Atlas Copco ZR 200 Instruction Book page 70

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
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 - pH
s
Symbol
pH
pH
s
The pH is calculated by using :
s
pH = (9.3 + A + B) - (C + D)
s
Symbol Calculation
A
10
( log(TDS) - 1) / 10
B
13.12 x
C
10
log(Ca
D
10
log(M-Alkalinity) (M-Alkalinity expressed as ppm CaCO
RSI and chloride limitation
Single Pass system
RSI
RSI<3.9
4.0<RSI<5.5
5.6<RSI<6.2
6.3<RSI<6.8
68
Explanation
Measured pH (at room temperature) of water sample
pH at saturation
10
log(°C+273) + 34.55
2+ 2+
) - 0.4 (Ca expressed as ppm CaCO
Chloride Water condition
limit
200 ppm Very high scale formation
200 ppm High scale formation
350 ppm Slight scale formation
500 ppm Neutral water
).
s
)
3
)
3
Maximum 65°C /
149°F
Water cannot be used. Not applicable.
Regular control and
descaling operation
necessary.
Not recommended for
plate heat exchangers
Water treatment not
necessary.
Occasional inspection
recommended.
Water treatment not
necessary.
Occasional inspection
recommended.
Instruction book
Maximum 95°C / 203
°F
Not applicable.
Not applicable.
Water treatment not
necessary.
Occasional inspection
recommended.
AIF999999