Puckorius (Practical) Scaling Index

Paul Puckorius argued in the 1980s that measured pH is the wrong number to put in a scaling index for recirculating cooling water. Bulk pH drifts with dissolved CO₂, with acid feed swings, and with whatever the tower stripped out of the air that afternoon — but the water's real buffering capacity, and therefore the pH it will settle back to at the hot metal surface, is set by alkalinity. So he substituted an equilibrium pH, $\mathrm{pH}_{\text{eq}}$ = 1.465·log₁₀(alkalinity as CaCO₃) + 4.54, and kept Ryznar's doubling. With $\mathrm{pH}_s$ = 7.31 and alkalinity 180 mg/L, $\mathrm{pH}_{\text{eq}}$ = 1.465 × 2.255 + 4.54 = 7.84 and PSI = 14.62 − 7.84 = 6.78.

Read PSI on the Ryznar scale: under about 6 scaling, 6–7 balanced, over 7 corrosive. Where it earns its keep is in high-cycle towers dosed with acid, where the operator has pushed pH down to 7.0 but the alkalinity is still 300 mg/L — LSI and RSI both look fine while the exchanger scales, because the surface pH never actually stayed at 7.0. The trap is feeding it alkalinity in raw bicarbonate mg/L instead of as CaCO₃; the 0.82 conversion factor is a fifth of a PSI unit and will flip your verdict.