BWROG-TP-09-005, Inspection of Motor Operated Valve Limitorque AC Motors with Magnesium Rotors
- Rev 0 - March 5, 2009, https://www.nrc.gov/docs/ML0914/ML091480655.pdf
text
ENCLOSURE 2
Inspection of Motor Operated Valve Limitorque AC Motors with
(BWR OWNERS' GROUP NON-PROPRIETARY)
[BWR]
OWNkERSi' GROUP
BWROG Non-Proprietary Information - Limited Distribution BWROG-TP-09-005
Revision 0
March 05, 2009
Inspection of Motor
Operated Valve Umitorque
AC Motors with
A Technical Product of the BWR Owners Group
Valve Technical Resolution Group
Prepared by: Paul Waterloo
Schulz Electric Company
Date: 02/23/09
Approved by:
Endorsed by:
Ted Neckowicz (Exelon)
Chairman - VTRG
Pat McQuillian
Date: 02/24/09
Date: 02/24/09
NOTICE
This guideline contains information for inspection of Reliance AC MOV motors
with magnesium rotors, based on industry operating experience and the
collective engineering expertise of the BWROG Valve Technical Resolution
Group. It is the decision of each member utility to implement any or all of these
guidelines.
Any use of this guideline or the information contained herein by anyone other
than members of the BWR Owners Group Valve Technical Resolution Group
(112) is unauthorized. With regard to any unauthorized use, the BWR Owners
Group makes no warranty, either express or implied, as to the accuracy,
completeness, or usefulness of this guideline or the information, and assumes no
liability with respect to its use.
Participating Utilities
The Valve Technical Resolution Group is a non-generic committee and all
BWROG members participated, at the time of this report the BWROG
membership included:
Utility (Members)
Constellation - NMP Exelon (P/L)
Energy Northwest - Columbia FirstEnergy - Perry
Entergy - Fitzpatrick NPPD - Cooper
Entergy - Pilgrim NMC - Monticello
Entergy -,VY PPL - Susquehanna
Entergy - RB/GG PSEG - Hope Creek
Exelon (Clinton) Progress Energy - Brunswick
Exelon (OC) SNC - Hatch
Exelon (D/Q/L) TVA - Browns Ferry
Table of Contents
1. Executive Summary .................................................................................... 1
2 . Intro d u ctio n ................................................................................................ . . 1
3. How to Determine if a Motor has a Magnesium Rotor ...................................... 1
3.1 Electrical Apparatus Motors ......................................................................... 1
3.2 Reliance Electric Motors ......................................................................... 2
3.2.1 48 and 56 Frame Motors .................................................................. 2
3.2.2 180 and Larger Frame Motors ........................................................ 2
3.2.3 Limitorque Electric Motor Corporate Date Code .............................. 3
4. Degradation Mechanisms ............................................................................. 4
4.1 Galvanic Corrosion .................................................................................. 5
4.2 General Corrosion ................................................................................... 6
4.3 Thermally Induced Stress ....................................................................... 6
5. Failure Mechanishms of Magnesium Rotors ............................................... 8
5.1 Rotor Cooling Fin Interference with Stator W inding ................................ 8
5.2 Magnesium End Ring/Rotor Bar Failure ............................................... 10
6. Motor Inspection Priority ............................................................................. 12
7. Required Equipment for Inspection ............................................................. 16
7.1 Assembled Motors ................................................................................ 16
7.1.1 Video and Image Capture ............................................................. 16
7.1.2 Borescope/Videoscope Minimum Requirements ............................ 17
7.1.3 Borescope Catalog Information ...................................................... 19
7.1.4 Borescope/Videoscope Cost ......................................................... 19
7.2 Disassembled Motors ........................................................................... 19
8. Visual and Borescope Inspection Procedure ............................................. 20
8.1 Type LR Motors .................................................................................... 20
8.2 Installed "T" Drains ............................................................................... 20
8.3 Internal Motor Components .................................................................. 23
8.4 Acceptance Criteria ............................................................................. 28
9. New Motor Inspection Critera .................................................................... 35
10. Maintaining Environmental and Seismic Qualification ............................... 37
1 1 . P h o to s ..................................................................................................... . . 4 2
12 . A ppend ices ............................................ I .............................................. . . 4 2
13 . R eferences ............................................................................................ . . 4 3
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Inspection of MOV Magnesium Rotors
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1. EXECUTIVE SUMMARY
Recent US Nuclear industry motor operated valve (MOV) failures due to
magnesium motor rotor degradation warrant additional action to better monitor
and evaluate magnesium rotors installed in Reliance MOV AC motor
applications. Internal inspection of motor rotors by use of a borescope or via
motor disassembly is recommended. Using the standardized acceptance and
inspection schedule prioritization criteria described herein, motors will be
scheduled, inspected and evaluated as Failed (Unacceptable), Degraded or
Acceptable. This recommended approach is especially paramount for high-risk
applications of motors that are not accessible during normal plant operations.
This document provides recommendations for inspecting susceptible MOV
motors for BWROG members and its affiliates.
2. INTRODUCTION
MOV operators supplied with Reliance AC motors with magnesium rotors are
susceptible to catastrophic failure of the motor rotor and stator preventing the
actuator from being able to perform its intended safety function. Motors supplied
with aluminum rotors are not subject to the same failure mechanisms. This
document was produced as a users guide to better understand rotor failure,
methods of inspection, inspection criteria, examples of satisfactory and
unsatisfactory conditions, and MOV programmatic implementation.
3. HOW TO DETERMINE IF A MOTOR HAS A MAGNESIUM ROTOR
3.1 Electric Apparatus, Paramount and Peerless Motors
Some Limitorque operators were supplied with electric motors manufactured by
Electric Apparatus, Paramount and Peerless. It has been confirmed by
Limitorque that motors supplied by Electric Apparatus, Paramount and Peerless
do not have magnesium rotors, they were supplied with aluminum rotors.
Therefore, all such motors are not susceptible to the failure mechanisms covered
in this report.
See Reference 13.7, Limitorque Technical Updated 08-01 concerning rotor
material of Electric Apparatus, Paramount and Peerless motors.
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3.2 Reliance Electric Motors
Baldor Electric Motor Company purchased Reliance Electric and now produces
and supports the Reliance electric motor line. For the purpose of this document,
all MOV motors will be referred to as manufactured by Reliance, which is now
Baldor/Reliance.
Limitorque operators supplied with Reliance motors can have magnesium rotors.
This is dependent upon frame size; start torque; and speed of the motor.
Limitorque has provided the industry with Technical Update 08-01 (Reference
13.7) which provides a general classification for Reliance motors supplied with
3.2.1 48 and 56 Frame Motors
All 48 and 56 frame size motors supplied by Reliance were constructed with
aluminum alloy rotors.
Frame Size Speed (RPM) Start Torque Rotor
(lb-ft) Construction
48 All All Aluminum Alloy
56 All All Aluminum Alloy
3.2.2 180 and Larger Frame Motors
Frame sizes 180 and larger were all constructed with magnesium alloy rotors
prior to the early 1990's. Certain frame sizes have been converted to aluminum
alloy rotors since that time. The following tables provide a general guideline on
motors that have been converted to aluminum alloy rotors. The recommended
method of determining rotor material is to contact Limitorque directly with the
serial number/nameplate information.
Motors Converted to Aluminum Alloy Rotors in Early 1990's
Frame Size Speed (RPM) Start Torque Rotor
(lb-ft) Construction
180 1800 40 Aluminum Alloy
180 3600 40 Aluminum Alloy
184 1800 60 Aluminum Alloy
210 1800 100 Aluminum Alloy
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Inspection of MOV Magnesium Rotors
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Motors Presently Available with Aluminum Alloy Rotors *
Frame Size Speed (RPM) Start Torque Rotor
(lb-ft) Construction
210 3600 60 Aluminum Alloy
210 1800 80 Aluminum Alloy
210 3600 80 Aluminum Alloy
256 1800 150 Aluminum Alloy
256 1800 200 Aluminum Alloy
• Notes
1. If an aluminum alloy rotor motor is supplied, the speed/torque/current
curve could be different from the original magnesium rotor motor. This
should be evaluated in the utility MOV program.
2. The list of large frame motors available in aluminum is subject to
change. Contact Limitorque directly for the latest information.
3.2.3 Reliance Electric Motor Corporate Date Code
Appendix 1 is the Reliance Electric Motor Corporate Date Code which
determines the month and year of manufacture of the electric motor. This chart
should be used in conjunction with the nameplate information on the motor.
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Inspection of MOV Magnesium Rotors
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Figure 1 - Month and year of manufacture can be determined by the last two alpha characters in
the Identification Number field. This motor has a data code of HC, which corresponds to a
manufacturing date of August 2000 as shown on Appendix 1,
Reliance Electric Motor Corporate Date Code.
3.2.4 If uncertain as to the rotor type of a Reliance supplied motor, contact the
Limitorque Corporation with the motor serial number and nameplate
information to determine if the motor was supplied with a magnesium alloy
or aluminum alloy rotor. The results of rotor type should be documented in
the utilities' MOV program.
4. DEGRADATION MECHANISMS
The causal factors (degradation mechanisms) leading to magnesium rotor failure
have been documented by many sources including NRC Information Notice (IN) 2006-06, Failure of Magnesium Rotors in Motor-Operated Valve Actuators
(Reference 13.1) and IEEE Transactions on Energy Conversion, Vol. 3, No. 1,
"An Investigation of Magnesium Rotors in Motor Operated Valve Actuators",
March 1988 (Reference 13.4). The following is a summary of causes from these
sources.
The typical magnesium rotor is made of stacked, steel punched core plates with
AM100A magnesium alloy (approximately 90% magnesium, 10% aluminum,
0.1% manganese) components-the conductor bars, end rings, and cooling fan
blades-cast to complete the rotor. While magnesium provides higher torque, as
compared to aluminum, through its higher resistivity, this relatively brittle cast
alloy is susceptible to shrinkage cracking and gas porosity. Specifically,
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magnesium rotors are susceptible to three main degradation mechanisms:
galvanic corrosion, general corrosion, and thermally induced stress.
4.1 Galvanic Corrosion
Following manufacture, the electrical potential difference between the cast
magnesium and the steel core is 1.9 volts creating the conditions for galvanic
corrosion, with the most vulnerable area being the interface between the steel
core and the magnesium end ring. Galvanic corrosion will occur at this interface
under humid/moist conditions. Most manufacturers alleviate this by protecting the
magnesium end rings with a paint and/or lacquer coating. Though the rotor might
be initially protected, even the smallest scratch or chip in this exterior coating will
cause localized, accelerated corrosion in the form of magnesium hydroxide
(MgOH) powder. The formation of MgOH powder leads to rotor cracks that add to
the existing problems of shrinkage cracking, gas porosity, and MgOH volume
difference. Motor overheating events (typically due to locked rotor conditions)
accelerate this coating degradation. A propagating crack at the interface between
the stacked core and the end ring causes a high resistance connection with the
end ring, which in turn causes a high current density (due to current
redistribution) on the opposite side of the rotor. This increased current density
increases the temperature on that side of the rotor resulting in thermal stress. At
the steel-magnesium interface, the higher temperature may melt the magnesium
into small beads. These thermally-stressed rotor areas and the melted
magnesium beads then provide new opportunities for coating degradation and
cracking resulting in new areas of high resistance between the stacked core and
end ring and new areas of the rotor with a higher current density. This cycle of
events can then repeat around the rotor.
Figure 2 - Onset of galvanic corrosion between magnesium end ring and end lamination.
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Inspection of MOV Magnesium Rotors
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4.2 General Corrosion
The second major degradation mechanism affecting magnesium rotors is general
corrosion. Many actuator motors for safety related MOVs are located in high
humidity plant areas. Consequently, some moisture intrusion into the motors is
expected via motor T-Drains and the unsealed motor lead passageway.
Moisture in contact with magnesium leads to the formation of MgOH and
magnesium oxide (MgO 2). The white MgOH powder can form a light haze on the
inside of the motor without impacting its operation. However, MgOH and MgO 2
can form corrosion between core plates (from the magnesium conductor bars)
and at the interface between the stacked core and the end ring, causing high
resistance points and the high current density phenomena stated above and
even further cracking. The rate of general corrosion increases with higher
humidity.
Figure 3 - General corrosion on magnesium end ring.
4.3 Thermally Induced Stress
The third major degradation mechanism affecting magnesium rotors is thermally
induced stress which reveals itself in several different ways. First, because
galvanic corrosion is thermally catalyzed, the corrosion rate increases with
temperature, with a significant increase in the corrosion rate occurring at
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temperatures above approximately 93 C (200 F). The rate of galvanic corrosion
increases when the motor is located in a higher temperature environment, as well
as during general motor high-current conditions and/or within the high current
density regions mentioned earlier. Secondly, magnesium has twice the thermal
expansion coefficient of steel. This produces uneven axial and radial forces
across the rotor causing further cracks in the magnesium and its paint and/or
lacquer coating. Excessive motor cycling and inadvertent motor stalls are the
most likely cause of thermally induced stress. For example, some rotors reach
700'F (371' C) in 15 seconds, and temperatures of 700'F to 8500 F (3710 C to
4540 C) cause a significant loss of magnesium yield strength.
Figure 4 - Thermally induced stress failure of 150 lb-ft magnesium rotor. This motor was
automatically energized by the control system at locked rotor conditions for approximately 0.4
seconds followed by six seconds of not being energized. This continued for approximately 90
minutes. The valve was bound in place so the motor rotor did not turn (operated at locked rotor
condition). After approximately 90 minutes, the motor stator winding failed and a ground fault
indication tripped the motor control center supply breaker.
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Figure 5 - 150 lb-ft magnesium rotor after removal from stator frame. Note the heavy heat
damage on the magnesium rotor end rings as compared to that apparent on the center
body of the rotor.
5. FAILURE MECHANISMS OF MAGNESIUM ROTORS
Magnesium rotors have two failure mechanisms. The motor rotor can fail due to
deflection of the rotor cooling fins insofar that the fins contact the stator windings
and cause an electrical failure of the motor. The second failure mechanism is the
failure of the magnesium end ring and/or rotor bars by overheating. This causes
beads of molten magnesium to form and become foreign material in the motor
internals which can interfere with the rotor causing seizure and/or reduce the
available torque of the motor to a fraction of nameplate torque.
5.1 Rotor Cooling Fin Interference with Stator Winding
When the interface between the magnesium rotor and the end lamination
corrodes due to galvanic corrosion, corrosion products build up between these
two components. The corrosion product causes the magnesium end ring to
deflect radially outwards. This deflection can be so great that it causes the
cooling fins of the rotor to come in contact with the stationary stator windings.
After the rotor comes in contact with the stator, it will cause mechanical damage
to the stator and a turn-to-turn or turn-to-ground electrical failure occurs.
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Inspection of MOV Magnesium Rotors
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Figure 6 - Onset of magnesium end ring separating from rotor end lamination. The cooling fin has
deflected outwards towards the stator winding but has not yet come in contact with the stator
winding. This motor would not meet borescope inspection acceptance criteria.
Figure 7 - Magnesium rotor with cooling fins deflected due to the growth of corrosion products
between the end lamination and magnesium end ring. The rotor cooling fin came in contact with
the stator winding and caused the motor to fail.
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Figure 8 - Motor stator winding failure due to motor rotor cooling fins contacting the stator winding
during operation. The cooling fins were deflected due to corrosion products between the end
lamination and magnesium end ring.
5.2 Magnesium End Ring/Rotor Bar Failure
The second type of degradation of a magnesium rotor motor is when the rotor
catastrophically fails due to the magnesium end ring and rotor bars melting. This
can cause the rotor to no longer produce nameplate torque due to the failure of
the rotor bars and shorting rings. It may also cause loose magnesium foreign
material to enter the air gap between the rotor and stator. This can cause the
rotor to abruptly seize in the stator bore.
In the case of this type of failure, there is a possibility that the degraded rotor
condition could be evaluated by non-intrusive testing of the MOV at the motor
control center. One diagnostic technique involves a standard fast Fourier
transform of the reactive motor power data in the running load region. The
difference in magnitude between the line frequency and the pole pass modulation
frequency can be used to determine the likelihood of motor rotor bar
degradation'.
1Motor Operated Valve User Group File 95S-P25, Magnesium Motor Testing Case Study, J
Arnold (ComEd), M Delzingaro (Liberty Technology), July 1995
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This condition can normally be associated with a locked rotor condition or severe
excessive stroking of the operator. If the motor rotor has some level of galvanic
corrosion in place, the safe stall time of the motor is most likely reduced making
the motor more susceptible to this failure.
Figure 9 - Catastrophic failure of magnesium rotor where the magnesium casting melted
during a locked rotor condition.
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6. MOTOR INSPECTION PRIORITY
Visual inspection via borescope or disassembly is required to properly inspect
the condition of a magnesium rotor to determine its acceptability of continued
use. Other non-intrusive methods of inspection alone have not been proven to
determine the acceptability of magnesium rotors susceptible to degradation
factors discussed in section 5 of this document.
"I</br></br>2 OE 27927, Magnesium rotor failure on main feedwater block valve (Crystal River 3)</br></br>[[BWROG" contains a listed "[" character as part of the property label and has therefore been classified as invalid., Rev. 0
Inspection of MOV Magnesium Rotors
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7. REQUIRED EQUIPMENT FOR INSPECTION
7.1 Assembled Motors
To inspect assembled motors in the field installed on an operator or for motors in
onsite storage, a videoscope/borescope is required to inspect the motor
internals. The motor internals will be inspected via the access provided by
removing the installed "T" drains or pipe plugs.
7.1.1 Video and Image Capture
Borescopes that will be used for inspection of the motor internals that can
capture images are normally videoscopes, i.e. they capture videos (.avi, .mpg
format) during the inspection. Some borescopes have the ability to capture both
video and still images (.bmp, .jpg). Image quality is not compromised if using
video or image formats. Each borescope system has a built in video/image
quality built into it. Systems with a VGA (640 x 480 pixels or better) should be
considered.
WVGA
//
i I ;
Figure 10 - Display Type vs. Pixel Size. When procuring a videoscope/borescope,
one with VGA display and recording ability should be considered.
Borescopes with a QVGA resolution (320 x 240) are not recommended.
If a videoscope is used, captured videos can be converted into still images by
transferring the file to a PC, and playing the video back with proper software. The
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video can be paused and a still shot captured. When taking video of motor
internals, if an area of concern is found, the videoscope should be paused while
videoing the area. This will result is a high-quality still image without distortion
from camera movement.
7.1.2 Borescope/Videoscope Minimum Requirements
The borescope/videoscope should have the following minimum requirements:
- Articulating Probe
- Probe length of 1-2 meters
- 6 or 8 mm probe size (6 mm is preferred)
- 90 degree side view tip
- Light source for probe
- VGA viewing screen
- Portable
- Battery operated for field use
- Battery operated light source for field use
Figure 11 - ForeEyesTM 2020 videoscope with 6mm articulating probe. A compact unit such as
this is recommended for field inspections. The image on the left shows the operator moving the
articulating four way probe by turning the control wheel. Image on the right is possible positions of
a four way video probe.
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There are many manufacturers of borescope equipment on the market today. A
small, easy to handle, portable unit that can easily download videos/images to a
PC should be considered. A unit with a large amount of memory is an advantage
when taking videos.
An articulating probe is required for inspection. Once the probe is inside the
motor, the operator maneuvers it with a thumbwheel control while viewing the
screen. The video/images can be downloaded via memory module to a PC for
viewing and storage. If the device is only a videoscope such as the
ForeEyesX2TM 2020 unit, in order to look at still pictures, the video must be
downloaded to a PC. It can then be viewed with viewing software and the video
stopped to capture a specific frame. Borescope/videoscope images are not
normally larger than 640 x 480 pixels (VGA). Borescope/videoscopes with 320 x
240 pixels (QVGA) should not be considered for this application due to the low
resolution.
Figure 12 - iTool videoscope. It consists of the computer, the light source
(cylinder on left hand side) and four way articulating probe.
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Figure 13 - GE XL GoTM Video Probe
Another example of a handheld videoscope. Dimensions are 3.75"x 5.25"x 13.5"
7.1.3 Borescope Catalog Information
See Reference 13.9 for Danatronics, iTool and GE videoscope catalog
information. This information is not meant to be a recommendation, but general
information and specification for a portable unit.
7.1.4 Borescope/Videoscope Cost
The cost for a high-quality borescope/videoscope with required accessories can
range from approximately $15,000 to as much as $40,000.
7.2 Disassembled Motors
For disassembled motors, a borescope could be required if the bearings/bearing
brackets are not removed from the rotor shaft; however, a digital camera is most
likely the only tool required. The images should be saved for later comparison
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against future inspections of the same motor rotor and for comparison against
other motor rotors.
8. VISUAL AND BORESCOPE INSPECTION PROCEDURE
8.1 Type LR Motors
Type LR motors cannot be inspected via borescope (type can be found on the
nameplate of the motor under "insulation type"). This is due to an internal shield
installed between the bearing bracket and motor rotor. These motors require
disassembly to be inspected.
Figure 14 - Type LR motor rotor. Note the large shield inboard of the bearing.
This prevents field inspection of the rotor via borescope.
8.2 Installed "T" Drains
Motors shall be inspected in-situ by use of a borescope for motors that have "T"
drains installed. Removal of the "T" drains will allow inspection of the
rotor/internals of the motor.
NOTE ON "T" DRAINS:
Limitorque installed "T" drains on some MOV motors during the environmental
qualification process to allow for pressure equalization of the motor. In these
cases, "T" drains must be installed to maintain the qualification of the
actuator/motor.3
3 Limitorque Valve Actuator Qualification for Nuclear Power Station Service Report B0058,
Section 3.2.3 and 4.1.2
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It should be noted that some plants and/or end use applications do not require
the use of "T" drains and utilize pipe plugs instead. In these cases, "T" drains are
not required to maintain the environmental qualification status of the motor.
The number, location, and arrangement of motor "T" drains should be maintained
in accordance with the plant EQ Program requirements.
Figure 15- "T" drain plugs supplied with environmentally qualified MOV motors from Limitorque.
These plugs must be installed to maintain environmental qualification of the motor. They shall be
oriented at the lowest point of the motor, one on each bearing bracket.
Figure 16 - Label attached to Limitorque motors. For non environmentally qualified applications,
the "T" drain plugs are not required to be installed.
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Remove the "T" drain fittings from both the drive end and opposite drive end
bearing brackets.
Figure 17 - "T" drain inspection port locations. There are other locations clocked on the bearing
brackets that have NPT pipe plugs inserted. Use the "T" drain and other pipe plug locations
for borescope inspection.
Insert the borescope/videoscope in the "T" drain and pipe plug locations to
inspect the motor rotor. If the motor is not attached to an actuator, the shaft can
be easily spun to aid inspection of the rotor. If performing the inspection in the
field, the borescope will have to be snaked around the rotor through multiple
inspection ports to completely inspect the rotor because the shaft will not turn.
Using the different ports and articulating the borescope probe allows for complete
inspection. Capture images or video of the motor rotor internals. If using a
videoscope, pause at locations to capture the video, especially areas of concern.
This will create high quality still images at a later time due to lack of distortion of
the image from video probe movement.
Inspection must be completed on both the drive end and opposite drive end of
the motor. Rotor degradation can occur on one end of the rotor as viewed by
visual or borescope inspection, but appear normal on the other end.
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Figure 18- Borescope probe inserted for inspection through "T" drain opening
8.3 Internal Motor Components
The following are internal motor components that will be visible during the
borescope inspection. For more pictures of borescope/videoscope inspections,
see HTML format on supplied disc.
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Figure 19 - Rotor Assembly. Note where balancing of the rotor was accomplished at 3 o'clock
position. The balance nubs were removed and the cooling fins were ground down to remove
weight from this area of the rotor. After balancing, the rotor fins were not coated. Also note the
lack of coating on the magnesium in general. Note black discoloration at the 10 o'clock position.
This could be corrosion products or lack of coating.
Figure 20 - Rotor still installed in motor stator. The magnesium hydroxide powder can be seen at
the O.D. of the rotor and at the balance nub at the I o'clock position. The magnesium end ring is
overheated and discolored from the original insulating paint color of light green. The formation of
magnesium hydroxide powder in this example is most likely due to thermally induced stress.
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Figure 21 - Outside diameter of motor rotor removed from the motor stator. Note the magnesium
hydroxide powder at the interface of the end lamination and the magnesium end ring. This is
caused by galvanic corrosion across the interface. Note the overall color of the magnesium end
ring; it is darkened in color, which can be seen better in the next image.
Figure 22 - Magnesium rotor with indications of thermally induced stress at the end rings on both
sides. This can be seen by the brown discoloration of the end rings, which were originally the light
green color. Magnesium hydroxide powder can be seen on the right hand end lamination to end
ring interface. The left side had a small rub between the rotor laminations and stator, causing the
paint to be removed where the stripe can be seen.
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Figure 23 - Stator Frame Assembly
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Figure 24 - Drive End Bearing Bracket with space heaters installed. Space heaters are installed in
the drive end only. Bearing cap not shown installed.
The motor rotor should be inspected via borescope at the junction of the
outboard-most electrical steel rotor lamination where it comes in contact with the
magnesium end ring. This is the most common place for galvanic corrosion to
occur, which forms magnesium hydroxide (MgOH) powder. Once the MgOH
powder is present, it is relatively easy to see.
The interface of the magnesium end ring to lamination is of utmost importance.
This interface is where galvanic corrosion occurs and the corrosion products are
deposited. Once deposited, these corrosion products push the magnesium end
ring, which skews the rotor fan blades relative to the rotor body. The area
between the magnesium end ring and the end lamination must be inspected for a
gap, corrosion products or paint deterioration.
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Figure 25 - Unpainted magnesium rotor after casting and quenching process.
It should be noted that it is normal to have some separation of the magnesium
end ring relative to the end lamination. According to the motor manufacturer, the
rotor manufacturing process calls for quenching after the magnesium casting
process to assist in the surface separation of these materials to improve motor
efficiency. The gap is the result of this process and alone is not cause for motor
rejection during inspection. This gap is normally 0.030" but can vary from this
average value. The image above shows a type end ring separation between the
magnesium end ring and end lamination.
8.4 Acceptance Criteria
The following items should be inspected during either an in-situ or disassembled
test. The motor shall be free of any defects listed in Table 2 below (Failure
Criteria) or Table 3 (Degradation Criteria).
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Inspection of MOV Magnesium Rotors
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Table 2 - Motor Inspection Failure Criteria
Figure Item Identified
Yes No
Any observed gap or separation between the rotor end
6, 25, 32 lamination and the magnesium end ring with evidence of
corrosion at or near the gap interface.
Any outward spreading or radial misalignment of any cooling
6, 7, 28 fin. This would normally be found in conjunction with the item
above.
Black corrosion product build-up between the rotor end
36 lamination and the magnesium end ring.
Black corrosion product build-up at outside diameter of rotor
21 at magnesium end ring.
Indication of thermally induced stress. Obvious darkening or
22 discoloration of the magnesium end ring adjacent to the rotor
end lamination.
Balance nubs or outside edges of the cooling fins are
26 corroded away. This should not be confused with the factory
removal of balance nubs or grinding of the cooling fins during
the rotor balance process.
The magnesium end ring is broken or has missing sections.
27, 29 Pieces of the magnesium end ring or cooling fins are found
detached within the motor housing.
Globular or molten metallic deposits appear anywhere on the
30 surface of the magnesium end ring and/or cooling fins.
Any cracking in the magnesium end ring or the cooling fins,
31 particularly where the cooling fins join the magnesium end
ring.
Any evidence of contact between the rotor cooling fins and
8 the stator windings.
Excessive corrosion or bubbling of the magnesium end ring
26 or cooling fins.
Note: For Group A Motors (Section 6.3.1) found to have one or more of the above indications
shall be considered failed and the motor should be replaced or reconditioned. For Group B
motors (Section 6.3.2) found to have one or more of the above indications shall be dispositioned
by a formal engineering evaluation or replaced or reconditioned prior to return to service.
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Inspection of MOV Magnesium Rotors
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Table 3 - Motor Inspection Degradation Criteria
Figure Item Identified
Yes No
34 Slight blistering of the protective coating of the magnesium
end ring or the cooling fins.
2, 3, 33 Minor pockets of corrosion on the magnesium end ring
and/or the cooling fins.
2, 33 Minor galvanic corrosion at the interface of the magnesium
end ring and end lamination.
Note: For Group A Motors (Section 6.3.1) found to have one or more of the above indications
shall be considered failed and the motor should be replaced or reconditioned. For Group B
Motors (Section 6.3.2) found to have one or more of the above indications should be considered
degraded and scheduled for another inspection or replacement or reconditioning within the
greater of the end of the next fuel cycle or 24 months.
Figure 26 - Example of excessive corrosion on rotor cooling fins.
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Inspection of MOV Magnesium Rotors
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Figure 27 - Rotor with cooling fan/magnesium end ring detached.
Figure 28 - Excessive corrosion of magnesium end ring combined with the cooling fins being
deflected outwards from the body of the rotor.
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Inspection of MOV Magnesium Rotors
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Figure 29 - Catastrophic failure of magnesium end ring.
Figure 30 - Failed magnesium rotor. Note angularity of rotor fins relative to shaft and globs of
molten magnesium. Note this is shown with the bearing bracket removed in a shop environment.
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Inspection of MOV Magnesium Rotors
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Figure 31 - Deflected cooling fins on left hand side with cracking evident. Right hand side cooling
fins also demonstrate cracking.
Figure 32 - Acceptable separation and paint cracking between magnesium end ring and end
lamination with no corrosion present.
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Inspection of MOV Magnesium Rotors
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Figure 33 - Minor galvanic corrosion at the interference of the
magnesium end ring and end lamination.
Figure 34 - Slight blistering onset of corrosion of the magnesium end ring/cooling fins coating.
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Inspection of MOV Magnesium Rotors
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9. NEW MOTOR INSPECTION CRITERA
New motors should be inspected prior to placing them in service. This can be
completed by borescope/videoscope inspection or by disassembly and
inspection. All criteria for in-situ or disassembled motor inspection are applicable
for new motors. The motor rotor should be in excellent condition with a proper
coating. If the coating is compromised, consideration should be given to motor
disassembly and rotor recoating.
The motor rotor can be cleaned by glass bead blasting and coating with Ranvar
B-5-346 or BT-7455A air dry primer. This is the coating used by the motor OEM
to coat magnesium rotors. Two coats should be used to achieve a proper coating
with no visible magnesium showing.
Reference 13.10 is the technical data sheet for Ranvar B-5-346A and BT-7455A
air dry primer.
Figure 35 - Properly coated rotor at magnesium end ring to lamination interface.
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Inspection of MOV Magnesium Rotors
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Figure 36 - Magnesium rotor with black corrosion product build-up between the rotor end
lamination and the magnesium end ring. NOTE: one cooling fin has broken off the end ring.
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Inspection of MOV Magnesium Rotors
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10. MAINTAINING ENVIRONMENTAL AND SEISMIC QUALIFICATION
Limitorque actuators and motors can be supplied as environmentally qualified
(EQ). The environmental qualification status must be maintained if the motor is
disassembled for inspection or other corrective action. The actuators and motors
were qualified by Limitorque Corporation to the requirements of IEEE382-1977;
IEEE 323-1974 and IEEE 344-1975 as delineated in the following qualification
reports 4:
- Report B0058 - Limitorque Valve Actuator Qualification for
Nuclear Power Station Service, Dated 1/11/1980,
- Project 600376A Report F-C3441 - BWR Containment Qualification,
Dated 5/13/1976.
- Project Report 600456 - PWR Containment Qualification, Dated
12/09/1975 (M)
- Project 600461 Report B0003 - Outside Containment Qualification, Dated
6/02/1976.
- Project 600426 Report B0009 - DC Actuator Qualification, Dated
4/30/1976
- Project 600508 Report B0027 - Superheat Temperature Test, Dated
8/31/1978
- Project Report B0212 - LR Type Motor PWR Qualification, Dated
4/10/1985 (M)
(M) - These tests included a magnesium rotor motor
Reference 13.6 specifically discusses magnesium rotor aspects with respect
to Limitorque Equipment Qualification. Below is an excerpt from Reference
13.6.
"Magnesium rotors only exist on certain Reliance AC motors. Both aluminum
and magnesium rotor motors have been tested as tabulated below. Since
magnesium rotor motors acceptably passed the 600456 and B0212 steam
test conditions, Limitorque has concluded that rotor materials do not affect the
level of motor qualification (FN4). Limitorque certifies the performance of
magnesium rotor motors to all referenced tests."
4 There have been other entities that have environmentally qualified Limitorque MOV Actuators
and Motors. For purposes of this section, only Limitorque EQ reports are listed.
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Inspection of MOV Magnesium Rotors
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Magnesium Rotor Motor Data:
EQ Test Rpt Rotor Material
(1)600456: Magnesium
(2) B0212: Aluminum (connected to actuator)
Magnesium (operated in test chamber)
(3) All Others: Aluminum
FN4 - A magnesium rotor motor as part of the B0212 test program was
successfully tested to the transient portion of the same profile reported in
the B0212 test report. The results are not published in the B0212 test
report, however, this information is on file and available for audit at
A review of the subject reports was performed to determine the potential impact
of disassembly upon magnesium rotor motors qualified for EQ applications.
Based upon the review of the subject reports, it was concluded that there are two
subcomponents that could potentially impact the EQ status of the motor by the
disassembly, inspection and reassembly process. This assumes that the motor is
disassembled and reassembled properly and the bearings are not removed from
the shaft. The two components identified are the motors shaft seal and the
bearing bracket o-rings. It is also important to understand the function and safety
classification of these subcomponents.
There were no subcomponents identified during the review that could potentially
affect the seismic qualification status of the motor.
10.1 Design Function of Shaft Seals.and Bearing Bracket O-rings
The shaft seal and bearing bracket o-rings are manufactured from an
elastomeric material. The design function of the shaft seal and bearing
bracket o-rings is to prevent external environmental contaminants (e.g.
dirt, dust and grease) from entering the motor internals. This is considered
good engineering practice in motor.design.
The shaft seal is subject to shaft rotational forces. Upon. disassembly, the
seal should be inspected for possible wear and/or loss of elasticity which
could result in failure of the shaft seal to perform its design function. If the
seal condition is suspect, then the seal should be replaced prior to
reassembly.
The bearing bracket o-rings are installed between the bearing bracket and
motor stator and are loaded in compression. Upon disassembly, the orings
should be inspected for possible compression set and/or loss of
elasticity. If the o-ring condition is suspect, then the o-rings should be
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Inspection of MOV Magnesium Rotors
Page 39 of 43
replaced prior to reassembly. It is generally considered good maintenance
practice to replace o-rings that are installed in compression applications
whenever equipment is disassembled.
10.2 Material of Construction and Environmental Considerations
The shaft seal and bearing bracket o-rings are manufactured from a
fluoroelastomer commonly known as viton. All elastomers are subject to
some degradation at elevated temperatures and when exposed to
radiation. Generally, volume change, increase in hardness and
compression set are characteristics that are most affected. The shaft seal
and bearing bracket o-rings could be exposed to high temperature and
radiation environments due to the motors inherent end use application.
The amount of degradation also increases with exposure duration and
increase in environmental stressors. Consideration of these factors should
be taken into account when evaluating possible replacement of these
components during disassembly and inspection of motor magnesium
rotors.
10.3 Safety Function and EQ Status of Shaft Seals and
Bearing Bracket O-rings
Limitorque Report B0058, Sec. 3.2., "Seals" states, "Limitorque actuators
for nuclear plant applications are designed to permit them to survive
normal and accident conditions without depending on absolute sealing. In
fact, the ambient is not absolutely restricted from entering the actuator.
The seals are of no importance for qualification and, therefore, required no
consideration for the qualification." Limitorque Report B0058, Sec. 4.1.2,
"Design Philosophy", further states, "In all cases, the philosophy of using
an actuator that did not require complete integrity of sealing was used. In
fact, containment units include "T" drains to permit them to breathe."
"Limitorque adopted this philosophy to minimize maintenance man-hours
in a containment chamber which would be necessary to replace seals on a
periodic schedule and the extremely difficult chore of assuring the actuator
doesn't leak when exposed to an external pressure which would actually
be the responsibility of the utility once the actuator shipped from the
manufacturer's plant."
"The second reason for adopting this philosophy is to provide additional
confidence in Limitorque valve actuators by eliminating the concern that
any one of the several seals or gaskets might start leaking during plant
operation which in all probability would assure failure of a "sealed"
actuator in event of a DBE."
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Inspection of MOV Magnesium Rotors
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Based upon the above, it could be concluded that the shaft seal and
bearing bracket o-rings are considered non-safety related and therefore
not considered EQ. However, some end users may consider the shaft seal
and end bracket o-rings to be safety related and/or environmentally
qualified. It is ultimately the end users responsibility to determine the
safety classification and EQ status of the shaft seal and end bracket
o-rings in accordance with each plant's individual requirements.
It is therefore also incumbent upon each end user to effectively maintain
the EQ status of their respective magnesium rotor motors. If the end user
maintains that the shaft seals and bearing bracket o-rings are considered
EQ, then the replacement shaft seal and o-rings must be evaluated for the
environmental parameters of the host component end use application. If
the shaft seal and bearing bracket are considered non-safety related, then
it recommended that the replacement seal and o-ring be manufactured
from fluoroelastomer material with the same dimensions as the original.
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Inspection of MOV Magnesium Rotors
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Bearing Bracket, opposite drive end (ODE). Both drive end (DE) and opposite drive end bearing
brackets have a o-ring installed that sits in a machined fit in the bearing bracket. This creates a
seal with stator frame.
Shaft lip seal. Shown from the inside of the pulley end motor bearing bracket on the left (bearing
and bearing cap removed) and from the outside of the drive end bearing bracket on the right.
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Inspection of MOV Magnesium Rotors
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11. PHOTOS
Photos of motor rotor inspections has been compiled in HTML format and can be
found on the CD ROM with this document. It must be viewed with a browser such
as Windows Internet Explorer or Mozillia Firefox. The following examples are
included:
- Borescope Inspection Pictures and Notes
- Shop Inspection Pictures and Notes
- Motor and Rotor Failures
12. APPENDICES
12.1 Limitorque Electric Motor Corporate Date Code
12.2 Motor Disassembly and Reassembly Procedure
12.3 Motor Inspection Failure and Degradation Criteria Tables
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Inspection of MOV Magnesium Rotors
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13. REFERENCES
13.1 NRC Information Notice (IN) 2006-26: Failure of Magnesium Rotors in
Motor-Operated Valve Actuators
13.2 NRC Information Notice (IN) 1986-02: Failure of Valve Operator Motor
during Environmental Qualification Testing
13.3 NRC Information Notice (IN) 2008-20: Failure of Motor Operated Valve
Actuator Motors with Magnesium Alloy Rotors
13.4 IEEE Transaction on Energy Conversions, Vol. 3, No. 1, March 1988, An
Investigation of Magnesium Rotors in Motor Operated Valve Actuators.
13.6 Nuclear Utility Group on Equipment Qualification - Clarification of
Information to the Environmental Qualification of Limitorque Motorized
Valve Operators, August 1989. (Limitorque Approved September 1989)
13.7 Limitorque Technical Update 08-01, Reliance Motors/Magnesium Rotors
13.8 AREA NP Document 54-9078869-001, Criteria for the Videoscope
Inspection of New Safety-Related Baldor AC Motors Used with Flowserve
MOV Actuators
13.9 Borescope Equipment Catalog Sheets
13.10 Technical Data Sheet Ranvar B-5-346 (M-32250 NH) and
Ranvar BT-7455A Air Dry Primer
13.11 Flowserve Acceptance Letter of Document with Exceptions
Appendix 1 Limitorque Electric Motor Corporate Date Code
Limitorque Electric Motor Corporate Date Code
Year Jan Feb *Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1971 AW BW CW DW EW FW GW HW JW KW LW MW
1972 AX BX CX DX EX FX GX HX JX KX LX MX
1973 AY BY CY DY EY FY GY HY JY KY LY MY
1974 AZ BZ CZ DZ EZ FZ GZ HZ JZ KZ L MZ
1975 NA PA QA RA SA TA UA VA WA XA YA ZA
1976 NB PB QB RB SB TB UB VB WB XB YB ZB
1977 NC PC QC RC SC TC UC VC WC XC YC ZC
1978 ND PD QD RD SD TD UD VD WD XD YD ZD
1979 NE PE QE RE SE TE UE VE WE XE YE ZE
1980 NF PF QF RF SF TF UF VF WF XF YF ZF
1981 NG PG QG RG SG TG UG VG WG XG YG ZG
1982 NH PH QH RH SH TH UH VH WH XH YH ZH
1983 NJ PJ QJ RJ SJ TJ UJ VJ WJ XJ YJ ZJ
1984 NK PK QK RK SK TK UK VK WK XK YK ZK
1985 NL PL QL RL SL TL UL VL WL XL YL ZL
1986 NM PM QM RM SM TM UM VM WM XM YM ZM
1987 NN PN QN RN SN TN UN VN WN XN YN ZN
1988 NP PP QP RP SP TP UP VP WP XP YP ZP
1989 NQ PQ QQ RQ SQ TQ UQ VQ WQ XQ YQ ZQ
1990 NR PR QR RR SR TR UR VR WR XR YR ZR
1991 NS PS QS RS SS TS US VS WS XS YS ZS
1992 NT PT QT RT ST TT UT VT WT XT YT ZT
1993 NU PU QU RU SU TU UU VU WU XU YU ZU
1994 NW PW QW RW SW TW UW VW WW XW YW ZW
1995 NX PX QX RX SX TX UX VX WX XX YX ZX
1996 NY PY QY RY SY TY UY VY WY XY YY ZY
1997 NZ PZ QZ RZ SZ TZ UZ VZ WZ XZ YZ ZZ
1998 AA BA CA DA EA FA GA HA JA KA LA MA
1999 AB BB CB DB EB FB GB HB JB KB LB MB
2000 AC BC CC DC EC FC GC HC JC KC LC MC 2001 AD BD CD DD ED FD GD HD JD KD LD MD
2002 AE BE CE DE EE FE GE HE JE KE LE ME
2003 AF BF CF DF EF FF GF HF JF KF LF MF
2004 AG BG CG DG EG FG GG HG JG KG LG MG
2005 AH BH CH DH EH FH GH HH JH KH LH MH
2006 AJ BJ CJ DJ EJ JF GJ HJ JJ KJ LJ MJ
2007 AK BK CK DK EK FK GK HK JK KK LK MK
2008 AL BL CL DL EL FL GL HL JL KL LL ML
2009 AM BM CM DM EM FM GM HM JM KM LM MM
2010 AN BN CN DN EN FN GN HN JN KN LN MN
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Inspection of MOV Magnesium Rotors, Appendix 2
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Appendix 2
Disassembly and Re-Assembly Procedure
Adding Inspection Ports
The following procedure should be used to disassemble motors removed from their
operators for rotor inspection. The end user should determine which portions of this
procedure are applicable to their application. This procedure assumes the motor will be
disassembled, reassembled and tested. If only performing disassembly for inspection,
certain steps may be omitted. This procedure also includes provisions for installing
borescope inspection ports in the bearing brackets.
This procedure does not cover:
- Repair of shaft to bearing ID fit
- Repair of bearing OD to bearing bracket fit
- Any other repairs to the motor
Tools Required
- Various wrenches
- Mallet to tap bearing brackets
- Bearing puller to pull bearings
- Induction bearing heater to install new bearings
Precautions and Limitations
rotor across the stator windings at the end turn area. This can nick the windings
and require the stator to be rewound.
• Means for tagging all removed parts shall be established and followed.
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1. DISASSEMBLY PROCEDURE
1.1 Preliminary Electrical and Mechanical Tests 1.1.1 Measure the stator insulation resistance. Record results. Acceptance
Criteria: > 5 M Ohms
1.1.2 Measure the winding resistance of all three phases. Record results.
Acceptance Criteria: All phases within 5% of each other
1.1.3 Measure the polarization index. Record results.
Acceptance Criteria: >2 < 6
1.1.4 Measure the shaft extension runout. Record results.
Acceptance Criteria: < 0.002"
1.1.5 Measure the shaft endplay. Record results. Acceptance Criteria: None, this
is for information only
1.2 Disassembly
1.2.1 Match-mark all interfacing components before disassembly to ensure proper
reassembly. Sketches should be made of item interfaces that may not be
obvious to the mechanic assembling the unit. If the unit is already matchmarked,
record the marks on the job's paperwork if different from conventional
marking system. Take pictures of match-marks if in a complex configuration or if
difficult to discern pattern.
Punch Mark Convention
Single Shaft Extension I DE: 2 marks I ODE: 3 marks
Note: Some Limitorque motors have lead-exit sealant material (generically
referred to as "Chico," which is in fact a specific product of the Crouse-
Hinds Corporation) which is used to seal the lead exit at the pulley end
bearing bracket. If lead-exit sealant material is found, the drive end bearing
bracket cannot be removed without possible permanent damage to the lead
wire. However, the motorcan still be disassembled, but the drive end
bearing bracket must be left in place. Therefore, only the opposite drive end
can be inspected.
1.2.2 With the motor on its side, remove the opposite drive end (ODE) bearing bracket
bolts (4). Remove the ODE bearing cap bolts (3). NOTE: Not all MOV motors
have bearing caps installed. If bearing caps are not installed, no bearing cap
bolts will be present. Remove the ODE bearing bracket. Tapping it with a mallet
will most likely be required to break the seal with between the bearing bracket
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Inspection of MOV Magnesium Rotors, Appendix 2
Page 3 of 16
and stator frame. Once the seal is broken, use a prying device as required to
remove the bearing bracket. If a prying device is used, work it from side to side to
ensure the bearing bracket does not cock in the stator frame. The ODE bearing
and bearing cap will remain on the shaft.
Bolt Holes
Bearing Cap and Bolts It
Opposite drive end (ODE) bearing bracket and bearing cap/bolts. The bearing bracket
captures the bearing in the bearing bracket.
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Inspection of MOV Magnesium Rotors, Appendix 2
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ODE Bearing Bracket
with Bearing Cap
Installed
1.2.3 Remove the drive end bearing bracket bolts (3). Remove DE bearing bracket.
This is completed in the same fashion as the ODE bearing bracket. When
removing the DE bracket, feed the heater and stator leads through the opening in
the bearing bracket.
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Inspection of MOV Magnesium Rotors, Appendix 2
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DE Bearing Bracket as viewed from the inside of the motor.
Bearing cap not installed.
1.2.4 Once both bearing brackets are removed from the stator frame, remove the rotor
by CAREFULLY pulling it out of the stator bore. CAUTION: Do not drag the rotor
body over the stator windings otherwise damage to the stator windings could
occur.
1.2.5 The rotor can now be inspected.
1.3 LR Motor Components
LR motor type can be determined by nameplate information. In the "Ins. Type"
block, the letters "LR" will be written. These motors have internal shields on both the
DE and ODE end.
1.3.1 ODE Components. The ODE has a shield attached to the bearing cap with
spacers. If the rotor is to be pulled out from the DE side, the shield must be
removed before the rotor can be pulled through the stator bore. If removing the
rotor from the ODE side, the rotor can be removed and the shield then removed
from the bearing cap. The ODE bearing WILL REQUIRE removal from the shaft in
order to remove the shield.
Type LR motor rotor/shield/bearinga ssembly. These motors have a large shield inboard
of the bearing that precludes inspection of the motor rotor via borescope.
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ODE Bearing Cap. This cap is similar to type RH insulation motors but have three additional
tapped holes on the stator side of the cap to capture the shield.
There are normally spacers between the cap and the shield as shown above.
Shield attached to bearing cap with three screws.
Spacers are located between the bearing cap and the shield.
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Inspection of MOV Magnesium Rotors, Appendix 2
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Bearing bracket installed on shaft (clearance fit). The bearing is then fit to the shaft and the bearing
bracket installed and the cap/shield assembly is captured via (3) bolts.
ODE bearing bracket/shield assembly on motor shaft. ODE bearing NOT shown installed.
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Inspection of MOV Magnesium Rotors, Appendix 2
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1.3.2 DE Components. The DE has a shield mounted into the DE bearing bracket. It is
held in place with 3 bolts. The bearing cap is separate from the shield. The rotor
can be removed from the stator bore by removing it from the ODE end.
DE Bearing Bracket
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Inspection of MOV Magnesium Rotors, Appendix 2
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DE bearing bracket with shield installed. Bolts are shown NOT screwed all the way in.
DE bearing bracket with shield installed and bearing cap in place.
Shield bolts are shown NOT screwed all the way in.
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Inspection of MOV Magnesium Rotors, Appendix 2
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2. BEARING FITS
2.1 The bearings do not have to be removed from the shaft in order to inspect the rotor.
If they are to be replaced, they will need to be removed from the shaft by use of a
puller, and fits checked.
Drive end of failed MOV motor. The bearing and bearing cap are
installed on the shaft. A puller must be used to remove the bearing.
2.2 If the bearings are to be removed and replaced, the fit of the shaft to inside
diameter (ID) and bearing bracket housing to bearing outside diameter (OD) must
be checked for a proper fit. This procedure does not cover corrective action for
out-of-tolerance fits.
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2.3 Bearing Fits
The following table should be used for bearing fit acceptance criteria. Once the bearing
size is determined, consult a bearing catalog to determine acceptance criteria for
bearing fits.
Shaft to Bearing Inside Diameter Fit
Bearing ID (mm) Bearing Fit/Tolerance
Symbol
< 18 j5
(18)-100 k5
Bearing Outside Diameter to Housing Fit
Bearing OD (mm) Bearing Fit/Tolerance
Symbol
All H6
3. ASSEMBLY
3.1 If bearings were removed from the shaft, install the bearing caps (if motor is
equipped with bearing caps) on the shaft and install bearings on the shaft. Ensure
the bearings meet the fit criteria above prior to installation.
3.2 To capture the bearing caps, use a longer length bearing cap bolts to capture the
bearing cap after the bearing bracket is installed. This allows the bearing cap to be
drawn into place. Once the bolt bottoms out, remove one of the longer bolts, and
install the original bearing cap bolt. Repeat with other bolts.
3.3 Repeat for other bearing bracket.
3.4 Perform Final Electrical and Mechanical Tests 3.4.1 Measure the stator insulation resistance. Record results.
3.4.2 Measure the winding resistance of all three phases. Record results.
3.4.3 Measure the polarization index. Record results.
3.4.4 Measure the shaft extension runout. Record results.
3.4.5 Measure the shaft endplay. Record results.
Perform no load operational test and record: Voltage, current, speed and vibration
levels.
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Inspection of MOV Magnesium Rotors, Appendix 2
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4. INSTALLATION OF BORESCOPE INSPECTION PORTS
Some Limitorque motors were supplied without "T" drains/drain plugs installed on the
bearing brackets. The following procedure should be used as a general guideline for
drilling and tapping new holes for pipe plug fittings which can be used for borescope
inspection ports.
Motors that were supplied with pipe plugs have 3/8"-18 threads per inch (TPI) NPT pipe
plugs installed. These same pipe plugs will be retrofitted to existing motors without pipe
plugs.
NOTE: This is not applicable to type LR motors due to the internal baffles installed in
the motors. Type LR motors can only be inspected via disassembly.
Tools and Materials Required
" Drill Press
" Clamping Device for Bearing Bracket
- 3/8"-18 TPI NPT Pipe Tap
- 3/8"-18 TPI NPT Pipe Plugs (up to 7 per motor)
" 37/64" Drill Bit
- Center Punch
- Thread Cutting Oil
It should be noted that pipe sizes do not refer to any physical dimensions. For example,
a 3/8" NPT pipe thread has an outside diameter of 0.675". Each thread size has a
defined number of threads per inch (TPI). The 3/8" NPT pipe thread has 18 threads per
inch. Both the TPI and OD of the thread are required for positive identification of thread
size because several sizes have the same TPI.
Nominal Dimensions for 3/8" Pipe Fitting
Dimension Value
A: Male Thread O.D. 0.675"
B: Female Thread I.D. 0.675"
C: Nominal Engagement for Tight Joint 0.410
Threads Per Inch 18
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Inspection of MOV Magnesium Rotors, Appendix 2
Page 13 of 16
Precaution: The following procedure and hole locations are based on bearing brackets
that were supplied with pipe plug installed at the factory. The user must determine the
suitability of location of pipe plug holes for motors that were not supplied with "T"
drains/pipe plugs. Use caution when determining drilling locations to ensure that there
will not be interference with other components or degradation of bearing bracket
strength due to hole location.
4.1 Disassemble the motor and clean the DE and ODE bearing brackets of any dirt or
grease. Remove space heaters from DE bearing bracket, if installed.
4.2 Determine location for bearing bracket pipe plugs.
4.2.1 Drive End Bearing Bracket
The DE bearing bracket will have no more than three holes drilled. These holes
should be 180 degrees across from the motor lead entrance area (1 hole) and (2)
holes 90 degrees relative to the lead entrance area. Once the hole location is
determined, mark location with a center punch.
BWROG-TP-09-005, Rev. 0
Inspection of MOV Magnesium Rotors, Appendix 2
Page 14 of 16
4.2.2 Opposite Drive End Bearing Bracket
The ODE bearing bracket will have no more than (4) holes drilled at 90 degree
intervals. These holes should be located between the bearing bracket-to-stator
frame hole locations. Once the hole location is determined, mark location with a
center punch.
ODE Bearing Bracket. Pipe plug locations equally spaced between
bearing bracket-to-stator frame bolting locations.
BWROG-TP-09-005, Rev. 0
Inspection of MOV Magnesium Rotors, Appendix 2
Page 15 of 16
Locate the hole for the pipe plug in the proper location radially and axially in the bearing
bracket casting. Consideration must be taken when determining
drilling location for both the inside and outside of the casting.
4.3 Drill and Tap the Pipe Plug Holes
4.3.1 Mount the bearing bracket in a suitable clamping device so it can be held at the
drill press. Ensure the bearing bracket is securely mounted to the drill press to
prevent movement during the drill process.
4.3.2 Using a 37/64" drill bit, drill through the bearing bracket at the marked location.
4.3.3 Before unclamping the bearing bracket from the clamping device, tap the drilled
hole all the way through the opening using thread cutting oil while tapping. If the
BWROG-TP-09-005, Rev. 0
Inspection of MOV Magnesium Rotors, Appendix 2
Page 16 of 16
material is too deep to tap completely through the drilled hole, the hole must be
tapped to a minimum depth of 0.600". The nominal length of engagement of the
plug in the hole must be 0.410" to ensure a tight joint.
4.3.4 Unclamp the bearing bracket and set up for next hole until all holes are drilled and
tapped.
4.4 Clean the bearing bracket of all metal chips/filings ensuring there is no foreign
material left in the bracket or bearing housing.
4.5 Install pipe plugs in new holes snug tight.
4.6 Reinstall heaters on DE bearing bracket, if previously installed.
4.7 Reassemble and test the motor per instructions above.
BWROG-TP-09-005, Rev. 0
Inspection of MOV Magnesium Rotors, Appendix 3
Page I of 2
Appendix 3
Motor Inspection Failure and Degradation Criteria Tables
The motor inspection failure and degradation criteria tables are presented in Microsoft
Word format below for ease of use for plant personnel to cut and paste into station
procedures.
These tables should be used in conjunction with sections 6.0 and 8.0 of the document.
Specifically the different acceptance criteria for Group A vs. Group B motors must be
observed when inspecting and dispositioning motors that have any type of failure or
degradation per the tables below.
BWROG-TP-09-005, Rev. 0
Inspection of MOV Magnesium Rotors, Appendix 3
Page 2 of 2
Motor Inspection Failure Criteria
Item Identified
Yes No
Any observed gap or separation between the rotor end lamination and
the magnesium end ring with evidence of corrosion at or near the gap
interface.
Any outward spreading or radial misalignment of any cooling fin. This
would normally be found in conjunction with the item above.
Black corrosion product build-up between the rotor end lamination and
the magnesium end ring.
Black corrosion product build-up at outside diameter of rotor at
magnesium end ring.
Indication of therma!ly induced stress. Obvious darkening or
discoloration of the magnesium end ring adjacent to the rotor end
lamination.
Balance nubs or outside edges of the cooling fins are corroded away.
This should not be confused with the factory removal of balance nubs or
grinding of the cooling fins during the rotor balance process.
The magnesium end ring is broken or has missing sections. Pieces of
the magnesium end ring or cooling fins are found detached within the
motor housing.
Globular or molten metallic deposits appear anywhere on the surface of
the magnesium end ring and/or cooling fins.
Any cracking in the magnesium end ring or the cooling fins, particularly
where the cooling fins join the magnesium end ring.
Any evidence of contact between the rotor cooling fins and the stator
windings.
Excessive corrosion or bubbling of the magnesium end ring or cooling
fins.
Motor Inspection Degradation Criteria
Item Identified
Yes No
Slight blistering of the protective coating of the magnesium end ring or
the cooling fins.
Minor pockets of corrosion on the magnesium end ring and/or the
cooling fins.
Minor galvanic corrosion at the interface of the magnesium end ring and
end lamination.
ENCLOSURE 3
AFFIDAVIT REQUESTING WITHOLDING OF ENCLOSURE 1
BWR Owners' Group
I, Douglas W. Coleman, state as follows:
(1) I, Chairman of the BWR Owners' Group (BWROG), have been delegated the function of
reviewing the information described in paragraph (2) which is sought to be withheld, and
have been authorized to apply for its withholding.
(2) The information sought to be withheld is contained in BWR Owners' Group (BWROG)
Report, BWROG-TP-09-005, Inspection of Motor Operated Valve Limitorque AC Motors
with Magnesium Rotors, March 5, 2009. The proprietary information in BWROG Report,
BWROG-TP-09-005, Inspection of Motor Operated Valve Limitorque AC Motors with
Magnesium Rotors, March 5, 2009, is identified by [[d.Qtte underline inside double square.
.br ack..ets. 31.]]. Figures and other large objects are identified with double square brackets
before and after the object. In each case, the superscript notation Q3) refers to Paragraph (3)
of this affidavit, which provides the basis for the proprietary determination.
(3) In making this application for withholding of proprietary information of which it is the
owner or licensee, BWROG relies upon the exemption from disclosure set forth in the
Freedom of Information Act ("FOIA"), 5 USC Sec. 552(b)(4), and the Trade Secrets Act,
18 USC Sec. 1905, and NRC regulations 10 CFR 9.17(a)(4), and 2.390(a)(4) for "trade
secrets" (Exemption 4). The material for which exemption from disclosure is here sought
also qualify under the narrower definition of "trade secret", within the meanings assigned to
those terms for purposes of FOIA Exemption 4 in, respectively, Critical Mass Energy
Proiect v. Nuclear Regulatory Commission, 975F2d871 (DC Cir. 1992), and Public Citizen
Health Research Group v. FDA, 704F2dl280 (DC Cir. 1983).
(4) Some examples of categories of information, which fit into the definition of proprietary
information, are:
a. Information that discloses a process, method, or apparatus, including supporting data
and analyses, where prevention of its use by BWROG's competitors without license
from BWROG constitutes a competitive economic advantage over other companies;
b. Information which, if used by a competitor, would reduce his expenditure of resources
or improve his competitive position in the design, manufacture, shipment, installation,
assurance of quality, or licensing of a similar product;
c. Information, which reveals aspects of past, present, or future BWROG customerfunded
development plans and programs, resulting in potential products to BWROG;
d. Information, which discloses patentable subject matter for which it may be desirable to
obtain patent protection.
The information sought to be withheld is considered to be proprietary for the reasons set
forth in paragraphs (4)a. and (4)b. above.
(5) To address 10 CFR 2.390(b)(4), the information sought to be withheld is being transmitted
to NRC in confidence. The information is of a sort customarily held in confidence by
BWROG, and is in fact so held. The information sought to be withheld has, to the best of
my knowledge and belief, consistently been held in confidence by BWROG, no public
disclosure has been made, and it is not available in public sources. All disclosures to third
parties, including any required transmittals to NRC, have been made, or must be made,
pursuant to regulatory provisions or proprietary agreements which provide for maintenance
of the information in confidence. Its initial designation as proprietary information, and the
subsequent steps taken to prevent its unauthorized disclosure, are as set forth in paragraphs
(6) and (7) following.
(6) Initial approval of proprietary treatment of a document is made by the manager of the
originating component, the person most likely to be acquainted with the value and
sensitivity of the information in relation to industry knowledge, or subject to the terms
under which it was licensed to BWROG. Access to such documents within BWROG is
limited on a "need to know" basis.
(7) The procedure for approval of external release of such a document typically requires review
by the staff manager, project manager, principal scientist, or other equivalent authority for
technical content, competitive effect, and determination of the accuracy of the proprietary
designation. Disclosures outside BWROG are limited to regulatory bodies, customers, and
potential customers, and their agents, suppliers, and licensees, and others with a legitimate
need for the information, and then only in accordance with appropriate regulatory
provisions or proprietary agreements.
(8) The information identified in paragraph (2), above, is classified as proprietary because it
contains detailed results of analytical models, methods and processes, including computer
codes, which BWROG has developed, and applied to perform licensing and design
evaluations for the BWR.
The development of the evaluation process along with the interpretation and application of
the analytical results is derived from the extensive experience database that constitutes a
major BWROG asset.
(9) Public disclosure of the information sought to be withheld is likely to cause substantial
harm to BWROG's competitive position and foreclose or reduce the availability of profitmaking
opportunities. The information is part of BWROG's comprehensive BWR safety
and technology base, and its commercial value extends beyond the original development
cost. The value of the technology base goes beyond the extensive physical database and
analytical methodology and includes development of the expertise to determine and apply
the appropriate evaluation process. In addition, the technology base includes the value
derived from providing analyses done with NRC-approved methods.
The research, development, engineering, analytical and NRC review costs comprise a
substantial investment of time and money by BWROG.
The precise value of the expertise to devise an evaluation process and apply the correct
analytical methodology is difficult to quantify, but it clearly is substantial.
BWROG's competitive advantage will be lost if its competitors are able to use the results of
the BWROG experience to normalize or verify their own process or if they are able to claim
an equivalent understanding by demonstrating that they can arrive at the same or similar
conclusions.
The value of this information to BWROG would be lost if the information were disclosed to
the public. Making such information available to competitors without their having been
required to undertake a similar expenditure of resources would unfairly provide competitors
with a windfall, and deprive BWROG of the opportunity to exercise its competitive
advantage to seek an adequate return on its large investment in developing and obtaining
these very valuable analytical tools.
I declare under penalty of perjury that the foregoing affidavit and the matters stated therein are
true and correct to the best of my knowledge, information, and belief.
Executed on this 14rh day of May 2009.
Douglas W. Coleman
Chairman
BWR Owners' Group