UFC 3-240-13FN
25 May 2005
Figure 3-13. Effect of pH on Mild Steel and Copper Corrosion
100
10
1
5
10
9
8
7
6
pH
3-2.7.2
Estimating Carbon Dioxide in Steam. Corrosion engineers find it useful
to know the amount of carbon dioxide (CO2) in steam when assessing the return on
investment (i.e., cost savings from removing the CO2 versus the cost for use of internal
chemical treatment to remove the CO2). Engineers and water treatment service
companies need to estimate the amount of CO2 to properly estimate the amount of
neutralizing amine water treatment chemical that must be used. Example 3-5 illustrates
this estimation:
CO2 levels in the steam can be estimated from the amount of bicarbonate and
the carbonate alkalinity present in the feedwater as follows, where the "P" and "M"
alkalinity measure these compounds. (See paragraph 6-6.1 for test methods.)
EQUATION
CO2 = [bicarbonate x 0.79] + [carbonate x 0.35]
(18)
CO2 = [(M - 2P) x 0.79] + [2P x 0.35]
where:
CO2 = carbon dioxide estimate, ppm as CO2
M = total (methyl orange) alkalinity, ppm as CaCO3
P = phenolphthalein alkalinity, ppm as CaCO3
EXAMPLE 3-5:
a) Measured P = 2 ppm, M = 60 ppm
b) Bicarbonate CO2 contribution [60 - (2 x 2)] x 0.79 = 44.2
60
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