Page 178 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

4.14 CHAPTER FOUR

TABLE 4.4 Prediction of Water Tendencies by the Langelier Index

Langelier saturation index Tendency of water
2.0 Scale-forming and for practical purposes noncorrosive
0.5 Slightly corrosive and scale-forming
0.0 Balanced, but pitting corrosion possible
–0.5 Slightly corrosive and nonscale-forming
–2.0 Serious corrosion

The most accurate method for calculating pHs is to use the following formula:
pHs = (9.3 + A + B) − (C + D) (4.3)
The numerical values of A, B, C, and D for substitution into Eq. (4.3) are found in Table 4.5.
A more empirical method to find pHs is to use the chart in Fig. 4.2.

RYZNAR STABILITY INDEX (RI)

Also referred to as simply the stability index (SI), the RI is an empirical method used to
predict scale-forming tendencies of water. The RI is calculated from the following formula
using the same definitions used for the LSI:
RI = 2 pHs − pH (4.4)

The RI is always positive. When it falls below 6.0, scale formation is possible and becomes
more probable with decreasing RI. For an interpretation of the RI, refer to Table 4.6.

TABLE 4.5 Numerical Values for Substitution in Eq. (4.3) to Find the pHs of Saturation of Water
Total solids A Ca as CaCO 3 C M alkalinity D

50–330 0.1 10–11 0.6 10–11 1.0
400–1000 0.2 12–13 0.7 12–13 1.1
14–17 0.8 14–17 1.2
Temp, °F B
18–22 0.9 18–22 1.3
32–34 2.6 23–27 1.0 23–27 1.4
36–42 2.5 28–34 1.1 28–35 1.5
44–48 2.4 35–43 1.2 36–44 1.6
50–56 2.3 44–55 1.3 45–55 1.7
58–62 2.2 56–69 1.4 56–69 1.8
64–70 2.1 70–87 1.5 70–88 1.9
72–80 2.0 88–110 1.6 89–110 2.0
82–88 1.9 111–138 1.7 111–139 2.1
90–98 1.8 139–174 1.8 140–176 2.2
100–110 1.7 175–220 1.9 177–220 2.3
112–122 1.6 230–270 2.0 230–270 2.4
124–132 1.5 280–340 2.1 280–340 2.5
134–146 1.4 350–430 2.2 350–440 2.6
148–160 1.3 440–550 2.3 450–550 2.7
162–178 1.2 560–690 2.4 560–690 2.8
178–194 1.1 700–870 2.5 700–880 2.9
194–210 1.0 880–1,000 2.6 890–1,000 3.0

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