Corrosion
Corrosion is a natural process that converts refined metal to a more chemically stable form such as oxides, hydroxides, or sulfides. It is the gradual destruction of materials (usually metals) by chemical and electrochemical reaction with their environment. Unprotected steel will generally corrode at a rate of over 25 micrometers (1 mil or 0.001 inch) per year when exposed to normal weathering. Corrosion not only damages the aesthetic appearance of materials and structures but can also compromise their strength, stability and functionality over time.
Causes of Corrosion
There are few major causes for corrosion in metals including water, oxygen, chemicals, abrasion and temperature variations. Exposure to water causes rusting of iron-based metals like steel. Oxygen in the air or water reacts with metals to form metal oxides. Salt in the air or water promotes corrosion by drawing out moisture. Industrial chemicals can be very corrosive depending on their pH and composition. Friction or wear and tear leads to abrasive corrosion. Changes in temperature cause expansion and contraction which weakens protective surface layers and promotes corrosion.
Types of Corrosion
The main types of Anti-Corrosion Coatings seen in metals include rusting, galvanic corrosion, pitting corrosion, stress corrosion cracking and crevice corrosion. Rust is the most common type seen in iron and steel exposed to moisture and oxygen. Galvanic corrosion occurs due to dissimilar metal contact in the presence of an electrolyte. Pitting corrosion causes formation of isolated cavities or pockets on the metal surface. Stress corrosion cracking is influenced by both mechanical stress and a corrosive substance. Crevice corrosion affects regions shielded from full exposure such as joints, welds or under gasket materials.
Working of Anti Corrosion Coatings
Anti-corrosion coatings work as a barrier between the corrosive environment and the metal surface they protect. They inhibit corrosion by preventing corrosive agents like water, oxygen, industrial chemicals from coming in contact with the metal. The coatings can be applied as liquid, powder or film and through spraying, brushing, dipping or other methods. Once cured, they create an impervious layer over the metal that is resistant to chemicals, thermal and weathering effects. Some coatings have corrosion inhibitors added which migrate to failures in the coating layer and stop corrosion progression. Multiple coats may be required to achieve complete barrier protection. Properly applied coatings can last for 10-30 years depending on environmental conditions and surface preparation.
Types
There are several anti-corrosion coatings technologies used for corrosion protection of metals in different industries and applications:
1. Paint Coatings - Conventional oil and alkyd-based paints as well as advanced polyurethane, epoxy and acrylic coating systems. They are widely used for steel structures, pipes, equipment and vehicles.
2. Powder Coatings - Made of thermoplastic or thermoset polymer powders that melt and cure on substrate surface. Provide excellent adhesion, hardness and longevity. Used for architectural, industrial and electronic applications.
3. Galvanizing - A zinc coating applied by hot-dip galvanizing or electroplating which provides cathodic protection. Highly effective on steel sheets, pipes, hardware etc.
4. Thermal Spray Coatings - Made by spraying melted or heated materials via flame, combustion or plasma guns to form thick coatings. Examples are metallic zinc, aluminum, titania used for oil rigs, ships etc.
5. Lining Systems - Cementitious and polymeric materials supplied as slurry or trowelable formula applied as linings in storage tanks, pipelines etc. Provide corrosion protection from inside.
6. Tape Coatings - Protective tapes made of polymers impregnated with corrosion inhibitors. Used as temporary coatings or over undercoated areas for additional resistance.
Performance and Maintenance
Properly selected and applied anti-corrosion coatings having appropriate film properties can deliver long-term corrosion protection for metals even under severe environmental conditions. However, damaged coatings from scratches, impacts or dissimilar metal contact need timely maintenance through spot repair, recoating or cathodic protection. Periodic coating condition monitoring also allows corrective action before major corrosion sets in thus saving on long-term costs and downtime. With proper surface preparation and maintenance, modern corrosion control coatings can significantly extend the service life of metals assets.
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Money Singh is a seasoned content writer with over four years of experience in the market research sector. Her expertise spans various industries, including food and beverages, biotechnology, chemical and materials, defense and aerospace, consumer goods, etc. (https://www.linkedin.com/in/money-singh-590844163)