Modern Pumping Today February 2025 - 19

they operate. Moreover, salinity in the coastal areas
makes the surrounding air very humid and corrosive and
wreaks havoc on pump efficiency and can cause damage,
downtime, or failure, " says Greg Gedney, industry
expansion manager at Greene Tweed. Backed by his
two-decades long experience in pumping technologies,
he adds, " The abrasive and corrosive nature of seawater,
brackish water, concentrated brine, and treatment
chemicals can damage pump components made of
traditional material, requiring more frequent replacement. "
According to Dave Noblin, product manager of SEC
Platform at Greene Tweed says, " By upgrading to
components made of corrosion and abrasion-resistant
composite materials, such as WR®
and AR®
, pump
engineers can significantly lower the life cycle cost of
pump operations by extending service life, reducing
pump overhaul costs, and maintenance expenses. " This
strategic selection of pump components, he explains, " will
not just extend the lifespan of pump systems, but also
pave the way for a more sustainable future. "
HOW GREENE TWEED HELPED
Power plants, one of the largest water users globally, face
a formidable challenge: the corrosive and abrasive threat
of saltwater. From cooling systems to hydraulic operations,
their critical pump components need to withstand the
harsh seawater and brackish water environments.
Consider Duke Energy, the operators of the North
Carolina-based Brunswick nuclear power plant. Back
in 2015, they were looking to replace eight Circulating
Water Pumps (CWP) being used to pump high volumes
of seawater. Duke Energy engineers needed to upgrade
the bearing from cutlass rubber because of delamination
issues. " Presence of saltwater containing salt, slit, and
sand can damage the mating shaft, its sleeve, and the
rubber cutlass bearings in circulating water pumps, "
says Gedney, who was working with the pump's
original equipment manufacturer to support Brunswick
nuclear plant.
An external flush provided to each of the composite
bearing locations in the pump would trigger an alarm
when the flush dropped below five gallons per minute of
flow to the bearings. The low flush alarm was set to two
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minutes of low conditions prior to tripping the power to
the pumps, causing significant problems. Gedney explains
why: " This meant that if the bearing flush flow wasn't
restored within two minutes, the pump would shut down
and disrupt the process. Additionally, frequent starting
and stopping of the pump can be highly detrimental to
its performance. "
To reduce the disruptions, the nuclear plant's
engineering team requested the pump's manufacturer
to extend the low flow / flush alarm from two minutes to
fifteen minutes on the new pumps. The increased alarm
to trip time on the new pumps meant that the bearings in
the pump needed to survive a minimum of fifteen minutes
under low-flow conditions.
The pump manufacturer reached out to Greene Tweed
and our engineers proposed AR-HT bearings, executing
a bearing test program to validate AR-HT composite
bearings in an environment tougher than requested -
totally dry conditions. Tests were performed with AR-HT
bearings and Stellite 12 shaft sleeves on the rotor, chosen
due to their compatibility to saltwater and their surface
hardness characteristics.
SURPASSING EXPECTATIONS
Greene Tweed's AR-HT bearings surpassed expectations,
by resisting wear and maintaining running clearances,
for longer than 105 minutes-compared to the original
request of just fifteen minutes-in dry run conditions
without any lubrication. The pumps upgraded with AR-HT
bearings and Stellite 12 shaft sleeves, installed in 2016,
have not required any significant maintenance since
then. According to Duke Engineering, vibration levels are
consistently low and smooth running. Since the bearing
system is no longer the maintenance limiting factor of the
CWPs, the preventive maintenance frequency is likely to
extend beyond the planned fifteen years, " says Gedney.
Encouraged by the results, Duke Brunswick plant
engineers upgraded their service water pumps to the
same combination: AR-HT bearings and Stellite 12
sleeves. " Our bearings delivered once again and will now
be used in the upcoming replacement of the circulating
water ocean discharge pumps, " he adds.
Greene Tweed designs and manufactures components,
materials, and solutions that perform in the harshest
environments. We engineer for conditions where equipment
failure is not an option. Our products are made for extreme
temperatures, pressure, chemical corrosion, and mechanical
wear. With over 200 engineers in labs throughout North
America, Europe, and Asia serving a variety of industries,
we work with you to create a customized solution tailored
to your critical operations' requirements. For more
information, visit www.gtweed.com.
FEBRUARY 2025 | 19
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Modern Pumping Today February 2025

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