What is langelier saturation index (lsi)?
The LSI predicts whether cooling water will deposit scale or corrode metal, calculated from pH, temperature, calcium hardness and alkalinity. A positive index means the water tends to scale; negative means it tends to corrode. Treatment programmes aim to hold it slightly positive.
Also called: LSI, saturation index
The index compares actual pH with the pH at which calcium carbonate would be exactly saturated. Above that point calcium carbonate precipitates as scale; below it, the water is aggressive and will attack pipework and heat-exchanger tubes.
Neither extreme is acceptable, which is why treatment targets a small positive value: enough for a protective microscopic carbonate film, not enough for insulating scale. Scale inhibitors widen that acceptable window considerably.
LSI is a tendency, not a rate, and it does not account for biofilm, suspended solids or localised hot spots. It is a control input alongside conductivity, hardness and biological monitoring — not a complete programme on its own.
