11 NACE INTERNATIONAL: VOL. 56, NO. 3 MATERIALS PERFORMANCE MARCH 2017
THE BLOG
Continued on page 13
More on Chlorine
Dioxide Corrosion
Editor:
I am writing in regards to the Decem-
ber 2016 MP article, "The Effect of Chlo-
rine Dioxide on Corrosion in Seawater."
Unfortunately, the article does not pro-
vide enough detail for it to be useful. It
should have addressed very relevant
questions such as:
1. How was the chlorine dioxide (ClO
2
)
generated? Many methods produce
some free Cl
2
, which create a much
more corrosive environment than
ClO
2
alone.
2. What was the mode of treatment?
at is, were they feeding continu-
ously or intermittently? is is very
relevant. Research has shown that
while low-level continuous treat-
ment is better for chlorine, short-
term, intermittent, higher dosage
applications of ClO
2
(~1 ppm) is more
effective at controlling biofilm.
3. e paper completely misses the
mark on the graph shown. e graph
is from a paper by Ingols and
Ridenour in 1948. ey treated a
river water in the Northeastern
United States that was contami-
nated with either ammonia or
organic nitrogen. e plot shown for
chlorine is characteristic of ammo-
nia-contaminated water; it shows
typical breakpoint behavior. is
was not mentioned and the graph
will be completely different for
waters without either ammonia or
organic nitrogen compound
contamination.
4. Was the cooling loop once-through
(which the paper seems to suggest)
or was it an open recirculating
cooling tower? If it was once-
through, the chlorite level would
only be in the ppm range, and so the
corrosion rate for this concentration
of chlorite would be expected to be
very low. Again, insufficient
information.
5. Finally, how was the ClO
2
tested for?
Was chlorite tested for? How often?
e article is not clear on either
point. A graph of data points for
measured ClO
2
and chlorite residu-
als would provide a lot of informa-
tion. Were there periods of time
where ClO
2
was not fed? at is,
could biofilm growth have occurred
during the test?
6. Was bacterial testing done? What
were these results?
In short, there is not enough infor -
mation in this article to allow a ClO
2
-
knowledgeable person to make any kind
of judgment as to what the real effect of
adding ClO
2
to seawater has.