Corrosion Inhibitor Efficiency
Calculate the efficiency of a corrosion inhibitor, η = (CR₀ − CR_inh) ÷ CR₀ × 100%, comparing the corrosion rate without inhibitor (CR₀) with the rate in its presence (CR_inh). The result, in %, measures how much the inhibitor slowed corrosion — the standard indicator to evaluate and compare inhibitors in laboratory tests (mass loss, polarization or impedance). Effective inhibitors form protective films on the surface and reach efficiencies above 90%. It is widely used in boiler water treatment, cooling systems and well acidizing. Enter the corrosion rates without and with inhibitor.
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Corrosion inhibitor efficiency
A corrosion inhibitor is a substance that, added to the medium in small concentration, sharply lowers the corrosion rate of a metal — usually by forming a protective film adsorbed on the surface that blocks the anodic reaction, the cathodic one, or both. To evaluate and compare inhibitors, the inhibition efficiency is measured: η = (CR₀ − CR_inh) ÷ CR₀ × 100%, comparing the corrosion rate without the inhibitor (CR₀) with the rate in its presence (CR_inh). An efficiency of 80% means the inhibitor cut corrosion down to a fifth of the original value. The corrosion rates fed into the calculation may come from different techniques — weight-loss coupon tests, linear polarization resistance (LPR) measurements or electrochemical impedance spectroscopy — and the efficiency is usually mapped against inhibitor concentration to find the optimum dose (beyond which extra product adds very little). High-performance inhibitors go past 90–95% efficiency. They are widely used in the treatment of boiler water and cooling towers, in oil and gas systems, in well acidizing (where they protect the tubing during acid injection) and in metal pickling. Enter the corrosion rates without and with the inhibitor.
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Larson-Skold Index (Water Corrosivity)
Computes the Larson-Skold index, the ratio between the aggressive and the protective anions in a water: chloride plus sulphate divided by alkalinity, all converted to milliequivalents per litre with the equivalent weights 35.45 for chloride, 48.03 for sulphate and 50.04 for alkalinity expressed as CaCO₃. The reading is direct: below 0.8 alkalinity dominates and the carbonate film protects carbon steel; between 0.8 and 1.2 corrosion stops being negligible; above 1.2 chloride and sulphate break the film and the localised corrosion rate takes off, the typical scenario of cooling tower makeup water running at many cycles of concentration. Unlike the Langelier index, this one does not say whether the water will scale — it measures only the corrosive power of the anions, which is why the two readings complement each other rather than compete. Total alkalinity was adopted as the input, instead of separate bicarbonate and carbonate, because that is what a routine laboratory reports, and converting it through the CaCO₃ equivalent returns exactly the sum of the two in milliequivalents per litre. Enter the chloride, the sulphate and the total alkalinity.
Chlorine Demand
Calculate the chlorine demand of a water, demand = applied dose − chlorine residual, subtracting the measured chlorine residual (mg/L) from the applied chlorine dose (mg/L). The result, in mg/L, is the chlorine consumed by organic matter, ammonia, iron, manganese and other reducers before free chlorine remains for disinfection. Knowing the demand is essential to dose chlorine correctly and keep an adequate residual in the network without waste or underdosing. Enter the applied dose and the measured residual.
Hydraulic Retention Time (HRT)
Calculate the hydraulic retention time (HRT) of a reactor or tank, HRT = volume ÷ flow, dividing the working volume (m³) by the influent flow (m³/h). The result, in hours, is the average time the liquid stays in the unit and is decisive in designing clarifiers, anaerobic reactors, lagoons and aeration tanks: short times prevent reactions or settling from completing, while long times raise cost and footprint. Enter the working volume and the inlet flow.
Corrosion Rate (Mass Loss)
Calculate the corrosion rate by the mass-loss method, CR = 87.6 × W ÷ (D × A × t), from the mass loss W (mg), the material density D (g/cm³), the exposed area A (cm²) and the exposure time t (hours). The result, in mm/year, is the average speed at which the metal is consumed by corrosion — the key parameter to predict the service life of structures, piping and equipment and to set the corrosion allowance in design. Rates below 0.1 mm/year are usually acceptable. Enter the mass loss, density, area and time.
Velocity Gradient (Mixing)
Calculate the mean velocity gradient (G) in rapid-mix and flocculation chambers, G = √(P ÷ (μ × V)), from the dissipated power (W), the water dynamic viscosity (Pa·s) and the chamber volume (m³). The result, in s⁻¹, measures mixing intensity: rapid mixing needs high G (700–1000 s⁻¹) to disperse the coagulant, while flocculation uses low G (20–70 s⁻¹) to promote floc collision and growth without breaking them. Enter power, viscosity and volume.
Coagulant Dosing
Calculate the coagulant consumption of a water treatment plant, consumption = flow × dose ÷ 1000, multiplying the treated flow (m³/day) by the coagulant dose (mg/L) set by jar test. The result, in kg/day, sizes the storage, dilution and dosing pumps for products such as aluminium sulphate, ferric chloride or PAC, ensuring efficient coagulation of colloidal particles. Enter the treated flow and the coagulant dose.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.