Parameter Remarks
10 Sulphates Rejection < 2000 ppm. To be measured for calculating RSI.
11 Chemical Corrosion Index Index = (Chlorides + Sulphates + Nitrates) / (M-Alkalinity) (all
expressed in meq/l)
15 Ammonium limit not applicable for Cu-free systems
16 Suspended Solids (max
10µ)
No particles > 10µ allowed. (Particles <0.5µ not considered).
18 Biology Anaerobic biology in closed system never allowed.
Ryznar Stability Index (RSI)
The Ryznar Stability Index (RSI) is a parameter for predicting whether water will tend to dissolve
or precipitate calcium carbonate. The adhesion of scaling deposits and their effect are different
on different materials, but the equilibrium of the water (scaling or corrosive) is only determined by
its actual pH value and by the saturation pH value (pH
s
).
The saturation pH value is determined by the relationship between the calcium hardness, the
total alkalinity, the total solids concentration and the temperature.
The Ryznar Stability Index is calculated as follows :
RSI = 2*pH
s
- pH
Symbol Explanation
pH Measured pH (at room temperature) of water sample
pH
s
pH at saturation
The pH
s
is calculated by using :
pH
s
= (9.3 + A + B) - (C + D)
Symbol Calculation
A
(
10
log(TDS) - 1) / 10
B
13.12 x
10
log(°C+273) + 34.55
C
10
log(Ca
2+
) - 0.4 (Ca
2+
expressed as ppm CaCO
3
)
D
10
log(M-Alkalinity) (M-Alkalinity expressed as ppm CaCO
3
)
RSI and chloride limitation
Single Pass system
RSI Chloride
limit
Water condition Maximum 65°C /
149°F
Maximum 95°C / 203
°F
RSI<3.9 200 ppm Very high scale formation Water cannot be used. Not applicable.
Instruction book
9829 3178 63 73
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