Scale Formation and Scale Forming Deposits
When water is heated or evaporated, insolubles are deposited on metal surfaces. These deposits usually occur on the metal in the cooling towers, evaporative condensers, or inside the pipes and tubes of the condenser water system which have a recirculation water system.
Calcium carbonate is the chief scale forming deposit found in cooling systems, but magnesium carbonate and calcium sulfate can also cause some degree of scaling.
The prime causes of scale formation can be attributed to these factors:
- Alkalinity: The higher the alkalinity of a particular water, the higher the bicarbonate and/or carbonate content. As these minerals approach saturation, they tend to come out of solution.
- Total Hardness (calcium + Magnesium): A higher concentration of hardness will increase the/tendency of calcium and magnesium salts to come out of solution. Scale will form on heat transfer surfaces when water containing even a small amount of hardness is used.
- Total Dissolved Solids (TDS): The higher the solids content, the greater the tendency to precipitate the least soluble of these solids.
- Temperature: The higher the temperature, the greater the tendency to precipitate the calcium and magnesium salts because of their property of inverse solubility (where a rising temperature decreases the solubility). Sodium compounds such as table salt (sodium chloride), on the other hand, have a direct solubility (where a rising temperature increases solubility).
- pH: The higher the pH value, the greater the carbonate content of the water (pH means potential hydrogen). When a hydrogen atom has lost its electron (H+), it becomes a positive hydrogen ion. When a great many of these hydrogen atoms make this change, the solution will become highly acid and attack metals. When the hydrogen atom gains electrons, the solution will be base and have a pH value from 7.1 to 14. A base solution contains more hydroxyl ions (OH-). Scale will form when a base solution is exposed to a temperature rise, providing the hardness is 200 parts per million or higher.
Scale deposits can cause the following problems in cooling water systems:
- Reduced heat transfer decreasing the heat transfer efficiency
- Increased pressure drop on water side
- Under Deposit Corrosion
Click here to review our cooling tower product selection or here for our boiler product selection or here to contact us.
