What Is The Problem With Aluminum Corrosion in Cooling Towers?
Aluminum is lightweight, easy to tool and has been used in many industries for years. Unfortunately, aluminum has different solubility and corrosion resistance characteristics than most materials common to cooling towers and recirculating water systems.
Most water treatment strategies are designed to address corrosion and scaling concerns on a variety of materials, but water chemistry that protects metals like steel and copper can present an aggressive situation on aluminum. Aluminum is a very stable metal in dry air, but aluminum components treated by recirculating water systems is another matter.
What Is The Solution for Aluminum Corrosion In Cooling Towers?
The corrosion rate of aluminum increases when the pH of the water exceeds 8.0 and becomes severe when the pH exceeds 8.4. A treatment program designed to protect aluminum components should maintain the pH of the water between 7.5 and 8.0. Unfortunately, this has an adverse effect on ferrous metals in the system.
The corrosion rate of iron is elevated significantly in this neutral pH range. One must carefully weigh the benefits of a neutral pH program for systems constructed primarily of ferrous metals against the cost of replacing aluminum components with plastic or brass pieces.
When the cost favors a neutral pH program designed to protect expensive aluminum components such a mold(s), the acid must be used to maintain the pH of the water within the 7.5 – 8.0 range. Chardon cooling tower treatment may feed using the inhibitor relay, although a controller capable of controlling based on pH offers the most reliable solution. For systems with accurate pH control, we will offer a specialized corrosion protection program and maintain the feed rate between 1.0 and 1.5 ppm as zinc.
Systems with softened make-up present an additional problem. The combination of low calcium hardness and low pH can significantly accelerate corrosion on ferrous metals. To prevent this combination from corroding the system, soft water can be blended with unsoftened water to deliver approximately 100 ppm of calcium hardness in the system water.
What About Automotive Antifreeze For Aluminum Engine Blocks?
Silicate-based corrosion inhibitors will form passivation films on aluminum and reduce corrosion, but these products also form silica scale on heat exchangers. The effect of silica scale on heat transfer is nine times as great as calcium scale and this technology is rarely used in industrial applications.