POWER January 2020 - 32

WATER
Water Chemistry:
Power Plant Life and Death
Power plants that use steam to generate electricity need water. Without it, they can't
do their job. But water and steam are complicated, much as is blood in our veins
and arteries. So, water chemistry is a big, complex and important job in steamelectric
power plants.
Kennedy Maize
W
ater is the lifeblood of all steam
electric power plants-coal,
combined cycle gas, or nuclear
fueled. Literally.
On Dec. 9, 1986, a rupture in an elbow
in the system that condenses cooling
water at the Surry nuclear power plant
(Figure 1) near Williamsburg, Virginia,
killed four workers and cost tens of millions
of dollars in lost revenues and repair
costs. The cause, according to the
Electric Power Research Institute (EPRI),
was corrosion in a bend in the pipe from
a feedwater pump. The pressurized water
flashed to steam, scalding the workers
and taking the plant out of service.
Reuters reported at the time, " A similar
accident at Surry about three years ago
killed one worker and injured another. "
The Importance of Water Chemistry
" Lifeblood? I agree 100%, " Daniel Wells,
program manager of EPRI's nuclear sector
water chemistry program, told POWER.
The power industry's chief research
and development group has long had an
active program for water chemistry in
steam-electric power plants. The major
generating technologies have common
water concerns. Wells, a nuclear guru,
said, " In general, water chemistry is one
of the main ways we maintain material
lifetime " in steam plants.
Alex Filar of Maryland-based Fossil
Consulting Services Inc. also buys the
" lifeblood " metaphor. In a company blog
two years ago, he wrote, " At the heart of
nearly ever[y] power plant are a boiler, a
turbine, and associated condensate and
feedwater systems. The water and steam
coursing through them is the lifeblood
of the electrical generating process. As
such, it is of the utmost importance that
the water/steam is properly monitored
and treated. Poor water chemistry control
can lead to deleterious effects on equipment
uptime, plant budgets, and most
importantly, personnel safety. "
The task for plant managers and operators
is to control impurities and other
characteristics in the water that transforms
heat into steam and steam into
electric power. Impurities can cause corrosion
and cracking. Corrosion caused by
oxidizing metal surfaces can release rust
into the water stream and lead to deposits
elsewhere in the plant's innards.
That can also lead to deposits in the
boiler, said Wells, reducing heat transfer
and a slowing flow rate of water through
the system. That means a less efficient
plant and, as seen at the Surry plant,
threats to worker safety.
Filar observed, " To better prevent
these negative effects, water chemistry
control has undergone substantial changes
over the past 30 years. These changes
have been the result of a commitment to
research and technological development
by the chemistry community. However,
it is the power plant operator who is responsible
for ensuring that these changes
are implemented at their plant. And with
an aging workforce in the industry, it is
now more important than ever that the
next generation of operators understand
proper water chemistry control. "
EPRI's Wells said operators need to
concentrate on two major objectives:
corrosion cracking, which can lead to
pipe failure, and general corrosion, which
can reduce heat transfer, lessen flow
rate, and cause material degradation.
It's Chemistry and Metallurgy
Writing in POWER a few years ago (see
" Feedwater Chemistry Meets Stainless
Steel, Copper, and Iron, " in the
March 2015 issue), David Daniels, water
chemistry specialist at M&M Engineering
Associates Inc. of Leander, Texas,
described three major metallurgies and
their water chemistry challenges. " Alloys
found in the condensate and feedwater
systems of power plants include carbon
steel for piping, pumps, and in some
cases heat exchangers. Many systems
still have some copper-based alloys from
admiralty brass and copper-nickel (Cu-Ni)
alloys all the way to 400 Series Monel,
primarily as feedwater heater tubes. "
Stainless steel alloys generally avoid
the common corrosion mechanisms that
afflict carbon steel and copper alloys.
That's because stainless " is protected
by a tight adherent chromium oxide layer
that forms on the surface, " Daniels wrote.
" There is the tendency to think that
1. Surry Units 1 and 2 are three-loop Westinghouse pressurized water reactors that began operation
in December 1972 and May 1973, respectively. In October 2018, Dominion Energy filed
an application to extend the operating licenses for the two units through 2052 and 2053-when
they will be 80 years old. Source: U.S. Nuclear Regulatory Commission
32
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stainless steel is the perfect alloy to
replace copper-alloy feedwater tubes, "
said Daniels. But the Achilles' heel of
stainless is that chlorides and corrosive
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POWER January 2020

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