Nuclear Plant Journal, July-August 2016 NuclearPlantJournal.com
43
Custom-
Built Pump
Breakthrough
Reliability and Greater Efficiency through Design
Innovation
By Faisal Salman, Hydro, Inc.
Faisal Salman
Faisal Salman serves as director of
nuclear services at HydroAire, a division
of the Hydro Group of companies.
Salman has
been involved in
aftermarket pump
refurbishment and
troubleshooting
for 28 years. He is
a graduate of the
University of Illinois
with a Bachelor
of Science degree
in mechanical
engineering.
Custom building a unique pump can
provide an innovative solution to a pump
problem. Hydro, Inc. recently had the op-
portunity to design and build such a pump
for one of our customers. This challenging
case represents an opportunity to tackle
a persistent performance issue by using
new technologies to engineer, design, and
manufacture a new pump custom-tailored
for our client’s particular application and
to do so in an aggressive time frame (for
a nuclear-code pump) of only 16 months.
Additionally, the application required ex-
otic metallurgy (AL-
6XN) that presented
additional complex-
ity. The option to de-
sign a custom pump
provided the plant
with significantly in-
creased efficiency and
improved
reliabil-
ity while ameliorat-
ing the existing issues
with a safety-related
device.
Overview of
problem:
A nuclear plant
had 10 identical
pumps installed in its service-water
systems. Formidable power-supply and
cooling-media constraints, design issues,
and poor-quality manufacturing had
caused numerous operational problems.
The motor was overloading on a regular
basis due to inefficiency of the existing
pumps. The plant was having a hard time
juggling a HP limit—the existing driver
could not be changed, which limited
maximum allowable BHP.
Further, highly corrosive, full-
strength seawater from the estuary
area of a blackwater river served as the
cooling media. This brackish, tannic
water caused the bowl assembly to
experience high pitting and crevice
corrosion beyond repair. (The plant
had upgraded the column assembly to
super austenitic material in the 1990s,
but the bowl assembly remained in the
original material.) In addition, packing-
box leakage was causing corrosion to
the foundation where the pumps were
located.
The decision to build a
custom-designed pump:
Hydro had been contracted five
times to complete repairs on these pumps
between August 2009 and October 2014.
During the course of these repairs, Hydro
came to a number of conclusions which
eventually led to the recommendation to
consider custom-designing a pump for
this specific application.
A key factor with respect to
recommending a custom-built pump
came from test results performed
following each repair. The performance
curves did not match each other, nor
did they match the OEM curve. This
suggested that the original impellers
(which were not modified in any way
during the repairs) differed, most likely
due to casting variations. For example,
in 2011, Hydro repaired one of the bowl
assemblies with spare OEM parts. When
performance-tested, the results failed to
meet requirements, with considerable
differences recorded especially on the
total developed head. [Fig. A]
Additional assessments of the
existing original pump performance
revealed other problems. Station records
showed relatively high thrust-bearing
temperatures implying relatively higher
axial down thrust. Inferior hydraulic
performance was found to be due to non-
optimum hydraulic design, non-uniform
impeller vane tips and poor surface
quality (from inferior casting quality),
as well as a problem with the hydraulic
passages from the suction bell inlet to
the discharge bowl exit (there was not a
smooth transition for the flow).
After thorough analysis, Hydro was
able to design a pump that addressed
all of the problems. Hydraulic-design
modifications were engineered to meet
stringent duty requirements with high
efficiency. Wear-ring geometry was
optimized. High-quality casting processes
ensured dimensional accuracy that was
modeled and then implemented. High-
