Estimate scale potential from pH, hardness, alkalinity, and TDS. Use engineering-ready indices and guidance. Export reports for audits and teams quickly.
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| Case | pH | TDS (mg/L) | Temp (°C) | Ca Hardness (mg/L as CaCO3) | Alkalinity (mg/L as CaCO3) | pHs | LSI | RSI | Interpretation |
|---|---|---|---|---|---|---|---|---|---|
| A | 8.20 | 850 | 35.0 | 180 | 120 | 7.456 | 0.744 | 6.712 | High scaling tendency |
| B | 7.40 | 500 | 25.0 | 80 | 70 | 8.207 | -0.807 | 9.014 | High corrosion tendency |
| C | 9.00 | 1,200 | 45.0 | 250 | 150 | 7.049 | 1.951 | 5.099 | High scaling tendency |
Mineral deposits reduce heat-transfer efficiency, increase pressure drop, and accelerate under-deposit corrosion. A CaCO3 layer can raise energy use and trigger higher approach temperatures in condensers and plate exchangers. This calculator converts routine water-test inputs into saturation indicators that help prioritize treatment, cleaning intervals, and inspection scope across boilers, cooling loops, and closed circuits. Results are useful for trending and for explaining risk to maintenance and production teams.
Most open-recirculating cooling systems run pH 7.2–9.0, alkalinity 60–200 mg/L as CaCO3, calcium hardness 50–300 mg/L as CaCO3, and TDS 300–2,500 mg/L. Boilers often use tighter hardness control but higher temperature. Temperature strongly shifts equilibrium; the same chemistry at 25°C can be less stable at 45°C. Record sampling point, cycles of concentration, and recent chemical feed changes to keep comparisons meaningful.
Saturation pH (pHs) estimates the pH where calcium carbonate is in balance for the given TDS, temperature, alkalinity, and hardness. LSI = pH − pHs: positive values suggest scale potential, while negative values suggest corrosion potential. RSI = 2·pHs − pH adds operational context; lower RSI generally indicates scaling risk, while higher RSI indicates corrosive water. Track both indices over time instead of relying on a single snapshot.
Use the results as a screening layer, then confirm with plant evidence. If LSI is ≥ 0.2, review cycles of concentration, verify antiscalant dosage, and consider softening, acid feed, or blowdown changes. If LSI is ≤ −0.2, verify inhibitor programs and check metal loss indicators such as coupons, LPR probes, and iron trends. Export CSV for spreadsheets and the PDF summary for audits or contractor scope.
Indices assume carbonate scaling dominates and inputs are representative. Verify units as “mg/L as CaCO3” for hardness and alkalinity; convert if your lab reports meq/L or ppm as Ca2+. Field errors, stratified sampling, and transient chemistry can distort results, especially during startups and cleaning events. Very high TDS, unusual ions, or silica scaling may require specialized models. Always correlate with deposit samples, ultrasonic thickness, and exchanger performance trends before major operational changes.
A positive LSI indicates the water is supersaturated with respect to calcium carbonate and may deposit scale on heat-transfer surfaces, especially at higher temperatures and higher cycles.
A negative LSI suggests the water is undersaturated for calcium carbonate, so it may dissolve protective films and increase corrosion tendency, depending on metallurgy and inhibitor control.
Use RSI as a complementary stability check. Lower RSI values usually align with scaling risk, while higher RSI values align with corrosive conditions. Trending both improves confidence versus a single reading.
Enter calcium hardness and alkalinity as mg/L expressed as CaCO3. If your lab reports meq/L, convert using 50 mg/L as CaCO3 per meq/L before input.
No. These indices primarily address carbonate equilibrium. If silica, sulfate, or mixed deposits are dominant, use specialized solubility models and confirm with deposit chemistry.
Temperature shifts carbonate equilibria and affects the saturation pH calculation. Using a realistic operating temperature is essential, especially for exchangers, hot wells, and boiler feed sections.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.