Corrosion

Degradation of materials due to chemical reactions

For the band, see Corrosion of Conformity.

A bolt showing signs of rust, a common form of corrosion.

Corrosion on riveted joints.

Galvanic corrosion of aluminum and steel in seawater.

Gold is highly resistant to corrosion.

Corrosion is the gradual destruction of materials, usually metals, by chemical and/or electrochemical reaction with their environment. It is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide. Corrosion can lead to the deterioration of properties of the material, which can compromise the integrity and functionality of structures and components.

Types of Corrosion

Corrosion can occur in various forms, each with distinct characteristics and mechanisms:

Uniform Corrosion

Uniform corrosion, also known as general corrosion, occurs evenly across the surface of a material. It is the most common form of corrosion and is typically predictable and manageable.

Galvanic Corrosion

Galvanic corrosion occurs when two different metals are in electrical contact in the presence of an electrolyte. The more active metal (anode) corrodes faster than it would alone, while the less active metal (cathode) corrodes slower.

Pitting Corrosion

Pitting corrosion is a localized form of corrosion that leads to the creation of small holes or pits in the material. It is often more dangerous than uniform corrosion because it is harder to detect and can lead to structural failure.

Crevice Corrosion

Crevice corrosion occurs in confined spaces where the access of the working fluid from the environment is limited. It is often found in joints, gaskets, and under deposits.

Intergranular Corrosion

Intergranular corrosion occurs along the grain boundaries of a metal. It is often associated with improper heat treatment and can lead to significant weakening of the material.

Stress Corrosion Cracking (SCC)

SCC is the growth of crack formation in a corrosive environment. It can lead to sudden and catastrophic failure of a material under tensile stress.

Prevention and Control

Several methods are employed to prevent or control corrosion:

• Material Selection: Choosing materials that are inherently resistant to corrosion, such as stainless steel or non-metallic materials.
• Protective Coatings: Applying paints, plating, or other coatings to protect the material from the environment.
• Cathodic Protection: Using sacrificial anodes or impressed current systems to protect the metal from corrosion.
• Corrosion Inhibitors: Adding chemicals to the environment that decrease the rate of corrosion.
• Design Modifications: Designing structures to avoid crevices, ensure proper drainage, and minimize galvanic coupling.

Applications and Implications

Corrosion has significant economic and safety implications. It affects a wide range of industries, including construction, transportation, and energy. The cost of corrosion is estimated to be billions of dollars annually, considering both direct costs (maintenance, repair, and replacement) and indirect costs (downtime, loss of efficiency, and safety hazards).

Also see

• Rust
• Electrochemistry
• Metal fatigue
• Passivation
• Oxidation