Corrosion inhibitors

Types of Corrosion Inhibitors

• Anodic Inhibitors

  • Mechanism: Form a protective oxide layer on the metal surface, reducing anodic reaction rates.
  • Examples: Sodium molybdate, Sodium nitrate.
  • Applications: Effective for systems with moderate to high corrosion potential.

• Cathodic Inhibitors

  • Mechanism: Slow down the cathodic reaction, usually by precipitating a compound on the cathodic areas.
  • Examples: Zinc salts, Polyphosphates.
  • Applications: Often used in combination with anodic inhibitors for comprehensive protection.

• Mixed Inhibitors

  • Mechanism: Provide both anodic and cathodic protection.
  • Examples: Orthophosphates, Phosphonates, Silicates.
  • Applications: Widely used due to their broad-spectrum protection.

• Organic Inhibitors

  • Mechanism: Adsorb onto metal surfaces to form a protective hydrophobic film.
  • Examples: Filming amines, Benzotriazole.
  • Applications: Effective in protecting against both general and localized corrosion.

• Passivating Inhibitors

  • Mechanism: Promote the formation of a passive oxide layer on metal surfaces.
  • Examples: Chromates (less common due to environmental concerns), Nitrites.
  • Applications: Used where a strong and stable passive layer is required.

Factors to Consider When Choosing Corrosion Inhibitors

• Water Chemistry: The chemical composition of the cooling water, including pH, alkalinity, hardness, and the presence of corrosive ions (e.g., chloride, sulfate), influences the choice of inhibitors.
• System Materials: The materials of construction for the cooling tower and associated equipment (e.g., carbon steel, stainless steel, copper) should be compatible with the chosen inhibitor.
• Operating Conditions: Temperature, flow rates, and other operating conditions can affect the performance of corrosion inhibitors.
• Compatibility with Other Chemicals: Ensure the chosen inhibitors are compatible with other treatment chemicals used in the system (e.g., biocides, scale inhibitors).
• Environmental and Safety Considerations: Select inhibitors that comply with environmental regulations and safety standards.

Benefits of Using Corrosion Inhibitors

• Protection of Metal Surfaces: Inhibitors prevent or reduce the rate of corrosion, extending the lifespan of cooling tower components.
• Improved System Efficiency: By preventing corrosion, inhibitors help maintain optimal heat transfer efficiency.
• Reduced Maintenance Costs: Minimizing corrosion reduces the need for repairs and replacements, lowering maintenance costs.
• Enhanced Water Use: Inhibitors can allow for higher cycles of concentration, reducing the need for fresh water and lowering wastewater discharge.

Application Methods

• Continuous Dosing: Corrosion inhibitors are continuously added to the cooling water to ensure consistent protection.
• Batch Dosing: In some systems, inhibitors are added in batches based on water usage and operating conditions.
• Automated Dosing Systems: Advanced systems use sensors and automated controls to monitor water chemistry and adjust inhibitor dosing in real time.