POWER September 2010 - 59

WATER TREATMENT
cases where the cation conductivity is stable,
such an increase would be seen as unusual
and warrant further investigation. In cases
where makeup water or organic treatment
chemical additions vary, it may be more difficult
to determine if the increase in cation
conductivity is from a condenser tube leak or
some other cause.
Although an increase in sodium at the
condensate pump discharge may signal an
analyzer problem, and an increase in cation
conductivity could have a number of possible
sources, if there were an increase in
both, then the probability of a condenser
tube leak is very high. This is why both cation
conductivity and sodium analyzers are
must-have analyzers on both a steam sample
(reheat or main steam) and at the condensate
pump discharge.
Given the levels of sodium and cation
conductivity in this example, the change in
chemistry suggests a leak of approximately
100 ml/minute-a leak in a single tube smaller
than the period at the end of this sentence.
It would be very difficult to find such a leak
with anything but a helium leak detector.
However small the leak, its effect is substantial.
Chlorides at 5 ppb in the feedwater would
concentrate considerably in the boiler water and
would likely increase to well above 1 ppm chloride
in most utility boilers that normally keep
the continuous blowdown line essentially closed
during operation. A level of even 1 ppm chloride
would be intolerable for a unit operating
on any boiler water treatment except, perhaps,
a high-level phosphate treatment. Even with the
blowdown open and continuous high levels of
phosphate feed, the potential for underdeposit
corrosion, such as hydrogen damage forming in
the boiler, is substantial.
The Electric Power Resesarch Institute
(EPRI) Chemistry Guidelines (on the EPRI
website) provide charts showing the acceptable
levels of chloride and sulfate for various operating
pressures. When a condenser tube leak is
suspected, analytical methods must be in place
to analyze chloride and sulfate levels in the boiler
frequently. The boiler must come off line if
the established limits cannot be maintained not
only for pH, but also for chloride and sulfate.
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Make Your Decision
With proper analytical monitoring techniques,
such as a low-level sodium analyzer
at the condensate pump discharge and a
continuous chloride analyzer on the boiler
water, you may be able to detect very small
condenser tube leaks in time to let you run
to the weekend and avoid a forced outage. If
so, operating the boiler to minimize attemperation
flow will minimize contamination
of the steam and hence minimize the chance
for later boiler and steam turbine problems.
However, if the chloride and sulfate levels
in the steam or boiler quickly rise (when the
condenser leak is large), the unit must immediately
come off line to prevent substantial
and costly damage to the unit. In either case,
good analytical instruments that are properly
placed in the boiler and cooling water systems
are vital to making informed decisions.
One final thought: Remember to drain and
flush the hotwell and drain the boiler when
you come down for a condenser tube leak in
order to remove any accumulated contamination.
Be especially vigilant during the subsequent
start-up to ensure that the right tube was
plugged and that the chemistry is quickly returning
to normal. In any case of severe contamination,
a chemical cleaning of the boiler
should be scheduled for the next outage.
In Part II, we explore the different mechanisms
that cause condenser tube leaks. ■
-David G. Daniels (david_daniels@
mmengineering.com) is a principal of
M&M Engineering and a POWER
contributing editor.
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POWER September 2010

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