Nuclear Plant Journal, May-June 2016 NuclearPlantJournal.com
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manufactured to the same pattern and
drawing numbers. Upon closer inspection,
however, the OD and vane underfiling
geometry of the spare impeller were found
to deviate from the OEM’s specifications.
Expected loss of hydraulic performance
due to this deviation was calculated and
brought to the customer’s attention, with
suggested additional improvements. For
the purpose of minimizing repair time
while still being able to meet the specified
requirements, hydraulic calculations
were run upfront. The results of the
calculations pointed out that there would
be ~4.3 % relative increase in a developed
head for the spare impeller. Though the
estimated head was slightly above the
maximum allowable limit, the test results
were expected to meet the requirements
by making up for any degradation due
to the casing which had been in service
for many years. Additionally, it was
recommended to smoothly round the
impeller vane’s leading edges to improve
suction capability. The results of this
analysis gave the customer confidence
in the expected performance results
and enabled them to conclude against
modification of the impeller’s hydraulic
geometry.
In addition, Hydro reviewed the
impeller’s overall outer sizes along with
the casing’s inner sizes and a diminished
axial float (gap) was identified between
the impeller shroud’s outer walls and
the casing’s inner wall, an area of
primary concern. When the top half of
the casing was lowered down, there was
an obstruction. On the application of
bluing, it became clear that the casing
wall was hitting the impeller shroud on
the outboard end. With closer review of
the parts and drawing, Hydro’s engineers
identified that the overall exit width,
including the shroud thickness of the
spare impeller, was larger by ~0.145" as
compared to the drawing, thus forcing
the loss of the axial float (gap) by the
same amount. Service-center engineers
recommended machining the shroud
faces axially near the impeller OD, to
relatively increase the overall float (gap)
but to be within the drawing requirements.
Engineering evaluations pointed out
that this recommended modification
would not diminish mechanical strength,
axial thrust or the pump’s hydraulic
performance. This enabled the customer
618-244-6000
NEW QUALIFICATIONS TO SUPPORT
Power Uprates
•
License Extension
•
Changes in Postulated Conditions
INNOVATIVE SOLUTIONS TO
OBSOLESCENCE ISSUES
COMMERCIAL GRADE QUALIFICATION AND DEDICATION SINCE 1979
E X P E D I T E D QUA L I F I C AT I ON
D E D I C AT I ON & P E R F O RMAN C E T E S T I NG
Nutherm
International, Inc.
to approve the recommendation of
machining the shroud faces.
HydroAire completed the repairs
to the rotor and casing, following our
engineering evaluation. These alterations
were made while retaining other hydraulic
sizes, in order to avoid any adverse
influences of the hydraulic parameters.
Hydraulic Performance
Test
The service center’s in-house
performance test lab was kept on
standby with the preliminary test
layout throughout the repair process.
Customer Supplied Spare – Larger Diameter Impeller.
