Stiff-Davis CaCO₃ + Templeton / Marshall-Slusher / Jacques-Bourland Sulfates
Stiff-Davis derivation, sulfate Ksp correlations, ionic-strength effects, incompatibility, inhibitor chemistry.
Ionic strength:
Stiff-Davis Stability Index (CaCO₃, high-TDS):
K from Stiff-Davis 1952 chart, interpolated by T and ionic strength.
Sulfate saturation ratio (general):
BaSO₄ Ksp — Templeton 1960:
Severity bands:
SSI > +0.5 → scaling | −0.5 to +0.5 → stable | < −0.5 → corrosive
SR < 1 → undersaturated | 1–2 → mild | 2–10 → moderate | > 10 → severe
Stiff-Davis: SSI = pH − pCa − pAlk − K(T, I). Positive SSI → scaling, negative → CO₂-aggressive corrosive.
Saturation ratio SR = [Ba²⁺][SO₄²⁻] / Ksp(T, I) using the Templeton 1960 correlation. SR > 1 → barite will precipitate; > 10 → severe.
Continuous phosphonate or polyacrylate (5–25 ppm) when any scale shows SSI > 0.5 or SR > 2. Squeeze for SR > 10 (especially barite).