Larson-Skold Index

Definition

The Larson-Skold Index estimates the corrosivity of water toward mild steel as the ratio of aggressive anions (chloride plus sulfate) to protective inhibitors (bicarbonate plus carbonate). It is computed in milliequivalents per liter.

LS equals (Cl- plus SO4 2-) divided by (HCO3- plus CO3 2-) in meq/L, with conversions of chloride mg/L divided by 35.5, sulfate divided by 48, and alkalinity as CaCO3 divided by 50. An index below 0.8 indicates lower corrosion risk with a likely stable passive film, 0.8 to 1.2 indicates potential risk of film interference, and above 1.2 indicates high risk with likely localized corrosion and pitting. It quantifies the sabotage of protective film formation but does not by itself predict corrosion rate.

Related concepts

Film Saboteurs · Alkalinity · Ryznar Stability Index

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Part of The Blueprint of Water · 📏 measurement