Scale


Scale is probably the most widely associated problem in cooling water systems. This term has become so generic that it is often applied incorrectly to all solid accumulations in the system. Scale, as originally defined, forms by crystallization of a dissolved salt when its concentration exceeds its solubility. Most scale forming compounds have the unusual property of becoming less soluble as the water temperature increases. Because of this, scale will generally deposit at the heat of the exchange surface and water interface-the very place which should be kept scale-free for efficient heat transfer to take place.



The most common scale will usually consist of calcium carbonate. Its ingredients, calcium and alkalinity, are present in all natural water. For any given water composition and temperature, the tendency to form calcium carbonate scale can be predicted from the temperature, pH, calcium hardness, total alkalinity, and the total dissolved solids (TDS). This prediction calculates when a water of known composition would be in equilibrium with calcium carbonate at the indicated temperature. The calculation is further correlated with field experience data to give a better picture of what might be expected of a given water under the specified conditions. The final answer is referred to as the Stability Index. A number below 6.0 indicates scale will form, and become more pronounced the lower the index number, while as the number rises above 7.0, the water is said to be increasingly corrosive.



Initial Conditioning | Scale | Fouling | Corrosion | Microbiological Control | Cooling Water Treatment
 
 
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