Langelier Index

The Langelier Saturation Index (LI), a measure of a solution’s ability to dissolve or deposit calcium carbonate, is often used as an indicator of the corrosivity of water. The index is not related directly to corrosion, but is related to the deposition of a calcium carbonate film or scale; this covering can insulate pipes, boilers, and other components of a system from contact with water. When no protective scale is formed, water is considered to be aggressive, and corrosion can occur. Highly corrosive water can cause system failures or result in health problems because of dissolved lead and other heavy metals.

An excess of scale can also damage water systems, necessitating repair or replacement. In developing the LI, Langelier derived an equation for the pH at which water is saturated with calcium carbonate (pHs). This equation is based on the equilibrium expressions for calcium carbonate solubility and bicarbonate dissociation. To approximate actual conditions more closely, pHs calculations were modified to include the effects of temperature and ionic strength.

The Langelier Index is defined as the difference between actual pH (measured) and calculated pHs. The magnitude and sign of the LI value show water’s tendency to form or dissolve scale, and thus to inhibit or encourage corrosion. Although information obtained from the LI is not quantitative, it can be useful in estimating water treatment requirements for prevention of scale build-up in piping, as well as serving as a general indicator of the corrosivity of water. For treatment siliphos is normally introduces into the system by using a refillable cartridge and fill it up with siliphos balls. Siliphos is a water treatment compound, a glass-like Polyphosphate containing Sodium, Calcium Magnesium and Silicate, formulated specifically for the treatment of water problems. It originates from the milk thistle seed. The siliphos dissolves into the water and forms a microscopic layer onto the metal, preventing corrosion and the building up of scale. Siliphos will also slowly remove existing scale from old pipes. All components used in Siliphos are 100% pure food grade materials.

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