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Ryznar Stability Index (RSI)
The Ryznar stability index (RSI) attempts to correlate an empirical database of scale thickness observed in municipal water systems to the water chemistry. Like the LSI, the RSI has its basis in the concept of saturation level. Ryznar attempted to quantify the relationship between calcium carbonate saturation state and scale formation. The Ryznar index takes the form:
RSI = 2(pHs) - pH
Where:
- pH is the measured water pH
- pHs is the pH at saturation in calcite or calcium carbonate
The empirical correlation of the Ryznar stability index can be summarized as follows:
- RSI << 6 the scale tendency increases as the index decreases
- RSI >> 7 the calcium carbonate formation probably does not lead to a protective corrosion inhibitor film
- RSI >> 8 mild steel corrosion becomes an increasing problem.
Some other saturation indices that have found wide acceptance:
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