a high degree of accuracy.
These metal samples are put into a
system and exposed to the water in the
system for an extended duration. After
a period of time, the metal samples are
removed and sent in for analysis where
they are first cleaned of debris and
The difference in the metal mass (i.e.
metal loss) and the length of exposure
(in days) are used to calculate the corrosion rates. In this study, corrosion
coupons were employed in addition to
the corrator to monitor the cumulative
corrosion rates over a 45-60 day exposure period. The results are summarized in Table 3.
The results were better than anticipated and the primary objective of
eliminating phosphorus from the cooling tower chemical treatment program
In addition, the zero phosphorus treatment program provided a significant reduction in the corrosion rates. The corrosion rates dropped from an average 4
mpy to an average 1. 3 mpy. The results
signify a significant shift in paradigm in
the water treatment industry.
The norm used to be for facilities to
have to settle for compromised results
or additional water use when using alternate chemicals that didn’t contain
Now, industry is able to meet low
P concentrations in their discharges
while still protecting their critical assets.
The client wanted to maintain the
same water efficiency (i.e. not reduce the
cycles of concentration) which yielded a
Index (LSI) of approximately 2. 25.
This LSI represents
a relatively high scaling potential and the
heat transfer surfaces were monitored
closely as well. During the course of
the entire trial there was no observed
accumulation of scale that would impede the heat transfer efficiencies. Table 2 lists the pertinent cooling tower
values during the trial.
After the zero phosphorus program
was implemented the corrosion rates
improved drastically within the first 5
hours of application. The on-line corrator corrosion rates for the mild steel
(Figure 2 on page 43) shows the significant improvement during the implementation phase.
The corrosion rate in mils per year
(mpy) is shown to fall from greater
than 2. 5 mpy to less than 0.5 mpy.
Corrators are good tools to measure
trends and instantaneous relative cor-
rosion rates. Corrosion coupons are
an alternative method to monitor the
same parameter. Corrosion coupons
are samples of pertinent metal (i.e. mild
steel or copper) that are pre-weighed to
Traditional water treatment pro-
grams were being utilized in the treat-
ment of the cooling towers. The pro-
gram for the first cooling tower (Tower
#1) utilized an all-organic program
with an azole supplement due to the
copper metallurgy contained within
Power plants traditionally do not contain copper metallurgies so the concerns
associated with minimizing copper corrosion are not as pertinent and will not
be discussed in this article. The other
cooling tower system (Tower #2) did not
have an azole supplement.
The results obtained from the first
chemical program (All-Organic #1) were
satisfactory, but U.S. Water tried an alternative all-organic program (All-Organic
#2) to try and improve the results.
The corrosion rates actually in-
creased slightly from the 1st program to
the 2nd program in Cooling Tower #2.
Figure 1 (on page 42) shows the corro-
sion rates in the cooling tower systems
for the various programs:
Due to the discharge regulations, the
client needed to find a viable chemical
treatment alternative. With the help of
U.S. Water, a new program was identi-
fied (PhosZero TM) and the program was
implemented at the plant. In order to
ensure proper system protection, the
corrosion rates were carefully moni-
tored using corrosion coupons as well
as an on-line corrator.
pH --- 8.59 8.58
Conductivity µmhos/cm 2,117 2,299
“M” Alkalinity ppm as CaCO3 422 446
Chloride ppm 123 315
Calcium ppm as CaCO3 774 570
Magnessium ppm as CaCO3 665 500
Silica ppm as SiO2 37. 3 36. 8
Sulfate ppm as SO4 732 678
Cooling Tower Parameters TABLE 2
Source: Data & Pictures Courtesy of U.S. Water Services
Zero P 1.661
Tower #2 0.702
Zero P 1.465
Zero Phosphorus Corrosion Coupon Results TABLE 3