-20-
Appendix
Unfavorably high total ionized solids (TIS) can accelerate the rate of galvanic corrosion. These contami-
nants can function as electrolytes which increase the potential for galvanic cell corrosion and lead to
localized corrosion such as pitting. Eventually, the pitting could become so extensive that leaking will
occur between the process water and facility water diminishing the System's heat transfer capability.
High water hardness (Calcium and Maganese) can also produce scaling. Scaling will inhibit heat transfer
between the process and facility side by building up a deposit layer on metal surfaces. As an example,
raw water in the United States averages 171 ppm (of NaCl). The recommended level for use in a water
system is between 0.5 to 5.0 ppm (of NaCl).
Recommendation: Initially fill the tank with distilled/deionized water. Do not use untreated tap water as
the total ionized solids level may be too high.
Maintain this water quality at a resistivity of between 1 to 10 megohm-cm (compensated to 25°C) by
using a purification system. Although the initial fill may be as high as 10 megohm-cm (compensated to
25°C), the desired level for long time usage is 1 to 3 megohm-cm (compensated to 25°C).
The above two recommendations will reduce the electrolytic potential of the water and prevent or reduce
the galvanic corrosion observed.
Water Quality Standards
and Recommendations
Permissible (PPM)
Desirable (PPM)
Microbiologicals
(algae, bacteria, fungi)
0
0
Inorganic Chemicals
Calcium
<40
<0.6
Chloride
250
<25
Copper
<1.3
<1.0
Iron
<0.3
<0.1
Lead
<0.015
0
Magnesium
<12
<0.1
Manganese
<0.05
<0.03
Nitrates\Nitrites
<10 as N
0
Potassium
<20
<0.3
Silicate
<25
<1.0
Sodium
<20
<0.3
Sulfate
<250
<50
Hardness
<17
<0.05
Total Dissolved Solids
<50
<10
Other Parameters
pH
6.5-8.5
7-8
Resistivity
0.01*
0.05-0.1*
* Megohm-Cm (Compensated to 25°C)
15.00
10.00
3.00
1.00
0.10
0.05
Resistivity (megohm-cm @ 25°C)
Not Recommended, Increasingly Corrosive
Operations with Stainless Steel Systems
Operations with
Mixed Metals
Copper/Brass/
Stainless Steel
CONSULT MATERIALS ENGINEER
10
20
30
40
50
60
70
80
Water Quality Considerations
°C
Summary of Contents for NESLAB System IV
Page 19: ... 18 Section VII Diagrams Flow Diagram ...
Page 20: ... 19 Rear View ...
