Corrosion in systems: causes and solutions

Corrosion is a serious threat to cooling tower and chiller systems, which can cause structural damage, leaks, downtime, and significant repair costs. Controlling corrosion is one of the main pillars of water treatment and maintenance.

From the list you provided, here are the types of corrosion that are highly relevant to cooling tower and chiller systems, along with their causes and solutions.

Types of Critical Corrosion in Cooling Tower and Chiller Systems

1. Oxygen Corrosion / Uniform Attack

• Description: This is the most common form of corrosion and often occurs evenly across the entire surface of metal exposed to water. Dissolved oxygen in water is the main trigger.

• Causes

  • Presence of Dissolved Oxygen: Water in cooling towers is constantly exposed to air, making it rich in oxygen.

  • Low pH (Acidic): Accelerates the corrosion reaction.

  • High TDS: Increases water conductivity, accelerating the flow of electrons in the corrosion reaction.

  • High Temperature: Increases the rate of chemical reactions.

• Solutions:

  • pH Control: Maintain water pH within the optimal range (typically 7.0−9.0) through chemical treatment.

  • Corrosion Inhibitor: Use appropriate corrosion inhibitors (e.g., molybdate, nitrite, phosphate) to form a passive protective layer on metal surfaces.

  • Corrosion-Resistant Materials: Select materials that are more resistant to oxygen corrosion.

2. Pitting Corrosion

• Description: A particularly dangerous form of corrosion because it occurs locally in small holes or ‘pits’ on the metal surface. The damage can be very deep and cause leaks without any significant indication of damage on the surface.

• Causes:

  • High Chloride Concentration: Chloride ions can damage the passive layer of metals (especially stainless steel) and trigger pitting.

  • Stagnant Water: Areas where water does not flow properly allow for differences in oxygen concentration, triggering local anodic and cathodic areas.

  • Fouling & Sediment: Deposits of dirt or scale can create areas of oxygen deprivation underneath, triggering pitting in the metal.

  • Damage to Protective Coatings: Defects in the passive layer or corrosion inhibitors.

• Solutions:

  • Chloride Control: Limit chloride concentrations through effective blowdown or water pre-treatment.

  • Corrosion Inhibitor Specific: Use inhibitors effective against pitting.

  • Adequate Water Flow: Ensure even water flow and avoid stagnant areas.

  • Regular Cleaning: Avoid sediment and fouling build-up with filtration (side stream filter) and cleaning.

3. Crevice Corrosion

• Description: Corrosion that occurs in narrow crevices or under gaskets, nuts, bolts, or between two contacting surfaces. Similar to pitting, it is also localised.

• Causes:

  • Narrow Crevices: Areas where oxygen in the water has difficulty reaching the metal surface, causing a difference in oxygen concentration between the crevice and the exposed surface.

  • Accumulation of Corrosive Ions: In crevices, chloride ions or other corrosive substances can become concentrated.

• Solutions:

  • Good Design: Minimise crevices in the design of cooling tower components and piping.

  • Proper Gaskets and Joints: Ensure that gaskets and joints are tight and properly installed.

  • Cleaning & Inspection: Regularly inspect and clean crevice areas.

  • Corrosion Inhibitor: As with pitting, effective inhibitors can help.

4. Galvanic Corrosion

• Description: Occurs when two different metals (with different electrochemical potentials) are electrically connected and exposed to an electrolyte (water). The more active metal (anodic) will corrode rapidly, protecting the more noble metal (cathodic).

• Causes:

  • Contact Between Two Different Metals: For example, copper pipes connected to carbon steel pipes, or brass fittings on steel components.

  • Water as an Electrolyte: Water in cooling towers acts as a conductive medium.

• Solutions:

  • Electrical Insulation: Use non-metallic insulating joints to separate different metals.

  • Select Compatible Metals: Use metals with similar electrochemical potentials.

  • Sacrificial Anodes: Use metals that are deliberately sacrificed (more anodic) to protect other metals.

  • Corrosion Inhibitor: Forms a protective layer on both metals.

5. Erosion-Corrosion

• Description: A combination of mechanical effects (abrasion due to high-velocity water flow or solid particles in the water) and chemical corrosion effects. The passive layer that protects the metal is continuously eroded, accelerating the rate of corrosion.

• Causes:

  • Very High Water Flow Velocity: Especially in pipe elbows, valves, or orifices.

  • Solid Particles in Water: Suspended particles (sand, silt, loose scale) that erode the metal surface.

  • Flow Turbulence: Highly turbulent water flow.

• Solutions:

  • Flow Velocity Control: Ensure pipe and pump designs maintain flow velocities within recommended limits.

  • Filtration: Use side stream filters or pre-filters to remove solid particles from the water.

  • Harder Materials: Consider harder materials or alloys that are more resistant to erosion-corrosion in vulnerable areas.

  • Smooth Flow Design: Avoid sharp changes in pipe direction or diameter.

Comprehensive Solutions from PT Jaya Sakti Internusa

Corrosion control requires a holistic approach. PT Jaya Sakti Internusa, with experience since 1998, provides complete solutions for your cooling towers and chillers:

• Comprehensive Water Analysis: Identifies corrosive potential and its causes.

• Chemical Treatment Best: Provision of appropriate corrosion and scale inhibitors.

• Filtration System: Installation of side stream filters and pre-filters to remove particles.

• Real-time Monitoring System: Use of controllers to continuously monitor pH, conductivity, and corrosion rate.

• Design & Upgrade: Ensuring proper design and upgrading to more corrosion-resistant materials if necessary.

With proper management, you can extend the service life of your assets and ensure the continued operational efficiency of your cooling system.