UFC 3-240-13FN
25 May 2005
b. EXAMPLE B-2:
Water from a cooling tower has a total alkalinity of 100 ppm (as CaCO3)
and a measured pH of 8.2 (same as example B-1). From Table B-7, the
pHeq is 7.47.
PSI = (2pHs) - (pHeq) = 2 (6.77) - 7.47
= 13.54 - 7.47 = 6.07
RSI = (2pHs) - (measured pH) = 13.54 - 8.2
= 5.34
LSI = (measured pH) - (pHs) = 8.2 - 6.77
= +1.43
c. The pHeq may also be calculated as follows:
pHeq = 1.485 log TA + 4.54
where TA denotes total alkalinity.
B-2.3
Scaling Severity Keyed to Indices
a. Commonly accepted interpretation of the previously described indices is
shown in Table B-8.
b. In Example B-2, the LSI predicted that the water would exhibit a severe to
very severe scaling tendency. The RSI predicted that the water would
exhibit a moderate to severe scaling tendency. The PSI predicted that the
water is stable with no tendency to form or dissolve scale.
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