What is Corrosion?
Corrosion refers to the chemical or electrochemical reaction of materials, especially metals, with environmental factors (such as water, oxygen, acids, alkalis, salts, etc.), leading to the degradation or damage of the material’s surface or internal structure.
The most common form of corrosion is oxidation, such as rusting of iron, where iron reacts with oxygen to form iron oxide.
Corrosion significantly reduces the strength and durability of materials, leading to equipment failure, increased maintenance and replacement costs, reduced production efficiency, and safety risks. Additionally, corrosion can cause leaks, explosions, and other safety incidents, resulting in environmental pollution and shorter equipment lifespans, thereby incurring high economic losses.
Corrosion not only affects the performance and appearance of equipment but can also pose serious risks to personnel safety, the environment, and the long-term development of businesses.
Corrosion can be classified into various types based on its formation mechanism, environmental conditions, and impact on materials. Common types of corrosion include:
Uniform Corrosion
The most common form of corrosion, it occurs uniformly across the metal surface, gradually reducing the thickness of the metal. It typically occurs in environments exposed to corrosive media such as acids, alkalis, or water.
Prevention: Use corrosion-resistant materials (e.g., stainless steel, aluminum alloys), perform regular cleaning and maintenance, and avoid prolonged exposure to corrosive media.
Surface Treatment: Apply protective coatings or use cathodic protection.
Localized Corrosion
Corrosion concentrates in specific areas on the metal surface, forming pits, cracks, or grooves. Examples include:
Pitting Corrosion:
Corrosion forms small holes or pits, commonly occurring in corrosive media like chlorides.
Crevice Corrosion:
Occurs in areas with small gaps on the metal surface, such as joints and bolt holes.
Groove Corrosion:
Typically occurs in areas with uneven liquid flow, forming localized corrosion zones.
Prevention: Avoid cracks or gaps on the metal surface and perform regular inspections and cleaning.
Pitting Prevention: Use alloys with high resistance to pitting, such as high-alloy stainless steel; apply coatings or external protection.
Crevice Corrosion Prevention: Maintain good joint design and avoid moisture or water accumulation in crevices.
Stress Corrosion Cracking (SCC)
Corrosion and external or internal stress act together, causing cracks in metals. It is common in high-strength steels and stainless steels, especially in corrosive environments like chlorides.
Prevention: Avoid stress concentrations, particularly in high-strength steels and stainless steels. Use appropriate materials (e.g., low-carbon stainless steel) and control the corrosive nature of the environment.
Reduce Stress: Prevent excessive external or internal stresses and perform regular inspections and maintenance.
Hydrogen Embrittlement
Hydrogen atoms infiltrate the metal, making it brittle and prone to fracture, commonly occurring in high-strength steels and nickel-based alloys.
Prevention: Avoid prolonged exposure to hydrogen environments, particularly in high-strength steels. Use hydrogen-resistant materials, such as low-hydrogen alloys.
Heat Treatment: Perform heat treatment (dehydrogenation) after processing to reduce hydrogen accumulation.
Sulfide Stress Cracking (SSC)
Mainly occurs in the oil and gas industry when metals are exposed to sulfides (such as H₂S). Stress and corrosion together cause cracks.
Prevention: Use alloys resistant to sulfide corrosion, particularly in H₂S environments.
Protective Coatings: Apply sulfur-resistant coatings or protective materials.
Occurs when two different metals come into contact and are exposed to an electrolyte solution, where one metal corrodes as the anode and the other acts as the cathode. The corrosion rate is faster between metals with a significant electrochemical potential difference.
Prevention: Avoid direct contact between different metals or isolate them using electrical insulating materials.
Use Similar Metals: Ensure that metals connected have similar electrochemical potentials to reduce the corrosion rate.
Microbial Corrosion / Biocorrosion
Corrosion caused by microorganisms (e.g., bacteria, fungi), common in humid or low-oxygen environments, such as marine pipelines and storage tanks.
Prevention: Control the growth environment of microorganisms, such as keeping pipelines and tanks clean and dry, and use antimicrobial coatings.
Chemical Treatment: Regularly use antimicrobial agents or disinfectants to prevent microorganism growth.
High Temperature Corrosion
Occurs in high-temperature environments, especially when metals are exposed to corrosive gases such as oxygen, sulfides, or chlorides, leading to oxidation or sulfation.
Prevention: Use high-temperature-resistant alloys, such as Inconel or Hastelloy, and avoid excessive temperatures and exposure to corrosive gases.
Coating Protection: Apply high-temperature corrosion-resistant coatings or metallic spray treatments.
Oxidation Corrosion
Oxidation Corrosion Occurs when metals react with oxygen, forming oxides. It is common in metals like iron and aluminum. Iron oxidation forms rust, while stainless steel and aluminum alloys form protective oxide layers.
Prevention: Use anti-oxidation coatings or passivation treatments (forming protective oxide films on metal surfaces).
Material Selection: Choose materials with high resistance to oxidation, such as aluminum or chromium.
Dry-Wet Corrosion
Dry-Wet Corrosion occurs in environments with moisture, where metals exposed to oxygen and water or steam corrode.
Prevention: Avoid exposing metals to humid or wet environments, and use corrosion-resistant coatings or paints to isolate water.
Ventilation and Drying: Improve working environments by maintaining dryness, especially in humid marine or underground environments.
In conclusion
Each type of corrosion has its specific mechanism and environmental conditions, so corrosion prevention measures must be tailored accordingly in industrial applications. In general, the key to preventing corrosion is to select appropriate materials, perform regular maintenance and inspections, and adopt effective protective measures such as coatings, cathodic protection, and appropriate heat treatments.
