Langelier Saturation Index (LSI) Calculator
Model calcium carbonate scaling potential and corrosive aggressiveness with Langelier Saturation Index (LSI) and Ryznar Stability Index (RSI).
Water Chemistry Inputs
LSI Scale Reference Guide
- LSI > +0.5: Scale forming (CaCO3 supersaturated, will precipitate)
- -0.5 ≤ LSI ≤ +0.5: Neutral / Balanced (slight scale protection)
- LSI < -0.5: Corrosive / Undersaturated (dissolves metals)
Saturation & Stability Indices
Carrier Empirical Formula Constants
Chemical Treatment Recommendation
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
What is the Langelier Saturation Index (LSI) and what does it predict?
The LSI is an equilibrium model derived from calcium carbonate solubility. It indicates whether water will precipitate calcium carbonate (forming mineral scale deposits when LSI > 0) or dissolve protective carbonate coatings and attack metal piping (causing corrosion when LSI < 0).
Why does warmer water scale faster than cold water?
Calcium carbonate exhibits retrograde (inverse) solubility—unlike most salts that dissolve better in hot water, CaCO3 becomes significantly less soluble as water temperature increases. Consequently, heat exchanger surfaces and boiler feed heaters scale first.
What is the difference between the LSI and the Ryznar Stability Index (RSI)?
The LSI is purely qualitative and indicates directional equilibrium (scale vs corrosive). The Ryznar Stability Index (RSI = 2×pHs - pH) is an empirical index based on physical observation in municipal pipes. RSI values between 6.0 and 7.0 indicate stable water, values below 5.5 indicate heavy scaling, and values above 8.0 indicate severe corrosion.
How is LSI controlled in industrial cooling towers and RO systems?
To prevent scaling without wasting huge volumes of blowdown water, operators either inject sulfuric acid to destroy bicarbonate alkalinity (lowering pH), or dose polymeric threshold antiscalant inhibitors that distort CaCO3 crystal lattices, allowing safe operation at LSI values up to +2.5.