Information Notice 1988-12, Overgreasing of Electric Motor Bearings: Difference between revisions

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{{#Wiki_filter:UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555April 12, 1988NRC INFORMATION NOTICE NO.' 88-12: OVERGREASING OF ELECTRIC MOTOR BEARINGS
{{#Wiki_filter:UNITED STATES NUCLEAR REGULATORY
 
COMMISSION
 
===OFFICE OF NUCLEAR REACTOR REGULATION===
WASHINGTON, D.C. 20555 April 12, 1988 NRC INFORMATION
 
NOTICE NO.' 88-12: OVERGREASING
 
OF ELECTRIC MOTOR BEARINGS


==Addressees==
==Addressees==
:All holders of operating licenses or construction permits for nuclear powerreactors.
:
All holders of operating
 
licenses or construction
 
permits for nuclear power reactors.


==Purpose==
==Purpose==
:This information notice is being provided to alert addressees to problemscaused by accumulation of grease on electric motors used to drive rotatingequipment in nuclear power plants. It is expected that recipients willreview the information for applicability to their facilities and consider-actions, as appropriate, to avoid similar problems. However, suggestionscontained in-this information notice do not constitute NRC requirements;therefore, no specific action or written response is required.
: This information
 
notice is being provided to alert addressees
 
to problems caused by accumulation
 
of grease on electric motors used to drive rotating equipment
 
in nuclear power plants. It is expected that recipients
 
will review the information
 
for applicability
 
to their facilities
 
and consider-actions, as appropriate, to avoid similar problems.
 
===However, suggestions===
contained
 
in-this information
 
notice do not constitute
 
NRC requirements;
therefore, no specific action or written response is required.Description
 
of Circumstances:
NRC personnel
 
observed accumulations
 
of grease on the air vent screens of electric motors used for driving such rotating equipment
 
as fans and pumps at the Millstone
 
and Calvert Cliffs nuclear power plants. The grease ap-peared to have come from overgreasing
 
of the electric motor bearings.
 
Grease was forced out of the bearing seals, onto the stator windings and rotor, from where it either fell or was thrown onto the inside'of
 
the motor housing. Be-cause of these observations, the NRC began an investigation
 
'into problems that have been caused in the past, or could be caused in the future, by the over-greasing of electric motor bearings.Several electric motor overgreasing
 
events were identified
 
that have led to failures of nuclear plant components:
°- 'At a nuclear plant in 1975, overgreasing
 
of the motor bearings caused the failure of the containment
 
cooler fans when 'a bearing failed and seized.° At Susquehanna
 
Unit 1, on July 24, 1984, excessive'grease
 
buildup in the Selectric
 
motor of a motor generator
 
set caused the set to'shut down and resulted in the spurious emergency
 
actuations
 
of the standby gas treatment system and the control room emergency
 
outside air system (LER 387/84-036).( 8000370
IN 88-12 April 12, 1988 0 At Palisades
 
Unit 1, overgreasing
 
of the motor bearings caused the contain-ment cooler fans to fall on three different
 
occasions:
On July 7, 1986, overgreasing
 
of the motor shaft bearings caused the bearings to skid in-stead of roll. This caused the motor to overheat and automatically
 
shut down. On August 8, 1986, and again on August 11, 1986, overgreasing
 
caused the motor bearings to deteriorate
 
which, in turn, caused the motor and fan to vibrate, and bolts on the equipment
 
to loosen and fall (LER 255/86-031).
 
In addition to these overgreasing
 
events, a number of cases have been reported in which excessive
 
motor bearing grease caused problems that were caught before the systems actually failed. For example, at a nuclear plant in 1978, exces-sive grease in a motor bearing in the service-water
 
system caused the bearing to become abnormally
 
hot and noisy. At another nuclear plant in 1986, grease from a bearing in the component
 
cooling pump motor ran into the motor, causing it to smoke.Discussion:
The NRC staff has solicited
 
technical
 
information
 
and operating
 
experience
 
on the problems caused by the overgreasing
 
of electric motor bearings from motor and bearing manufacturers, as well as from other licensees.
 
Their responses are summarized
 
in this discussion.
 
Two basic mechanisms
 
involving
 
overgreasing
 
of bearings can lead to the failure of electric motors: (1) The excess grease will leak out from the bearing seal and be deposited on the stator and rotor windings.
 
The grease deposits create a thermal barrier between the windings and their cooling air, leading to an increase in motor temperature.
 
For motors designed to use outside air to cool the windings, the temperature
 
is increased
 
still more by the buildup of dirt, dust, and other foreign materials
 
that adhere to the grease. It is esti-mated that for every 10F rise in motor temperature, the insulation
 
life of the windings is reduced by half. The deterioration
 
of the winding insulation
 
then causes the motor to "short out".(2) The excess grease causes a "churning" action of the ball bearings within their housing, increasing
 
the temperature
 
of the grease and bearings.As the temperature
 
approaches
 
the upper functional
 
design limit of the grease, viscous or hard residues form, causing a breakdown
 
of the lubri-cating characteristics
 
of the grease. The bearing temperature
 
then rises higher, and eventually
 
causes a reduction
 
in bearing hardness and a sub-sequent breakdown
 
of the bearing. A rule of thumb, based on certain
 
IN 88-12 April 12, 1988 manufacturers
 
1 tests, is that grease life is halved for every 25 0 F increase in temperature
 
and is doubled for every 25 0 F decrease in temperature.
 
High bearing temperature
 
may also cause the inner race of the bearing to expand and slip on the rotor shaft. The expansion
 
and slippage of the bearing's
 
inner race leads to a misalignment
 
between the rotor shaft and the bearing; this misalignment
 
can cause contact between the rotor and stator. Once contact occurs, the windings short and burn out.One frequent cause of excess grease problems is the failure to provide an exit path for the displaced
 
grease when new grease is added. This can result from the failure to remove the grease drain plug, or from failure to unblock drain lines that have become plugged by hardened grease or dirt. Another frequent cause is the addition of too much grease. The correct amount must be deter-mined for each situation.
 
Bearing manufacturers
 
generally
 
recommend
 
filling the motor bearing void space from one-third
 
to one-half full of grease. How-ever, the optimum amount can vary from 20% to 80% full, depending
 
on such factors as the application
 
of the motor, the environment
 
of the motor, the retainer design, and the type of grease.The following
 
actions can be taken to correct or prevent motor overgreasing
 
and related problems: (1) Review motor lubrication
 
procedures
 
to ensure that they identify the type and quantity of grease to use, the specific fill and drain nozzles to uncap, and the length of time motors should be run with drain plugs off after greasing the bearings.(2) To prevent foreign materials
 
from contaminating
 
the grease, ensure that grease containers
 
are covered during periods of storage and that nozzles and grease fittings are cleaned.(3) Determine
 
the optimum quantity and correct type of grease required for each motor by examining
 
the manufacturer's
 
recommendations
 
and by monitor-Ing the behavior of grease added to motors.(4) Consider using prelubricated
 
sealed bearings in applications
 
where re-lubrication
 
is difficult, where contaminants
 
can adulterate
 
the grease, or where overgreasing
 
might damage safety systems.It should be noted that the vast majority of the reported lubrication-related
 
incidents
 
have been the result of underlubrication
 
rather than overlubrication.
 
This notice is not intended to discourage
 
the adequate lubrication
 
of motor bearings, but to prevent overgreasing
 
problems by encouraging
 
a thorough under-standing of correct lubrication
 
procedures.
 
<- -o IN 88-12 April 12, 1988 No specific action or written response is required by this information
 
notice.If you have any questions
 
about this matter, please contact the technical contact listed below or the Regional Administrator
 
of the appropriate
 
regional office.Zarles E. Rossi Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
Contacts:
James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:
List of Recently Issued NRC Information
 
Notices
 
IY-Attachment
 
IN 88-12 April 12, 1988 LIST OF RECENTLY ISSUED NRC INFORMATION
 
NOTICES Information
 
Date of Notice No. Subject Issuance Issued to 88-11 88-10 87-44, Supp. 1 88-09 88-08 88-07 88-06 88-05 Potential
 
Loss of Motor Control Center and/or Switchboard
 
Function Due to Faulty Tie Bolts Materials
 
Licensees:
Lack of Management
 
Controls Over Licensed Programs Thimble Tube Thinning in Westinghouse
 
Reactors Reduced Reliability
 
of Steam-Driven
 
Auxiliary Feedwater
 
Pumps Caused by Instability
 
of Woodward PG-PL Governors Chemical Reactions
 
with Radioactive
 
Waste Solidification
 
Agents Inadvertent
 
Transfer of Licensed Material to Uncontrolled
 
===Locations Foreign Objects in Steam Generators===
Fire in Annunciator
 
Control Cabinets 4/7/88 3/28/88 3/28/88 3/18/88 3/14/88 3/7/88 2/29/88 2/11/88 All holders of OLs or CPs for nuclear power reactors.All NRC licensees authorized
 
to use byproduct
 
material.All holders of OLs or CPs for nuclear power reactors that employ a Westinghouse
 
NSSS.All holders of OLs or CPs for nuclear power reactors.All NRC licensees generating
 
or pro-cessing low level radioactive
 
waste.All NRC broad licensees and licensees
 
authorized
 
to possess byproduct material as sealed sources in teletherapy
 
units or 'self-contained" irradiators.
 
All holders of OLs or CPs for PWRs.All holders of OLs or CPs for nuclear power reactors.OL = Operating
 
License CP = Construction
 
Permit
 
-IN 88-12 April 12, 1988 No specific action or written response is required by this information
 
notice.If you have any questions
 
about this matter, please contact the technical contact listed below or the Regional Administrator
 
of the appropriate
 
regional office.Charles E. Rossi, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:
List of Recently Issued NRC Information
 
Notices*SEE PREVIOUS CONCURRENCES
 
04/h/88 \*SELB:DEST:NRR
 
FRosa 03/28/88*OGCB:DOEA:NRR
 
===DCKirkpatrick===
03/24/88*C/OGCB:DOEA:NRR*PPMB:ARM
 
CHBerlinger
 
TechEd 04/04/88 03/30/88*TPAB:DSP:AEOD
 
*D/DEST:NRR
 
MRHarper LCShao 03/28/88 04/05/88*RI JAPrell 03/25/88
1.1 4 -IN 88-XX April xx, 1988 No specific action or written response is required by this information
 
notice.If you have any questions
 
about this matter, please contact the technical contact listed below or the Regional Administrator
 
of the appropriate
 
regional office.Charles E. Rossi, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:
List of Recently Issued NRC Information
 
Notices*SEE PREVIOUS CONCURRENCES
 
D/DWEA:NRR
 
CERossi 04/ /88*SELB:DEST:NRR
 
FRosa 03/28/88*OGCB:DOEA:NRR
 
===DCKirkpatrick===
03/24/88*RI JAPrel 1 03/25/88*C/OGCB:DOEA:NRR*PPMB:ARM
 
CHBerlinger
 
TechEd 04/04/88 03/30/88*TPAB:DSP:AEOD
 
D/DEST:NRR
 
MRHarper LCShao 03/28/88 04 {_8' I
 
x'* j _IN 88-XX April xx, 1988 No specific action or written response is required by this information
 
notice.If you have any questions
 
about this matter, please contact the technical contact listed below or the Regional Administrator
 
of the appropriate
 
regional office.Charles E. Rossi, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Reaulation
 
Technical
 
Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:
List of Recently Issued NRC Information
 
Notices*SEE PREVIOUS CONCURRENCES
 
D/DOEA:NRR
 
CERossi 04/ /88*TPAB:DSP:AEOD
 
MRHarper 03/28/88 C 4 C/OGCB: DOEA: NRR CHBerlinger
 
044 /88*P4B:ARM TechEd 03/30/88*OGCB:DOEA:NRR
 
===DCKirkpatrick===
03/24/88*RI JAPrel 1 03/25/88*SELB:DEST:NRR
 
FRosa 03/28/88 IN 88-XX March xx, 1988 No specific action or written response is required by this information
 
notice.If you have any questions
 
about this matter, please contact the technical contact listed below or the Regional Administrator
 
of the appropriate
 
regional office.Charles E. Rossi, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:
List of Recently Issued NRC Information
 
Notices*Transmitted
 
by dated OGCB:DOEA:NRR


==Description of Circumstances==
===DCKlirkpatric===
:NRC personnel observed accumulations of grease on the air vent screens ofelectric motors used for driving such rotating equipment as fans and pumpsat the Millstone and Calvert Cliffs nuclear power plants. The grease ap-peared to have come from overgreasing of the electric motor bearings. Greasewas forced out of the bearing seals, onto the stator windings and rotor, fromwhere it either fell or was thrown onto the inside'of the motor housing. Be-cause of these observations, the NRC began an investigation 'into problems thathave been caused in the past, or could be caused in the future, by the over-greasing of electric motor bearings.Several electric motor overgreasing events were identified that have led tofailures of nuclear plant components:&deg;- 'At a nuclear plant in 1975, overgreasing of the motor bearings caused thefailure of the containment cooler fans when 'a bearing failed and seized.&deg; At Susquehanna Unit 1, on July 24, 1984, excessive'grease buildup in theSelectric motor of a motor generator set caused the set to'shut down andresulted in the spurious emergency actuations of the standby gas treatmentsystem and the control room emergency outside air system (LER 387/84-036).( 8000370
03i /88 D?/RI A5L *4 SELB:DEST:NRR
IN 88-12April 12, 1988 At Palisades Unit 1, overgreasing of the motor bearings caused the contain-ment cooler fans to fall on three different occasions: On July 7, 1986,overgreasing of the motor shaft bearings caused the bearings to skid in-stead of roll. This caused the motor to overheat and automatically shutdown. On August 8, 1986, and again on August 11, 1986, overgreasing causedthe motor bearings to deteriorate which, in turn, caused the motor and fanto vibrate, and bolts on the equipment to loosen and fall (LER 255/86-031).In addition to these overgreasing events, a number of cases have been reportedin which excessive motor bearing grease caused problems that were caught beforethe systems actually failed. For example, at a nuclear plant in 1978, exces-sive grease in a motor bearing in the service-water system caused the bearingto become abnormally hot and noisy. At another nuclear plant in 1986, greasefrom a bearing in the component cooling pump motor ran into the motor, causingit to smoke.Discussion:The NRC staff has solicited technical information and operating experience onthe problems caused by the overgreasing of electric motor bearings from motorand bearing manufacturers, as well as from other licensees. Their responsesare summarized in this discussion.Two basic mechanisms involving overgreasing of bearings can lead to the failureof electric motors:(1) The excess grease will leak out from the bearing seal and be depositedon the stator and rotor windings. The grease deposits create a thermalbarrier between the windings and their cooling air, leading to an increasein motor temperature. For motors designed to use outside air to cool thewindings, the temperature is increased still more by the buildup of dirt,dust, and other foreign materials that adhere to the grease. It is esti-mated that for every 10F rise in motor temperature, the insulation lifeof the windings is reduced by half. The deterioration of the windinginsulation then causes the motor to "short out".(2) The excess grease causes a "churning" action of the ball bearings withintheir housing, increasing the temperature of the grease and bearings.As the temperature approaches the upper functional design limit of thegrease, viscous or hard residues form, causing a breakdown of the lubri-cating characteristics of the grease. The bearing temperature then riseshigher, and eventually causes a reduction in bearing hardness and a sub-sequent breakdown of the bearing. A rule of thumb, based on certain


IN 88-12April 12, 1988 manufacturers1 tests, is that grease life is halved for every 250Fincrease in temperature and is doubled for every 250F decrease intemperature.High bearing temperature may also cause the inner race of the bearing toexpand and slip on the rotor shaft. The expansion and slippage of thebearing's inner race leads to a misalignment between the rotor shaft andthe bearing; this misalignment can cause contact between the rotor andstator. Once contact occurs, the windings short and burn out.One frequent cause of excess grease problems is the failure to provide an exitpath for the displaced grease when new grease is added. This can result fromthe failure to remove the grease drain plug, or from failure to unblock drainlines that have become plugged by hardened grease or dirt. Another frequentcause is the addition of too much grease. The correct amount must be deter-mined for each situation. Bearing manufacturers generally recommend fillingthe motor bearing void space from one-third to one-half full of grease. How-ever, the optimum amount can vary from 20% to 80% full, depending on suchfactors as the application of the motor, the environment of the motor, theretainer design, and the type of grease.The following actions can be taken to correct or prevent motor overgreasingand related problems:(1) Review motor lubrication procedures to ensure that they identify thetype and quantity of grease to use, the specific fill and drain nozzlesto uncap, and the length of time motors should be run with drain plugsoff after greasing the bearings.(2) To prevent foreign materials from contaminating the grease, ensure thatgrease containers are covered during periods of storage and that nozzlesand grease fittings are cleaned.(3) Determine the optimum quantity and correct type of grease required foreach motor by examining the manufacturer's recommendations and by monitor-Ing the behavior of grease added to motors.(4) Consider using prelubricated sealed bearings in applications where re-lubrication is difficult, where contaminants can adulterate the grease,or where overgreasing might damage safety systems.It should be noted that the vast majority of the reported lubrication-relatedincidents have been the result of underlubrication rather than overlubrication.This notice is not intended to discourage the adequate lubrication of motorbearings, but to prevent overgreasing problems by encouraging a thorough under-standing of correct lubrication procedures.
JAPrell FRosa fIt Phefi 03/AQ788 03/2t/88 D/DOEA:NRR


<- -oIN 88-12April 12, 1988 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Zarles E. Rossi DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152Attachment: List of Recently Issued NRC Information Notices
CERossi 03/ /88 TPAB:DSP:AEOD


IY-AttachmentIN 88-12April 12, 1988 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to88-1188-1087-44,Supp. 188-0988-0888-0788-0688-05Potential Loss of MotorControl Center and/orSwitchboard Function Dueto Faulty Tie BoltsMaterials Licensees: Lackof Management Controls OverLicensed ProgramsThimble Tube Thinning inWestinghouse ReactorsReduced Reliability ofSteam-Driven AuxiliaryFeedwater Pumps Causedby Instability of WoodwardPG-PL GovernorsChemical Reactions withRadioactive WasteSolidification AgentsInadvertent Transfer ofLicensed Material toUncontrolled LocationsForeign Objects in SteamGeneratorsFire in Annunciator ControlCabinets4/7/883/28/883/28/883/18/883/14/883/7/882/29/882/11/88All holders of OLsor CPs for nuclearpower reactors.All NRC licenseesauthorized to usebyproduct material.All holders of OLsor CPs for nuclearpower reactors thatemploy a WestinghouseNSSS.All holders of OLsor CPs for nuclearpower reactors.All NRC licenseesgenerating or pro-cessing low levelradioactive waste.All NRC broad licenseesand licensees authorizedto possess byproductmaterial as sealedsources in teletherapyunits or 'self-contained"irradiators.All holders of OLsor CPs for PWRs.All holders of OLsor CPs for nuclearpower reactors.OL = Operating LicenseCP = Construction Permit
MRHarper i 03/2[r/88 A C/OGCB:DOEA:NRR


-IN 88-12April 12, 1988 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152Attachment:List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCES04/h/88 \*SELB:DEST:NRRFRosa03/28/88*OGCB:DOEA:NRRDCKirkpatrick03/24/88*C/OGCB:DOEA:NRR*PPMB:ARMCHBerlinger TechEd04/04/88 03/30/88*TPAB:DSP:AEOD *D/DEST:NRRMRHarper LCShao03/28/88 04/05/88*RIJAPrell03/25/88
CHBerlinger
1.1 4 -IN 88-XXApril xx, 1988 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152Attachment:List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCESD/DWEA:NRRCERossi04/ /88*SELB:DEST:NRRFRosa03/28/88*OGCB:DOEA:NRRDCKirkpatrick03/24/88*RIJAPrel 103/25/88*C/OGCB:DOEA:NRR*PPMB:ARMCHBerlinger TechEd04/04/88 03/30/88*TPAB:DSP:AEOD D/DEST:NRRMRHarper LCShao03/28/88 04 {_8' I


x'* j _IN 88-XXApril xx, 1988 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor ReaulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152Attachment:List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCESD/DOEA:NRRCERossi04/ /88*TPAB:DSP:AEODMRHarper03/28/88C 4C/OGCB: DOEA: NRRCHBerlinger044 /88*P4B:ARMTechEd03/30/88*OGCB:DOEA:NRRDCKirkpatrick03/24/88*RIJAPrel 103/25/88*SELB:DEST:NRRFRosa03/28/88 IN 88-XXMarch xx, 1988 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152Attachment:List of Recently Issued NRC Information Notices*Transmitted bydatedOGCB:DOEA:NRRDCKlirkpatric03i /88 D?/RI A5L *4SELB:DEST:NRRJAPrell FRosa fIt Phefi03/AQ788 03/2t/88D/DOEA:NRRCERossi03/ /88TPAB:DSP:AEODMRHarper i03/2[r/88 AC/OGCB:DOEA:NRRCHBerlinger03/ /88PPMB:ARMTechEd i 903/Jo/88 Wo '  
03/ /88 PPMB:ARM TechEd i 9 03/Jo/88 Wo '}}
}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Revision as of 13:29, 31 August 2018

Overgreasing of Electric Motor Bearings
ML031150512
Person / Time
Site: Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date: 04/12/1988
From: Rossi C E
Office of Nuclear Reactor Regulation
To:
References
IN-88-012, NUDOCS 8804060370
Download: ML031150512 (9)
v • d • e


UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 April 12, 1988 NRC INFORMATION

NOTICE NO.' 88-12: OVERGREASING

OF ELECTRIC MOTOR BEARINGS

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.

Purpose

This information

notice is being provided to alert addressees

to problems caused by accumulation

of grease on electric motors used to drive rotating equipment

in nuclear power plants. It is expected that recipients

will review the information

for applicability

to their facilities

and consider-actions, as appropriate, to avoid similar problems.

However, suggestions

contained

in-this information

notice do not constitute

NRC requirements;

therefore, no specific action or written response is required.Description

of Circumstances:

NRC personnel

observed accumulations

of grease on the air vent screens of electric motors used for driving such rotating equipment

as fans and pumps at the Millstone

and Calvert Cliffs nuclear power plants. The grease ap-peared to have come from overgreasing

of the electric motor bearings.

Grease was forced out of the bearing seals, onto the stator windings and rotor, from where it either fell or was thrown onto the inside'of

the motor housing. Be-cause of these observations, the NRC began an investigation

'into problems that have been caused in the past, or could be caused in the future, by the over-greasing of electric motor bearings.Several electric motor overgreasing

events were identified

that have led to failures of nuclear plant components:

°- 'At a nuclear plant in 1975, overgreasing

of the motor bearings caused the failure of the containment

cooler fans when 'a bearing failed and seized.° At Susquehanna

Unit 1, on July 24, 1984, excessive'grease

buildup in the Selectric

motor of a motor generator

set caused the set to'shut down and resulted in the spurious emergency

actuations

of the standby gas treatment system and the control room emergency

outside air system (LER 387/84-036).( 8000370

IN 88-12 April 12, 1988 0 At Palisades

Unit 1, overgreasing

of the motor bearings caused the contain-ment cooler fans to fall on three different

occasions:

On July 7, 1986, overgreasing

of the motor shaft bearings caused the bearings to skid in-stead of roll. This caused the motor to overheat and automatically

shut down. On August 8, 1986, and again on August 11, 1986, overgreasing

caused the motor bearings to deteriorate

which, in turn, caused the motor and fan to vibrate, and bolts on the equipment

to loosen and fall (LER 255/86-031).

In addition to these overgreasing

events, a number of cases have been reported in which excessive

motor bearing grease caused problems that were caught before the systems actually failed. For example, at a nuclear plant in 1978, exces-sive grease in a motor bearing in the service-water

system caused the bearing to become abnormally

hot and noisy. At another nuclear plant in 1986, grease from a bearing in the component

cooling pump motor ran into the motor, causing it to smoke.Discussion:

The NRC staff has solicited

technical

information

and operating

experience

on the problems caused by the overgreasing

of electric motor bearings from motor and bearing manufacturers, as well as from other licensees.

Their responses are summarized

in this discussion.

Two basic mechanisms

involving

overgreasing

of bearings can lead to the failure of electric motors: (1) The excess grease will leak out from the bearing seal and be deposited on the stator and rotor windings.

The grease deposits create a thermal barrier between the windings and their cooling air, leading to an increase in motor temperature.

For motors designed to use outside air to cool the windings, the temperature

is increased

still more by the buildup of dirt, dust, and other foreign materials

that adhere to the grease. It is esti-mated that for every 10F rise in motor temperature, the insulation

life of the windings is reduced by half. The deterioration

of the winding insulation

then causes the motor to "short out".(2) The excess grease causes a "churning" action of the ball bearings within their housing, increasing

the temperature

of the grease and bearings.As the temperature

approaches

the upper functional

design limit of the grease, viscous or hard residues form, causing a breakdown

of the lubri-cating characteristics

of the grease. The bearing temperature

then rises higher, and eventually

causes a reduction

in bearing hardness and a sub-sequent breakdown

of the bearing. A rule of thumb, based on certain

IN 88-12 April 12, 1988 manufacturers

1 tests, is that grease life is halved for every 25 0 F increase in temperature

and is doubled for every 25 0 F decrease in temperature.

High bearing temperature

may also cause the inner race of the bearing to expand and slip on the rotor shaft. The expansion

and slippage of the bearing's

inner race leads to a misalignment

between the rotor shaft and the bearing; this misalignment

can cause contact between the rotor and stator. Once contact occurs, the windings short and burn out.One frequent cause of excess grease problems is the failure to provide an exit path for the displaced

grease when new grease is added. This can result from the failure to remove the grease drain plug, or from failure to unblock drain lines that have become plugged by hardened grease or dirt. Another frequent cause is the addition of too much grease. The correct amount must be deter-mined for each situation.

Bearing manufacturers

generally

recommend

filling the motor bearing void space from one-third

to one-half full of grease. How-ever, the optimum amount can vary from 20% to 80% full, depending

on such factors as the application

of the motor, the environment

of the motor, the retainer design, and the type of grease.The following

actions can be taken to correct or prevent motor overgreasing

and related problems: (1) Review motor lubrication

procedures

to ensure that they identify the type and quantity of grease to use, the specific fill and drain nozzles to uncap, and the length of time motors should be run with drain plugs off after greasing the bearings.(2) To prevent foreign materials

from contaminating

the grease, ensure that grease containers

are covered during periods of storage and that nozzles and grease fittings are cleaned.(3) Determine

the optimum quantity and correct type of grease required for each motor by examining

the manufacturer's

recommendations

and by monitor-Ing the behavior of grease added to motors.(4) Consider using prelubricated

sealed bearings in applications

where re-lubrication

is difficult, where contaminants

can adulterate

the grease, or where overgreasing

might damage safety systems.It should be noted that the vast majority of the reported lubrication-related

incidents

have been the result of underlubrication

rather than overlubrication.

This notice is not intended to discourage

the adequate lubrication

of motor bearings, but to prevent overgreasing

problems by encouraging

a thorough under-standing of correct lubrication

procedures.

<- -o IN 88-12 April 12, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Zarles E. Rossi Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts:

James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices

IY-Attachment

IN 88-12 April 12, 1988 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 88-11 88-10 87-44, Supp. 1 88-09 88-08 88-07 88-06 88-05 Potential

Loss of Motor Control Center and/or Switchboard

Function Due to Faulty Tie Bolts Materials

Licensees:

Lack of Management

Controls Over Licensed Programs Thimble Tube Thinning in Westinghouse

Reactors Reduced Reliability

of Steam-Driven

Auxiliary Feedwater

Pumps Caused by Instability

of Woodward PG-PL Governors Chemical Reactions

with Radioactive

Waste Solidification

Agents Inadvertent

Transfer of Licensed Material to Uncontrolled

Locations Foreign Objects in Steam Generators

Fire in Annunciator

Control Cabinets 4/7/88 3/28/88 3/28/88 3/18/88 3/14/88 3/7/88 2/29/88 2/11/88 All holders of OLs or CPs for nuclear power reactors.All NRC licensees authorized

to use byproduct

material.All holders of OLs or CPs for nuclear power reactors that employ a Westinghouse

NSSS.All holders of OLs or CPs for nuclear power reactors.All NRC licensees generating

or pro-cessing low level radioactive

waste.All NRC broad licensees and licensees

authorized

to possess byproduct material as sealed sources in teletherapy

units or 'self-contained" irradiators.

All holders of OLs or CPs for PWRs.All holders of OLs or CPs for nuclear power reactors.OL = Operating

License CP = Construction

Permit

-IN 88-12 April 12, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCES

04/h/88 \*SELB:DEST:NRR

FRosa 03/28/88*OGCB:DOEA:NRR

DCKirkpatrick

03/24/88*C/OGCB:DOEA:NRR*PPMB:ARM

CHBerlinger

TechEd 04/04/88 03/30/88*TPAB:DSP:AEOD

  • D/DEST:NRR

MRHarper LCShao 03/28/88 04/05/88*RI JAPrell 03/25/88

1.1 4 -IN 88-XX April xx, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCES

D/DWEA:NRR

CERossi 04/ /88*SELB:DEST:NRR

FRosa 03/28/88*OGCB:DOEA:NRR

DCKirkpatrick

03/24/88*RI JAPrel 1 03/25/88*C/OGCB:DOEA:NRR*PPMB:ARM

CHBerlinger

TechEd 04/04/88 03/30/88*TPAB:DSP:AEOD

D/DEST:NRR

MRHarper LCShao 03/28/88 04 {_8' I

x'* j _IN 88-XX April xx, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Reaulation

Technical

Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCES

D/DOEA:NRR

CERossi 04/ /88*TPAB:DSP:AEOD

MRHarper 03/28/88 C 4 C/OGCB: DOEA: NRR CHBerlinger

044 /88*P4B:ARM TechEd 03/30/88*OGCB:DOEA:NRR

DCKirkpatrick

03/24/88*RI JAPrel 1 03/25/88*SELB:DEST:NRR

FRosa 03/28/88 IN 88-XX March xx, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*Transmitted

by dated OGCB:DOEA:NRR

DCKlirkpatric

03i /88 D?/RI A5L *4 SELB:DEST:NRR

JAPrell FRosa fIt Phefi 03/AQ788 03/2t/88 D/DOEA:NRR

CERossi 03/ /88 TPAB:DSP:AEOD

MRHarper i 03/2[r/88 A C/OGCB:DOEA:NRR

CHBerlinger

03/ /88 PPMB:ARM TechEd i 9 03/Jo/88 Wo '


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