distinct types of corrosion that can cause significant damage to metal structures. Galvanic corrosion occurs when dissimilar metals come into contact, while stress corrosion is a result of the combined effects of tensile stress and a corrosive environment. Understanding the mechanisms, causes, and prevention methods for each type of corrosion is crucial for industries that rely on metal structures. By implementing appropriate preventive measures, such as isolating dissimilar metals or reducing tensile stress, the risk of corrosion-related failures can be minimized, ensuring the longevity and safety of metal components.