Corrosion: Types, Prevention, and Effects

Corrosion

Introduction

Corrosion is the natural degradation mechanism of materials, particularly metals, when exposed to environmental factors such as atmospheric agents, pollutants, or other physical conditions. It is an electrochemical process involving the transfer of electrons and ions between the material's surface and its surroundings. Corrosion can lead to structural deterioration, performance decline, and safety risks in various applications, including infrastructure, transportation, energy, and construction industries.

Types of Corrosion

Uniform (Generalized) Corrosion

This type of corrosion is the most common and appears over the entire surface of a metal, causing a uniform decrease in thickness. It affects all materials equally and can be detected early due to its visible nature. Uniform corrosion is mainly triggered by external factors like thermal gradients or aggressive media composition and is relatively easy to eliminate once identified and treated.

Localized Corrosion

Localized corrosion is focused on specific areas of a material, often resulting in pits or crevices. It is more challenging to detect and can lead to severe degradation. The most common types of localized corrosion are:

• Pitting Corrosion: Formed by localized failures in a coating system, with small holes developing at points of failure and expanding if left untreated.
• Crevice Corrosion: Occurs in micro-spaces between touching materials, such as metal-on-metal or metal-against-non-metal points of contact, and is often found near bolts, gaskets, washers, or other fasteners.
• Filiform Corrosion: Resulting from moisture infiltration into the narrow space between a coating and the substrate, usually observed at natural edges on the substrate or defects in the coating system.
• Pack Rust: Generated when steel components create an exposed crevice, typically in bridge structures where rust builds up between two meeting surfaces.
• Galvanic Corrosion: Induced by different materials in electrical contact under water, causing rapid deterioration of the surface metal.
• Lamellar Corrosion: Characterized by layers in the metal, progressing along planes parallel to the surface and occurring predominantly in extruded aluminum alloys.

Prevention of Corrosion

Effective corrosion prevention requires considering environmental factors and employing suitable preventative measures. Corrosion-resistant coatings are among the most reliable and cost-effective options for most forms of corrosion. Common prevention strategies include:

• Electroplating: Deposition of a thin layer of another metal onto the surface of the metal to improve its corrosion resistance.
• Galvanization: Application of a layer of zinc to the surface of steel to protect it from corrosion.
• Anodization: Treatment of aluminum to produce a durable oxide layer that enhances its corrosion resistance.
• Passivation: Process of making a metal passive to inhibit active corrosion, typically performed on stainless steel.
• Biofilm Coatings: Utilize living organisms or their byproducts to form a protective layer on the metal surface.
• Anti-Corrosion Protective Coatings: Provide a barrier against corrosive elements, such as oxygen and moisture.
• Painting and Greasing: Applying paint or grease to protect the metal from moisture and contaminants.
• Use of Corrosion Inhibitors or Drying Agents: Application of chemicals that retard or halt corrosion.
• Periodic Cleaning of Metal Surfaces: Removing dirt, debris, and impurities that promote corrosion.

Effects of Corrosion on Materials

The consequences of corrosion can range from mild degradation to catastrophic failures. High levels of corrosion can lead to:

• Waste of natural resources and raw materials.
• Weak and unstable building structures.
• Dangerous situations such as transportation accidents caused by corroded parts.
• Cracked pipelines.
• Collapsing bridges.

Understanding the causes, types, and prevention strategies for corrosion is crucial for selecting appropriate protection techniques and maintaining the integrity of critical infrastructure and equipment.