Cooling Tower Failure Library

Understanding Cooling Tower Failures

Cooling towers are exposed to the environment, making them susceptible to scaling, biological growth, corrosion, and mechanical failures. Many failures are preventable through water treatment and maintenance.

Scale Formation

Scale deposits on the fill and internal surfaces, reducing heat transfer and airflow, and eventually blocking the tower.

• Symptoms: Reduced cooling capacity, increased approach temperature (difference between cold water and wet-bulb), visible scale on fill, and reduced airflow.
• Root causes: High cycles of concentration (inadequate blowdown), high hardness in makeup water, high pH, and high water temperature (calcium carbonate is less soluble at higher temperatures).
• Prevention: Maintain correct cycles of concentration by blowdown, add scale inhibitor (phosphonate), soften the makeup water if hardness is very high, and control pH. Monitor conductivity and blow down automatically.

Biological Fouling and Legionella

Cooling towers are ideal environments for biological growth, including the deadly Legionella bacteria. Biofilm also reduces heat transfer and causes under-deposit corrosion.

• Symptoms: Slime on fill and basin, green or brown discoloration of water, foul odour, reduced heat transfer, and in severe cases, Legionella outbreak.
• Root causes: Inadequate biocide dosing, stagnant water (during shutdown), warm water temperature (25–45°C is ideal for Legionella), sunlight exposure (algae growth), and nutrients in the water.
• Prevention: Maintain continuous biocide dosing (alternating oxidising and non-oxidising biocides), maintain residual biocide level, prevent stagnation (circulate even at low load), clean the tower regularly, and test for Legionella periodically.

Corrosion

Corrosion attacks the tower structure, fill support, basin, and piping, causing leaks and structural failure.

• Symptoms: Rust on metal components, pitting in the basin, leaking pipework, degraded structural supports, and eventual structural failure.
• Root causes: Inadequate corrosion inhibitor, high dissolved oxygen (aerated water), low pH (acidic water), galvanic corrosion (dissimilar metals), and high TDS from high cycles of concentration.
• Prevention: Add corrosion inhibitor (phosphate, azole), control pH (7.5–8.5), maintain correct cycles of concentration, use compatible materials (fibreglass, stainless, or coated steel), and apply protective coatings.

Drift Eliminator Failure

Drift eliminators reduce water droplet carryover in the exhaust air. If they fail, water is lost and droplets can carry bacteria (including Legionella) into the surrounding area.

• Symptoms: Visible water droplets in the exhaust plume, water loss, ice formation in cold climates (on nearby structures), and potential health risk from drift.
• Root causes: Broken or degraded drift eliminators (UV damage, ageing), incorrect installation (gaps between eliminator panels), and biological fouling.
• Prevention: Inspect and replace drift eliminators on schedule, install UV-resistant eliminators, ensure correct installation without gaps, and clean eliminators during tower maintenance.

Fan and Motor Failure

Cooling tower fans and motors fail from bearing wear, belt failure, imbalance, and corrosion.

• Symptoms: Increased noise and vibration, reduced airflow, motor overheating, and eventual fan failure.
• Root causes: Bearing wear (inadequate lubrication, contamination), belt failure (misalignment, wrong tension, ageing), blade imbalance (fouling, erosion, or damage), and corrosion of fan hub and blades.
• Prevention: Lubricate bearings on schedule, align and tension belts correctly, inspect and clean fan blades regularly, use corrosion-resistant fan materials (fibreglass, stainless), and balance the fan annually.