A Primer on the Complexity of Different Scale Deposits

Complexity of HVAC Scale Deposits

Last week, Tim Fregeau, Goodway’s Director of Sales, Liquid Solutions Division, hosted a webinar titled  “Scale: Why You Have It, What It Does and How to Descale Safely and Effectively“. During the presentation, Tim discussed the importance of knowing what type of scale you have. Due to the complex nature of many scale deposits, it is important to identify them correctly, and in the end, this can save time and money.

Different types of Scale

Here’s a breakdown of the common types of scale you might find in your industrial equipment:

  • Calcium: Calcium carbonate is a white chalky substance that is formed when calcium ions in water react with carbonate ions to form limescale. This one of the more common types of scale.
  • Magnesium: Another common type of scale found in industrial equipment is magnesium, a white solid that has a low solubility in water.
  • Barium salts: Barium chloride is a soluble salt that forms a hard black deposit in the form of scale. While not as common as calcium and magnesium scale deposits, it is still found in process equipment and requires identification to properly treat.
  • Silicate: Another salt that can form hardened scale deposits in high pH conditions. Metal silicates are also thought to cause other types of scale to form faster.
  • Phosphate: An inorganic molecule containing phosphorus and oxygen which can combine with calcium or aluminum to cause heavy scaling. Like silicate, this is compounded by the presence of calcium and magnesium in a solution.  
  • Rust: While technically not scale, rust can also be removed with descaling. Rust is generally a result of corrosion taking place from some point within the system.  Sometimes, it can be a result of iron-rich groundwater as well.

Causes of Different Scale Development

As you see, there are several types of scale build-up, with calcium carbonate, or limescale, being the most common. But how does it get in your process equipment? The salts alone are not enough to form scale, but when various conditions are applied, they can separate from it and form hard scale. These conditions are:

  • High mineral concentration (hard water): This is when water contains high levels of minerals, in the form of calcium or magnesium. These saturated solutions easily lose ions when other conditions such as heat and pH play a factor.
  • High temperature: High-temperature water that contains certain minerals (in particular, calcium and magnesium) will fall out of solution (precipitate) and can cause these minerals to form hard adherent scale.  
  • pH: pH is the measure of the acidity or alkalinity of a substance.  A lower PH value is associated with acidic solutions whereas higher pH’s are associated with alkaline solutions.
  • Dropped pressure: System pressure plays a key factor in scale build up. A drop in pressure allows the mineral salts in suspension to drop out and form scale.
  • Decreased flow velocity: While suspended flow of process water allows the time for water to become heated and deposits to form, accumulation of scale requires a constant flow. A steady flow of mineral-laden process water can provide an infinite supply of the salts that cause scale.
  • Accumulation of impurities: While other nonmetallic impurities alone may not become scale, the concentration of them in process water can contribute to scale by increasing pH levels of water and saturation of water.

How to Choose the Right Descaling Approach

Your method for descaling depends on the type of scale, its thickness, and where it’s located. For example, wire brushes can be used to remove deposits that generally cannot be removed with chemical descaling, like deposits comprised of phosphates and silicates.  Many types of scale deposits are soluble in chemical solutions–however, keep in mind, different types of scale will respond differently to different chemicals. More importantly, certain chemical compounds could create corrosion in your equipment. As a result, Goodway’s Scalebreak SS,  formulated specifically to descale stainless steel is void of hydrochloric acid, because the chloride ions in hydrochloric acid, can create stress cracking corrosion in stainless steel.

Knowing the kind of scale you have and taking into consideration the type of equipment it is on is essential to getting rid of it. Choosing the wrong descaling method or product could lead to wasted time and money or damaged equipment. Speak to a professional about your particular situation to find the best method, product and procedure that can remove scale safely and effectively. To get a detailed consultation about how to best descale your equipment, reach out to the Goodway Technologies experts at 1-800-333-7467.

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Photo Source: Wikimedia Commons

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