Corrosion is a natural process that converts a refined metal to a more chemically-stable form such as oxides, hydroxides, or sulfides. It is the gradual destruction of materials through chemical reaction with their environment. Left unprotected, corrosion can compromise the integrity and structural longevity of assets like buildings, bridges, ships, pipelines, and more. Preventing corrosion is therefore critical, especially for infrastructure and structures integral to industry, transportation, and public safety.
Causes of Corrosion
There are several factors that can contribute to corrosion:
Moisture: The presence of water or humidity is necessary for many corrosion reactions to occur. Water allows ions and molecules to contact metal surfaces.
Oxygen: Most metallic corrosion involves oxidation reactions that require oxygen from air to proceed. Areas with little air circulation are more prone to corrosion.
Chemicals: Certain acids, alkalis, salts, and other chemicals are aggressive electrolytes that accelerate corrosion by increasing the conductivity of the corrosive solution. Common examples include sulfur and chlorine compounds.
Temperature: Higher temperatures increase the rate of most corrosion reactions by providing energy to break bonds. However, some materials may suffer stress corrosion cracking at lower temperatures.
Stress: Mechanical or residual stresses concentrate strains and make metals more susceptible to localized corrosion damage like pitting or crack growth. Welds are highly stressed.
Microbiology: Corrosion Protective Coatings Certain microbes actually aid corrosion by producing or changing the local chemistry. Sewage, soils and some internal metal surfaces are vulnerable to microbiologically influenced corrosion.
Galvanic corrosion: Dissimilar metals in electrical contact will corrode the more active metal preferentially due to electrical potential differences in the galvanic series. Seawater is a particularly corrosive medium.
Importance of Corrosion Protective Coatings
Applying protective coatings to metal structures is a highly effective way to impede corrosion. Coatings work in several ways:
- They act as a physical barrier that separates the metal substrate from its corrosive environment, preventing destructive ions and molecules from making contact. Even micron-thin barriers significantly retard corrosion rates.
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