Water scale is a deposit found on surfaces that associate with hard water. This is when water contains bicarbonates or carbonates of magnesium or calcium, and is therefore a lot more likely to cause water scale. During water evaporation or heating, the scale minerals deposit a rocklike precipitate within the water heaters, pipes, equipment and on glassware and fixtures. The most widespread scale is caused by calcium carbonate but a variety of different scales are often found in water, caused by combinations of different ions.

When water scale is present, efficiency of the heat exchangers is reduced because their heat transfer surfaces are now insulated. In cooling water systems, the most common scale form is calcium carbonate (CaCO₃). Inside the water, the calcium ions and bicarbonate combine to form calcium bicarbonate:

Ca⁺⁺ + 2HCO -> Ca(HCO₃)₂

If water scale deposits accumulate, the flow of water is restricted and heat transfer surfaces and piping become plugged. If scale depositions are ignored, the result can be destruction or failure of the heat exchanged tubes. Efficiency loss aside, process contamination can occur.

Evidence of Water Scale

Water scale is most commonly recognized as hard white or off white deposits, building up on showerheads, drains and taps. Deposits are left on glassware, dishes, sinks and countertops that have just been washed.

Large scale problems are found in cooling towers, causing industries around $1 billion a year to remove. Irrigation systems, car washes, boilers and evaporative coolers all experience water scale issues. Due to the coating formed by water scale, thermo-transfer is greatly affected and fluid flow is reduced, enormously increasing fuel costs due to water scale build up.

Due to water scale depositions, industries experience losses of billions of dollars through unplanned shutdowns, high product rejection rate, expensive parts replacement, process contamination, etc.

Current Methods to Prevent Fouling

• Permanent magnets
• Ion-exchange
• Inhibitors – algae, scale, bacteria, rust
• Phosphates
• Electric conditioning

These methods don't fully prevent or remove sedimentation build up, but they are successful in slowing down the scaling process.

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