Industrial cooling systems, particularly cooling towers and associated condensation trains, are complex hydrodynamic environments where electrochemical corrosion, biofouling, and mineral deposition phenomena converge. The interaction between pH variations, dissolved gases, ionic loads, and microbiological activity generates highly aggressive conditions for ferrous and non-ferrous alloys, compromising mechanical integrity and thermal efficiency.
Dominant electrochemical mechanisms in industrial cooling systems
In recirculating cooling circuits, corrosion is dominated by electrochemical processes activated by high conductivities, thermal gradients, acidity, and the presence of dissolved gases. The lack of stability in passive films and the formation of galvanic cells induced by aeration differences increase susceptibility to accelerated thickness loss and erosion-corrosion phenomena, affecting pipes, exchangers, and metal components exposed to turbulence and cavitation.
Electrochemical mechanisms in recirculated water
Corrosion in cooling circuits is caused by the alteration of the electrochemical balance of the metal in the presence of water with high ionic conductivity, dissolved gases, and thermal gradients.
- Acidity (pH < 7.5) promotes the cathodic reaction of hydrogen reduction and accelerates the anodic dissolution of iron.
- Mineral acids (H₂SO₄, HCl) cause generalized, accelerated corrosion and localized depassivation.
- Dissolved CO₂: forms carbonic acid H₂CO₃, reducing the pH and intensifying overall corrosion.
- Dissolved oxygen (O₂): promotes corrosion through differential aeration, especially in turbulent areas and splash zones.
Associated effects:
- Decrease in metallurgical thickness.
- Cavitation and erosion-corrosion at points of hydraulic impact.
- Decrease in overall heat transfer coefficient.
Biofouling and microbiological corrosion
The colonization of metal surfaces by microorganisms generates biofilms with electrochemical gradients that modify the anodic and cathodic kinetics of the exposed metal. Partial oxygen inhibition, the production of organic acids and hydrogen sulfide, and the formation of anaerobic microenvironments promote localized deep corrosion (MIC), increasing the rate of metal penetration and the risk of premature perforations.
Biological colonization and microbial degradation
The presence of microorganisms alters corrosion kinetics through biofilm formation, oxygen consumption, and the generation of corrosive byproducts.
| Agent | Technical effect |
| Seaweed | O₂ release → oxidative corrosion; surface clogging |
| Slime-forming bacteria | MIC due to local acidification and galvanic cells |
| Fungi | Deterioration of organic structures (wood) and moisture retention |
Biological buildup generates aerobic/anaerobic cells, increasing localized corrosion, pitting, and deep metal penetration.
Mineral deposits and mass transport
The progressive concentration of salts through evaporation cycles promotes the precipitation of carbonates, sulfates, and silicates, causing layers of incrustation to form. These deposits act as thermal barriers and create environments with differential oxygen levels that induce under-deposit corrosion (UDC), promoting local acidification, the formation of galvanic cells, and a significant loss of thermal efficiency.
Fouling and its effect on induced corrosion
Recurrent evaporation increases the concentration of salts, promoting the scaling of carbonates, sulfates, and silicates on metal surfaces. These deposits create differential oxygenation zones that induce under-deposit corrosion (UDC):
- Local anodic acceleration.
- Microenvironmental pH gradients.
- Loss of thermal efficiency and increase in ΔT.
Degradation modes by system type
Degradation mechanisms vary depending on the cooling system architecture, operating conditions, hydraulic regime, and water chemistry. Closed systems tend to suffer from chemical and galvanic corrosion, while open systems are more susceptible to MIC, fouling, and corrosion induced by differential aeration, especially in areas of contact with the atmosphere and extreme turbulence. The following table shows the most common failures.
Failure patterns according to operating configuration
| System | Predominant mechanism | Consequence |
| Industrial HVAC | Atmospheric deposits | Dirting and heat loss |
| Chillers | Acid and galvanic corrosion | Pipeline leaks and deterioration |
| Cooling towers | MIC + incrustation + CO₂ | Differential cells and critical stoppages |
Advanced mitigation strategies
Comprehensive corrosion control requires a combination of chemical water management, electrochemical inhibition, microbiological disinfection, and advanced online monitoring technologies. Robust programs integrate synergistic inhibitors, alternating biocides, controlled purges, and electrochemical sensors, enabling predictive management based on data and aligned with integrity engineering.
Comprehensive treatment and monitoring programs
| Control | Function |
| pH and alkalinity control | Chemical stabilization of water |
| Mixed inhibitors | Control of anodic and cathodic reactions |
| Alternating biocides | Microbiological and biofilm removal |
| Purging and filtration | Solids and sludge control |
| Polymer coatings | Selective corrosion protection |
| ORP, pH, conductivity sensors | Continuous and predictive monitoring |
The integration of linear corrosion meters, ER probes, and digital monitoring enables data-driven predictive strategies, reducing costs and preventing catastrophic failures.
Conclusion
Corrosion in cooling systems is a multifactorial phenomenon governed by physicochemical, thermodynamic, and biological parameters. Its management requires chemical control, inhibition, microbiological sanitation, and continuous monitoring. Strict application of integrity engineering prevents thickness loss, heat loss, leaks, and environmental risks.
References
- Meesters, K. P. H. (2003). Biofouling reduction in recirculating cooling systems. Desalination, 153(1–3), 233–242.
- Di Pippo, F., Di Gregorio, L., Congestri, R., Tandoi, V., & Rossetti, S. (2018). Biofilm growth and control in cooling water industrial systems. FEMS Microbiology Ecology, 94(5), fiy044. https://doi.org/10.1093/femsec/fiy044
- Hsieh, M.-K., Li, H., Chien, S.-H., Monnell, J. D., Chowdhury, I., & Dzombak, D. A. (2010, December). Corrosion control when using secondary treated municipal wastewater as alternative makeup water for cooling tower systems. Water Environment Research, 82(12), 2346–2356. https://doi.org/10.2175/106143010X12681059117094