Information Notice 1996-48, Motor-Operated Valve Performance Issues: Difference between revisions
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
||
Line 14: | Line 14: | ||
| page count = 13 | | page count = 13 | ||
}} | }} | ||
{{#Wiki_filter:l | {{#Wiki_filter:l | ||
UNITED STATES | |||
NUCLEAR REGULATORY COMMISSION | |||
OFFICE OF NUCLEAR REACTOR REGULATION | |||
VALVE PERFORMANCE | WASHINGTON, D.C. 20555-0001 August 21, 1996 NRC INFORMATION NOTICE 96-48: MOTOR-OPERATED VALVE PERFORMANCE ISSUES | ||
ISSUES | |||
==Addressees== | ==Addressees== | ||
All holders of operating | All holders of operating licenses or construction permits for nuclear power | ||
licenses or construction | |||
reactors. | |||
==Purpose== | ==Purpose== | ||
The U.S. Nuclear Regulatory | The U.S. Nuclear Regulatory Commission (NRC) is issuing this information | ||
Commission (NRC) is issuing | |||
notice | notice to alert addressees to (1) lessons learned from the Electric Power | ||
Research Institute (EPRI) Motor-Operated Valve (MOV) Performance Prediction | |||
problems with | Program, (2)performance problems with MOV key failures described in a recent | ||
of | NRC Office for Analysis and Evaluation of Operational Data (AEOD) study, and | ||
MOV | (3)the potential for torque output from MOV actuators to be less than | ||
predicted by Limitorque Corporation. 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 are not NRC requirements; therefore, no | |||
specific action or written response is required. | |||
Background | |||
In the 1980s. continuing problems with the performance of MOVs at nuclear | |||
power plants raised concerns regarding MOV design, testing, and maintenance. | |||
In response to these problems, both the nuclear industry and NRC initiated | |||
of MOVs | efforts to improve the performance of MOVs at nuclear plants. In 1989, the | ||
NRC staff issued Generic Letter (GL) 89-10, "Safety-Related Motor-Operated | |||
Valve Testing and Surveillance," requesting that nuclear power plant licensees | |||
of | and construction permit holders verify the design-basis capability of their | ||
safety-related MOVs. In response to GL 89-10, the nuclear industry has | |||
studied the performance of MOVs through testing and analyses. As a result of | |||
these activities, some weaknesses in the design and manufacture of MOVs were | |||
discovered through evaluation of the performance history of MOVs. In this | |||
three issues involving | information notice, the staff discusses three issues involving MOV performance | ||
that have been identified. | that have been identified. | ||
Description | ==Description of Circumstances== | ||
1. Lessons Learned from EPRI MOV Performance Prediction Program | |||
of Circumstances | |||
1. Lessons Learned from EPRI MOV Performance | |||
Prediction | |||
Program | |||
As part of the industry effort regarding the MOV issue. EPRI initiated an MOV | |||
Performance Prediction Program to develop a methodology to be used by | |||
licensees in demonstrating the design-basis capability of MOVs when valve- specific design-basis test data are not available. The program included | |||
9608150028 I | |||
PX 4\\\s 1-Dv-11C/if | |||
IN 96-48 August 21, 1996 development of improved methods for prediction or evaluation of system flow | |||
parameters; gate, globe, and butterfly valve performance: and motor actuator | |||
rate-of-loading effects (load-sensitive behavior). Further, EPRI performed | |||
and | testing to provide information for refining the gate valve model and rate-of- loading methods and conducted numerous MOV tests to provide data for model and | ||
method development and validation, including flow loop testing, parametric | |||
flow loop testing of butterfly valve disk designs, and in situ MOV testing. | |||
In November 1994, the Nuclear Energy Institute (NEI) submitted the proprietary | |||
EPRI Topical Report TR-103237, "EPRI MOV Performance Prediction Program - | |||
Topical Report," for review by the NRC staff. EPRI prepared 25 additional | |||
reports to support the topical report. On March 15, 1996, the NRC staff | |||
issued a Safety Evaluation (SE) documenting the staff review of the topical | |||
report. With the conditions and limitations described in the SE, the staff | |||
stated that the EPRI program provides an acceptable methodology to predict the | |||
and | thrust or torque required to operate gate, globe, and butterfly valves within | ||
and | the scope of the EPRI program and to bound the effects of load-sensitive | ||
behavior on motor actuator thrust output. | |||
In a letter dated September 27, 1995, NEI forwarded a summary of important | |||
contributions and findings resulting from the EPRI MOV Performance Prediction | |||
Program. As described in an enclosure to the NEI letter, important findings | |||
(or confirmatory information) from the EPRI MOV program include the following: | |||
a. The traditional methods for predicting gate valve performance might be | |||
for | nonconservative for many applications because of incomplete equations. | ||
design features, manufacturing controls, and wide-ranging friction | |||
coefficients. | |||
b. The edge radii on disk seats and guide slots are critical to gate valve | |||
performance and predictability. | |||
c. Stellite friction coefficients increase with differential-pressure valve | |||
strokes in cold water to a plateau level, stabilize quickly in hot | |||
water, and decrease as differential pressure increases. | |||
d. Gate valves with carbon steel guides and disk guide slots with tight | |||
clearances might fail to close under blowdown conditions. | |||
e. Many existing gate valve manufacturing and design processes and | |||
controls, and plant maintenance practices, might contribute to poor | |||
valve performance. | |||
f. Traditional methods for predicting globe valve performance for | |||
incompressible flow conditions are nonconservative for globe valves in | |||
which differential pressure acts across the plug guide. | |||
' IN 96-48 August 21. 1996 g. Globe valve thrust requirements for some designs can be excessive under | |||
compressible flow and blowdown conditions because of the potential for | |||
plug-side loading. | |||
h. Rate-of-loading effects (load-sensitive behavior) can reduce the static | |||
thrust output by up to 30 percent under dynamic conditions. | |||
i. Hydrodynamic torque coefficients used by some butterfly valve | |||
manufacturers might be nonconservative for certain applications, with | |||
valves located near piping elbows especially vulnerable. | |||
j. Butterfly valve seats should be periodically replaced to avoid hardening | |||
or degradation. | |||
that thrust | In addition to these reported important findings, EPRI confirmed that thrust | ||
to unwedge a gate valve can be higher under dynamic conditions | requirements to unwedge a gate valve can be higher under dynamic conditions | ||
than under static conditions. | than under static conditions. | ||
2. MOV Key Failures | 2. MOV Key Failures | ||
On March 29. 1996. AEOD issued report AEOD/E96-01. entitled, "Engineering | |||
Evaluation - Motor-Operated Valve Key Failures," on the continuing occurrence | |||
of problems with keys in MOVs at nuclear power plants. A significant number | |||
of MOV key failures have been identified that involved (a)anti-rotation keys. | |||
(b)valve operator-to-valve stem keys. and (c)motor pinion gear keys. A | |||
total of 73 reports were written involving MOV key failures between January | |||
1990 through September 1995. Many of these key failures were not detected | |||
during surveillance tests but were detected on demand, during valve | |||
for | operations. or during maintenance activities and had existed for some time | ||
before they were discovered. A number of key failures were discovered during | |||
maintenance activities even though the valves had been operated satisfactorily | |||
and passed all previous surveillance tests. | |||
3. Limitorque Motor Actuator Performance | |||
the | In 1977. Limitorque Corporation established guidelines (referred to as the SEL | ||
documents) for sizing ac-powered motor actuators used in MOVs. Those | |||
guidelines predicted the motor actuator output torque as a product of the | |||
nominal motor-rated start torque. pullout efficiency, application factor | |||
(typically 0.9), overall actuator gear ratio, and a degraded voltage factor. | |||
Over the past few years, Limitorque has accepted the use of run efficiency for | |||
closing valves powered by ac-powered motor actuators. Limitorque has also | |||
stated that licensees may eliminate the application factor when voltage | |||
supplied to the motor is less than 90 percent of its rated voltage. (See | |||
Limitorque Technical Update 93-03 [Accession 9608120083].) Recent industry | |||
IN 96-48 August 21. 1996 and NRC-sponsored test information has raised questions regarding the accuracy | |||
for actuator efficiency. | of the Limitorque assumptions for actuator efficiency. | ||
Discussion | Discussion | ||
1. Lessons Learned from the EPRI MOV Performance | 1. Lessons Learned from the EPRI MOV Performance Prediction Program | ||
Prediction | |||
Program | |||
As discussed in the staff SE on the EPRI topical report, the EPRI program | |||
the | provided important information on the design, testing. and maintenance of MOVs | ||
in nuclear power plants. Some of the EPRI information is applicable to gate. | |||
globe, and butterfly valves regardless of the type of actuator operating the | |||
valve. Examples of such information are given below: | |||
Gate Valves | |||
Almost all flow testing by licensees in response to GL 89-10 was conducted | |||
under pumped-flow conditions. Several gate valves tested by EPRI under | |||
blowdown conditions demonstrated unpredictable performance and internal | |||
damage. Extrapolation of test data from pumped-flow conditions to blowdown | |||
conditions may not be sufficient to ensure that a gate valve can operate under | |||
its design-basis conditions. | |||
Valve aging conditions can influence gate valve performance. The thrust | |||
requirements to operate gate valves under normal flow conditions can increase | |||
with time and valve stroking. | |||
Thrust requirements to unwedge gate valves under dynamic conditions may be | |||
greater than under static conditions. | |||
===Globe Valves=== | |||
Limited testing by EPRI of globe valves under blowdown or high-temperature | |||
flow conditions suggested that higher thrust than typically predicted may be | |||
required to operate these valves. | |||
Thrust requirements for globe valves are influenced by the area of the valve | |||
seat or guide. depending on the valve design. | |||
The EPRI test database is not sufficient to justify modifying the Limitorque | |||
guidelines for sizing and setting globe valves to lower the typical valve | |||
factor of 1.1 as-umed in the guidelines. | |||
k \- # | |||
IN 96-48 August 21, 1996 Butterfly Valves | |||
Several areas of the EPRI Butterfly Valve Application Guide need improvement | |||
or correction. EPRI is currently revising the application guide and plans to | |||
include new information on flow and torque coefficients; system analysis | |||
techniques; treatment of bearing, packing, and hub-seal torque: upstream elbow | |||
modeling: and rated and survivable torque calculations. | |||
2. MOV Key Failures | |||
The MOV key failures may involve a common-cause failure that could render | |||
redundant trains of certain safety-related systems inoperable if they had | |||
remained undetected. The MOV key failures can be attributed to (a)instal- lation and design deficiencies for anti-rotation keys, (b)loosening or | |||
slipping, wear or normal aging, excessive force or overtorque, and discre- pancies in material or size for valve operator-to-valve stem keys, and (c) | |||
high-impact loads, improper materials, installation deficiency, wear or normal | |||
aging, and vibration for motor pinion gear keys. | |||
The anti-rotation key failures involving installation deficiencies were | |||
of | generally associated with inadequate staking and securing of setscrews during | ||
instructions | installation of the keys. It appeared that the installation instructions | ||
provided by the vendors were not always included in licensee maintenance | provided by the vendors were not always included in licensee maintenance | ||
Line 634: | Line 333: | ||
procedures. | procedures. | ||
Many motor pinion gear key failures involving | Many motor pinion gear key failures involving an installation deficiency were | ||
an installation | |||
deficiency | |||
were | |||
due to failure to stake the keys following replacement of the motors or the | |||
pinion gears. Although licensees revised their MOV maintenance procedures to | |||
include restaking the pinion key or motor shaft as recommended by Limitorque | |||
Maintenance Update 89-1 (Accession 9608120068), many licensees did not | |||
the | investigate the potential problems of maintenance activities that were | ||
conducted before their procedure changes. | |||
The motor pinion gear key failures attributable to high-impact loads or | |||
improper material appear to involve AISI (American Iron and Steel Institute) | |||
type 1018 keys in high-speed and high-inertia configurations. The replacement | |||
the | of 1018 keys with harder 4140 keys in some cases may lead to keyway deforma- tion or damage, depending on impact loads and the shaft material. The situa- tion may present a complex stress problem that is not completely considered in | ||
design and could produce a severe and complex stress concentration on the key, as well as the keyway. This situation could lead to cracking and failure of | |||
the shaft. | |||
The potential for these key problems to render safety systems inoperable empa- sizes (a)the importance of plant maintenance programs in assuring that MOV | |||
keys are staked and secured as required, (b)the importance of plant MOV | |||
surveillance and maintenance activities in the early detection of key | |||
IN 96-48 August 21, 1996 degradation, and (c)the possibility of shaft cracking as a result of | |||
replacement of 1018 keys with harder material when the replacement will | |||
involve a relatively soft shaft and high impact loads. | |||
3. Limitorque Motor Actuator Performance | |||
The NRC staff conducted an inspection at Limitorque in May 1993 and reviewed | |||
the basis for its motor actuator sizing guidelines. As discussed in NRC | |||
the | Inspection Report 99900100/93-01. the staff found that the values for | ||
individual parameters assumed in the Limitorque sizing equation were not | |||
determined by testing but were founded primarily on engineering judgment. The | |||
lack of significant failure history of motor actuators when using the | |||
Limitorque sizing equation has been the primary basis for confidence in the | |||
equation. Licensee modifications of the parameters in the Limitorque sizing | |||
guidelines has the potential to influence performance. | |||
Tests of MOVs under differential pressure and flow conditions performed by | |||
licensees in response to GL 89-10 have revealed that significantly more torque | |||
and | and thrust are required to open and close many gate valves than predicted by | ||
the valve vendors. This need for more torque than originally believed has led | |||
licensees to evaluate the Limitorque motor actuator sizing guidelines to | |||
determine whether more torque output is available from the motor actuators | |||
than was predicted by the guidelines. The Limitorque sizing guidelines have | |||
assumed | typically been assumed to underestimate the output torque capability of motor | ||
actuators. Therefore, some licensees eliminate the application factor from | |||
the output torque equation and use run efficiency for ac-powered MOVs in the | |||
closing direction. Further, some licensees have asserted that motor torque | |||
greater than the nominal start rating may be assumed in the sizing guidelines | |||
because motors typically deliver more torque than their rating before they | |||
stall. | |||
In response to the questions surrounding the Limitorque sizing equation, the | |||
NRC Office of Nuclear Regulatory Research evaluated the performance of | |||
Limitorque motor actuators through testing at the Idaho ational Engineering | |||
Laboratory (INEL). Preliminary results of the INEL tests suggest that (1) | |||
motor output is greater than the nominal rating for many motors. (2)the | |||
actual output efficiency may not reach "run" efficiency for some Limitorque | |||
actuators and may drop below "pullout" efficiency under high loads, (3) the | |||
torque loss under degraded voltage conditions can be more severe for some ac | |||
motors than the typically assumed square of the ratio of actual voltage to | |||
rated voltage, and (4)the torque loss under degraded voltage conditions can | |||
be more severe for some dc motors than the typically assumed linear ratio. | |||
Preliminary results of this testing are documented in NUREG/CR-6100. "Gate | |||
Valve and Motor-Operator Research Findings" (September 1995). INEL is | |||
preparing a report. NUREG/CR-6478, to document its recent findings in this | |||
area. This report is scheduled to be issued by the end of 1996. | |||
IN 96-48 August 21, 1996 At meetings of the Motor-Operated Valve Users' Group of nuclear power plant | |||
licensees in February and July 1995, Commonwealth Edison (ComEd) presented the | |||
results of its motor and actuator output testing program. The testing | |||
conducted by ComEd was more extensive than the NRC-sponsored testing and | |||
of | revealed similar results. Previously, in NUREG/CP-0137, "Proceedings of the | ||
Third NRC/ASME Symposium on Valve and Pump Testing" (July 1994), motor | |||
actuator testing by Texas Utilities raised questions regarding Limitorque | |||
motor actuator output. Texas Utilities also found lower output during in situ | |||
motor actuator testing compared to torque stand testing. | |||
This information raises concerns regarding the basis for Limitorque acceptance | |||
of licensee assumptions that the torque output of its actuators is greater | |||
the | than predicted by the original Limitorque SEL guidelines. The NRC staff has | ||
between guidance relaxing the | been discussing with Limitorque the discrepancy between guidance relaxing the | ||
original motor actuator sizing criteria and the recent motor actuator test | |||
for the | results. The manufacturer has stated that updated information for the | ||
is being developed. | industry on the sizing of its motor actuators is being developed. | ||
===Related Generic Communications=== | ===Related Generic Communications=== | ||
* NRC IN 81-08. "Repetitive | * NRC IN 81-08. "Repetitive Failures of Limitorque Operator SMB-4 Motor-to-Shaft Key," March 20, 1981 (Accession 8011040272). | ||
Failures of Limitorque | |||
Operator SMB-4 Motor-to-Shaft | |||
Key," March 20, 1981 (Accession | |||
8011040272). | |||
* NRC IN 88-84. "Defective Motor Shaft Keys in Limitorque Motor | |||
Actuators." October 20, 1988 (Accession 8810140018). | |||
Valve | * NRC GL 89-10, "Safety-Related Motor-Operated Valve Testing and | ||
Surveillance," June 28, 1989 (Accession 8906290082). | |||
* NRC IN 90-37. "Sheared Pinion Gear-to-Shaft Keys in Limitorque Motor | |||
Actuators," May 24, 1990 (Accession 9005180095). | |||
* NRC IN | * NRC IN 90-40, "Results of NRC-Sponsored Testing of Motor-Operated | ||
Valves," June 5, 1990 (Accession 9005290270). | |||
* NRC IN 93-42, "Failure of Anti-Rotation Keys in Motor-Operated Valves | |||
Manufactured by Velan," June 9. 1993 (Accession 9306030147). | |||
* NRC IN 93-88. "Status of Motor-Operated Valve Performance Prediction | |||
Program by the Electric Power Research Institute," November 30, 1993 (Accession 93111904527!. | |||
* NRC IN 94-10, "Failures of Motor-Operated Valve Electric Power Train Due | |||
to Sheared or Dislodged Motor Pinion Gear Key," February 4. 1994 (Accession 9402010052). | |||
of Torque | IN 96-48 August 21, 1996 * NRC IN 94-69. "Potential Inadequacies in the Prediction of Torque | ||
for and Torque Output of Motor-Operated | Requirements for and Torque Output of Motor-Operated Butterfly Valves," | ||
September 28. 1994 (Accession 9409210211). | |||
This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
one of the technical contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
'. Thomas T. Martin, Director | |||
Division of Reactor Program Management | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu. AEOD | |||
(301) 415-2794 (301) 415-6356 Email: tgs@nrc.gov Email: cchl@nrc.gov | |||
Michael T. Bugg, RIII | |||
(630) 829-9500 | |||
Email: mtb@nrc.gov | |||
Attachment: List of Recently Issued NRC Information Notices | |||
A/; >'/c> | |||
K>,0 | |||
Attachment | |||
IN 96-48 August 21. 1996 LIST OF RECENTLY ISSUED | |||
NRC INFORMATION NOTICES | |||
Information Date of | |||
Notice No. Subject Issuance Issued to | |||
96-47 Recordkeeping, Decommis- 08/19/96 All U.S. Nuclear Regulatory | |||
sioning Notifications for Commission licensees | |||
Disposals of Radioactive | |||
Waste by Land Burial | |||
Authorized Under Former | |||
10 CFR 20.304. 20.302. | |||
and Current 20.2002 | |||
96-46 Zinc Plating of Hardened 08/12/96 All holders of OLs or CPs | |||
Metal Parts and Removal for nuclear power reactors | |||
of Protective Coatings | |||
in Refurbished Circuit | |||
Breakers | |||
96-45 Potential Common-Mode 8/12/96 All holders of OLs or CPs | |||
Post-Accident Failure of for nuclear power reactors | |||
Containment Coolers | |||
96-44 Failure of Reactor 8/05/96 All holders of OLs or CPs | |||
Trip Breaker from Cracking for nuclear power reactors | |||
of Phenolic Material in | |||
secondary contact assembly | |||
96-43 Failures of General 08/02/96 All holders of OLs or CPs | |||
Electric Magne-Blast for nuclear power reactors | |||
Circuit Breakers | |||
96-42 Unexpected Opening of 08/05/96 All holders of OLs or CPs | |||
Multiple Safety Relief for nuclear power reactors | |||
Valves | |||
96-41 Effects of a Decrease in 07/26/96 All holders of OLs or CPs | |||
water | Feedwater Temperature on for pressurized water | ||
Nuclear Instrumentation reactors | |||
96-40 Deficiencies in Material 07/25/96 All holders of OLs or CPs | |||
Dedication and Procurement for nuclear power reactors | |||
Practices and in Audits of | |||
Vendors | |||
OL = Operating License | |||
CP = Construction Permit | |||
IN 96-48 August 21, 1996 * NRC IN 94-69. "Potential Inadequacies in the Prediction of Torque | |||
Valves," September | Requirements for and Torque Output of Motor-Operated Butterfly Valves," | ||
September 28, 1994 (Accession 9409210211). | |||
This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
one of the technical contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
'Itiinal signed byBrian K Gimes | |||
41116A-Thomas T. Martin. Director | |||
I Division of Reactor Program Management | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu, AEOD | |||
(301) 415-2794 (301) 415-6356 Email: tgs@nrc.gov Email: cchl@nrc.gov | |||
Michael T. Bugg. RIII | |||
(630) 829-9500 | |||
Email: mtb@nrc.gov | |||
Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
DOCUMENT NAME: 96-48.IN | |||
To rpecefe a rrw of this document. Indicate In the box: "C" = Copy without enclosures "" WCopy Ores No copy | |||
=N"- | |||
OFFICE PUB:ADM I D/DE I C/PECB:DRPM I ID | |||
INAME BCalure* BSheron* AChaffee* J11M0rtin | |||
DATE 06/21/96 07/16/96 08/13/96 1 08//5n6 OFFICIAL RECORD COPY | |||
IN 96-XX | |||
August XX. 1996 This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
one of the technical contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Brian K. Grimes. Acting Director | |||
Division of Reactor Program Management | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu, AEOD | |||
(301) 415-2794 (301) 415-6356 Internet:tgs@nrc.gov Internet:cchl@nrc.gov | |||
Michael T. Bugg. NRR | |||
(630) 829-9500 | |||
Internet:mtb@nrc.gov | |||
Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
Attachment: | Attachment: List of Recently Issued NRC Information Notices | ||
List of Recently Issued NRC Information | |||
DOCUMENT NAME: G:\TAG\MOV96.IN5 Ta rgeAve a coov of this document. Indicate In the box: "C"a Copy without enclosures r - Copy with enclosures "N"z No copy | |||
OFFICE PUB:ADM -I D/DE I IC/PECB:DRPM; l D/DRPM | |||
NAME BCalure* BSheronI ACha ffee VI BGrimes | |||
DATE 06/21/96 08/ /96 08/1';/96 - 08/ /96 OFFICIAL v r | |||
PA f) | |||
-,r ' '.- | |||
IN 96-XX | |||
in the Prediction | July XX, 1996 * NRC IN 94-69, Potential Inadequacies in the Prediction of Torque | ||
of | Requirements for and Torque Output of Motor-Operated Butterfly Valves,w | ||
September 28, 1994. | |||
This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
one of the technical contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Brian K. Grimes, Acting Director | |||
Division of Reactor Program Management | |||
Office of Nuclear Reactor Regulation | |||
contacts | Technical contacts: Thomas G. Scarbrough, NRR | ||
(301) 415-2794 Internet:tgs~nrc.gov | |||
Michael T. Bugg, NRR | |||
(301) 415-3303 Internet:mxbSnrc.gov | |||
Chuck Hsu, AEOD | |||
(301) 415-6356 Internet:cchl@nrc.gov | |||
Attachment: | Attachment: List of Recently Issued NRC Information Notices | ||
List of Recently Issued NRC Information | |||
*SEE PREVIOUS CONCURRENCE | |||
Afttthmontn | Afttthmontn lit nf Pargnt1v TtvIs d NRC Informatinn Notices | ||
OFFICE PUB:ADM D/ I 1&( \ C/PECB:DRPM D/DRPM | |||
NAME BCalure* BS AChaffee BGrimes | |||
DATE 06/21/96 j /&/96 / /96 [/ /96 (OFFICIAL RECORD COPY] $1 DOCUMENT NAME: G:\TAG\MOV96.INt | |||
Chuck Hsu, AEOD | |||
(301) 415-6356 Internet:cchlnrc.gov | |||
Attachment: | Attachment: List of Recently Issued NRC Information Notices | ||
List of Recently Issued NRC Information | |||
OFFICE PUB:ADM C/E14EB:DE C/PECB:DRPM D/DRPM | |||
NAME Tech RWessman AChaffee BGrimes | |||
DATE C /LV//96 no /96 / /96 1 /96 | |||
[OFFICIAL RECORD COPY] | |||
DOCUMENT NAME: G:\TAG\MOV96.IN | |||
I | |||
9/}} | |||
{{Information notice-Nav}} | {{Information notice-Nav}} |
Latest revision as of 04:37, 24 November 2019
l
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 August 21, 1996 NRC INFORMATION NOTICE 96-48: MOTOR-OPERATED VALVE PERFORMANCE ISSUES
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to (1) lessons learned from the Electric Power
Research Institute (EPRI) Motor-Operated Valve (MOV) Performance Prediction
Program, (2)performance problems with MOV key failures described in a recent
NRC Office for Analysis and Evaluation of Operational Data (AEOD) study, and
(3)the potential for torque output from MOV actuators to be less than
predicted by Limitorque Corporation. 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 are not NRC requirements; therefore, no
specific action or written response is required.
Background
In the 1980s. continuing problems with the performance of MOVs at nuclear
power plants raised concerns regarding MOV design, testing, and maintenance.
In response to these problems, both the nuclear industry and NRC initiated
efforts to improve the performance of MOVs at nuclear plants. In 1989, the
NRC staff issued Generic Letter (GL) 89-10, "Safety-Related Motor-Operated
Valve Testing and Surveillance," requesting that nuclear power plant licensees
and construction permit holders verify the design-basis capability of their
safety-related MOVs. In response to GL 89-10, the nuclear industry has
studied the performance of MOVs through testing and analyses. As a result of
these activities, some weaknesses in the design and manufacture of MOVs were
discovered through evaluation of the performance history of MOVs. In this
information notice, the staff discusses three issues involving MOV performance
that have been identified.
Description of Circumstances
1. Lessons Learned from EPRI MOV Performance Prediction Program
As part of the industry effort regarding the MOV issue. EPRI initiated an MOV
Performance Prediction Program to develop a methodology to be used by
licensees in demonstrating the design-basis capability of MOVs when valve- specific design-basis test data are not available. The program included
9608150028 I
PX 4\\\s 1-Dv-11C/if
IN 96-48 August 21, 1996 development of improved methods for prediction or evaluation of system flow
parameters; gate, globe, and butterfly valve performance: and motor actuator
rate-of-loading effects (load-sensitive behavior). Further, EPRI performed
testing to provide information for refining the gate valve model and rate-of- loading methods and conducted numerous MOV tests to provide data for model and
method development and validation, including flow loop testing, parametric
flow loop testing of butterfly valve disk designs, and in situ MOV testing.
In November 1994, the Nuclear Energy Institute (NEI) submitted the proprietary
EPRI Topical Report TR-103237, "EPRI MOV Performance Prediction Program -
Topical Report," for review by the NRC staff. EPRI prepared 25 additional
reports to support the topical report. On March 15, 1996, the NRC staff
issued a Safety Evaluation (SE) documenting the staff review of the topical
report. With the conditions and limitations described in the SE, the staff
stated that the EPRI program provides an acceptable methodology to predict the
thrust or torque required to operate gate, globe, and butterfly valves within
the scope of the EPRI program and to bound the effects of load-sensitive
behavior on motor actuator thrust output.
In a letter dated September 27, 1995, NEI forwarded a summary of important
contributions and findings resulting from the EPRI MOV Performance Prediction
Program. As described in an enclosure to the NEI letter, important findings
(or confirmatory information) from the EPRI MOV program include the following:
a. The traditional methods for predicting gate valve performance might be
nonconservative for many applications because of incomplete equations.
design features, manufacturing controls, and wide-ranging friction
coefficients.
b. The edge radii on disk seats and guide slots are critical to gate valve
performance and predictability.
c. Stellite friction coefficients increase with differential-pressure valve
strokes in cold water to a plateau level, stabilize quickly in hot
water, and decrease as differential pressure increases.
d. Gate valves with carbon steel guides and disk guide slots with tight
clearances might fail to close under blowdown conditions.
e. Many existing gate valve manufacturing and design processes and
controls, and plant maintenance practices, might contribute to poor
valve performance.
f. Traditional methods for predicting globe valve performance for
incompressible flow conditions are nonconservative for globe valves in
which differential pressure acts across the plug guide.
' IN 96-48 August 21. 1996 g. Globe valve thrust requirements for some designs can be excessive under
compressible flow and blowdown conditions because of the potential for
plug-side loading.
h. Rate-of-loading effects (load-sensitive behavior) can reduce the static
thrust output by up to 30 percent under dynamic conditions.
i. Hydrodynamic torque coefficients used by some butterfly valve
manufacturers might be nonconservative for certain applications, with
valves located near piping elbows especially vulnerable.
j. Butterfly valve seats should be periodically replaced to avoid hardening
or degradation.
In addition to these reported important findings, EPRI confirmed that thrust
requirements to unwedge a gate valve can be higher under dynamic conditions
than under static conditions.
2. MOV Key Failures
On March 29. 1996. AEOD issued report AEOD/E96-01. entitled, "Engineering
Evaluation - Motor-Operated Valve Key Failures," on the continuing occurrence
of problems with keys in MOVs at nuclear power plants. A significant number
of MOV key failures have been identified that involved (a)anti-rotation keys.
(b)valve operator-to-valve stem keys. and (c)motor pinion gear keys. A
total of 73 reports were written involving MOV key failures between January
1990 through September 1995. Many of these key failures were not detected
during surveillance tests but were detected on demand, during valve
operations. or during maintenance activities and had existed for some time
before they were discovered. A number of key failures were discovered during
maintenance activities even though the valves had been operated satisfactorily
and passed all previous surveillance tests.
3. Limitorque Motor Actuator Performance
In 1977. Limitorque Corporation established guidelines (referred to as the SEL
documents) for sizing ac-powered motor actuators used in MOVs. Those
guidelines predicted the motor actuator output torque as a product of the
nominal motor-rated start torque. pullout efficiency, application factor
(typically 0.9), overall actuator gear ratio, and a degraded voltage factor.
Over the past few years, Limitorque has accepted the use of run efficiency for
closing valves powered by ac-powered motor actuators. Limitorque has also
stated that licensees may eliminate the application factor when voltage
supplied to the motor is less than 90 percent of its rated voltage. (See
Limitorque Technical Update 93-03 [Accession 9608120083].) Recent industry
IN 96-48 August 21. 1996 and NRC-sponsored test information has raised questions regarding the accuracy
of the Limitorque assumptions for actuator efficiency.
Discussion
1. Lessons Learned from the EPRI MOV Performance Prediction Program
As discussed in the staff SE on the EPRI topical report, the EPRI program
provided important information on the design, testing. and maintenance of MOVs
in nuclear power plants. Some of the EPRI information is applicable to gate.
globe, and butterfly valves regardless of the type of actuator operating the
valve. Examples of such information are given below:
Gate Valves
Almost all flow testing by licensees in response to GL 89-10 was conducted
under pumped-flow conditions. Several gate valves tested by EPRI under
blowdown conditions demonstrated unpredictable performance and internal
damage. Extrapolation of test data from pumped-flow conditions to blowdown
conditions may not be sufficient to ensure that a gate valve can operate under
its design-basis conditions.
Valve aging conditions can influence gate valve performance. The thrust
requirements to operate gate valves under normal flow conditions can increase
with time and valve stroking.
Thrust requirements to unwedge gate valves under dynamic conditions may be
greater than under static conditions.
Globe Valves
Limited testing by EPRI of globe valves under blowdown or high-temperature
flow conditions suggested that higher thrust than typically predicted may be
required to operate these valves.
Thrust requirements for globe valves are influenced by the area of the valve
seat or guide. depending on the valve design.
The EPRI test database is not sufficient to justify modifying the Limitorque
guidelines for sizing and setting globe valves to lower the typical valve
factor of 1.1 as-umed in the guidelines.
k \- #
IN 96-48 August 21, 1996 Butterfly Valves
Several areas of the EPRI Butterfly Valve Application Guide need improvement
or correction. EPRI is currently revising the application guide and plans to
include new information on flow and torque coefficients; system analysis
techniques; treatment of bearing, packing, and hub-seal torque: upstream elbow
modeling: and rated and survivable torque calculations.
2. MOV Key Failures
The MOV key failures may involve a common-cause failure that could render
redundant trains of certain safety-related systems inoperable if they had
remained undetected. The MOV key failures can be attributed to (a)instal- lation and design deficiencies for anti-rotation keys, (b)loosening or
slipping, wear or normal aging, excessive force or overtorque, and discre- pancies in material or size for valve operator-to-valve stem keys, and (c)
high-impact loads, improper materials, installation deficiency, wear or normal
aging, and vibration for motor pinion gear keys.
The anti-rotation key failures involving installation deficiencies were
generally associated with inadequate staking and securing of setscrews during
installation of the keys. It appeared that the installation instructions
provided by the vendors were not always included in licensee maintenance
procedures.
Many motor pinion gear key failures involving an installation deficiency were
due to failure to stake the keys following replacement of the motors or the
pinion gears. Although licensees revised their MOV maintenance procedures to
include restaking the pinion key or motor shaft as recommended by Limitorque
Maintenance Update 89-1 (Accession 9608120068), many licensees did not
investigate the potential problems of maintenance activities that were
conducted before their procedure changes.
The motor pinion gear key failures attributable to high-impact loads or
improper material appear to involve AISI (American Iron and Steel Institute)
type 1018 keys in high-speed and high-inertia configurations. The replacement
of 1018 keys with harder 4140 keys in some cases may lead to keyway deforma- tion or damage, depending on impact loads and the shaft material. The situa- tion may present a complex stress problem that is not completely considered in
design and could produce a severe and complex stress concentration on the key, as well as the keyway. This situation could lead to cracking and failure of
the shaft.
The potential for these key problems to render safety systems inoperable empa- sizes (a)the importance of plant maintenance programs in assuring that MOV
keys are staked and secured as required, (b)the importance of plant MOV
surveillance and maintenance activities in the early detection of key
IN 96-48 August 21, 1996 degradation, and (c)the possibility of shaft cracking as a result of
replacement of 1018 keys with harder material when the replacement will
involve a relatively soft shaft and high impact loads.
3. Limitorque Motor Actuator Performance
The NRC staff conducted an inspection at Limitorque in May 1993 and reviewed
the basis for its motor actuator sizing guidelines. As discussed in NRC
Inspection Report 99900100/93-01. the staff found that the values for
individual parameters assumed in the Limitorque sizing equation were not
determined by testing but were founded primarily on engineering judgment. The
lack of significant failure history of motor actuators when using the
Limitorque sizing equation has been the primary basis for confidence in the
equation. Licensee modifications of the parameters in the Limitorque sizing
guidelines has the potential to influence performance.
Tests of MOVs under differential pressure and flow conditions performed by
licensees in response to GL 89-10 have revealed that significantly more torque
and thrust are required to open and close many gate valves than predicted by
the valve vendors. This need for more torque than originally believed has led
licensees to evaluate the Limitorque motor actuator sizing guidelines to
determine whether more torque output is available from the motor actuators
than was predicted by the guidelines. The Limitorque sizing guidelines have
typically been assumed to underestimate the output torque capability of motor
actuators. Therefore, some licensees eliminate the application factor from
the output torque equation and use run efficiency for ac-powered MOVs in the
closing direction. Further, some licensees have asserted that motor torque
greater than the nominal start rating may be assumed in the sizing guidelines
because motors typically deliver more torque than their rating before they
stall.
In response to the questions surrounding the Limitorque sizing equation, the
NRC Office of Nuclear Regulatory Research evaluated the performance of
Limitorque motor actuators through testing at the Idaho ational Engineering
Laboratory (INEL). Preliminary results of the INEL tests suggest that (1)
motor output is greater than the nominal rating for many motors. (2)the
actual output efficiency may not reach "run" efficiency for some Limitorque
actuators and may drop below "pullout" efficiency under high loads, (3) the
torque loss under degraded voltage conditions can be more severe for some ac
motors than the typically assumed square of the ratio of actual voltage to
rated voltage, and (4)the torque loss under degraded voltage conditions can
be more severe for some dc motors than the typically assumed linear ratio.
Preliminary results of this testing are documented in NUREG/CR-6100. "Gate
Valve and Motor-Operator Research Findings" (September 1995). INEL is
preparing a report. NUREG/CR-6478, to document its recent findings in this
area. This report is scheduled to be issued by the end of 1996.
IN 96-48 August 21, 1996 At meetings of the Motor-Operated Valve Users' Group of nuclear power plant
licensees in February and July 1995, Commonwealth Edison (ComEd) presented the
results of its motor and actuator output testing program. The testing
conducted by ComEd was more extensive than the NRC-sponsored testing and
revealed similar results. Previously, in NUREG/CP-0137, "Proceedings of the
Third NRC/ASME Symposium on Valve and Pump Testing" (July 1994), motor
actuator testing by Texas Utilities raised questions regarding Limitorque
motor actuator output. Texas Utilities also found lower output during in situ
motor actuator testing compared to torque stand testing.
This information raises concerns regarding the basis for Limitorque acceptance
of licensee assumptions that the torque output of its actuators is greater
than predicted by the original Limitorque SEL guidelines. The NRC staff has
been discussing with Limitorque the discrepancy between guidance relaxing the
original motor actuator sizing criteria and the recent motor actuator test
results. The manufacturer has stated that updated information for the
industry on the sizing of its motor actuators is being developed.
Related Generic Communications
- NRC IN 81-08. "Repetitive Failures of Limitorque Operator SMB-4 Motor-to-Shaft Key," March 20, 1981 (Accession 8011040272).
- NRC IN 88-84. "Defective Motor Shaft Keys in Limitorque Motor
Actuators." October 20, 1988 (Accession 8810140018).
- NRC GL 89-10, "Safety-Related Motor-Operated Valve Testing and
Surveillance," June 28, 1989 (Accession 8906290082).
- NRC IN 90-37. "Sheared Pinion Gear-to-Shaft Keys in Limitorque Motor
Actuators," May 24, 1990 (Accession 9005180095).
- NRC IN 90-40, "Results of NRC-Sponsored Testing of Motor-Operated
Valves," June 5, 1990 (Accession 9005290270).
- NRC IN 93-42, "Failure of Anti-Rotation Keys in Motor-Operated Valves
Manufactured by Velan," June 9. 1993 (Accession 9306030147).
- NRC IN 93-88. "Status of Motor-Operated Valve Performance Prediction
Program by the Electric Power Research Institute," November 30, 1993 (Accession 93111904527!.
- NRC IN 94-10, "Failures of Motor-Operated Valve Electric Power Train Due
to Sheared or Dislodged Motor Pinion Gear Key," February 4. 1994 (Accession 9402010052).
IN 96-48 August 21, 1996 * NRC IN 94-69. "Potential Inadequacies in the Prediction of Torque
Requirements for and Torque Output of Motor-Operated Butterfly Valves,"
September 28. 1994 (Accession 9409210211).
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
'. Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu. AEOD
(301) 415-2794 (301) 415-6356 Email: tgs@nrc.gov Email: cchl@nrc.gov
Michael T. Bugg, RIII
(630) 829-9500
Email: mtb@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
A/; >'/c>
K>,0
Attachment
IN 96-48 August 21. 1996 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No. Subject Issuance Issued to
96-47 Recordkeeping, Decommis- 08/19/96 All U.S. Nuclear Regulatory
sioning Notifications for Commission licensees
Disposals of Radioactive
Waste by Land Burial
Authorized Under Former
10 CFR 20.304. 20.302.
and Current 20.2002
96-46 Zinc Plating of Hardened 08/12/96 All holders of OLs or CPs
Metal Parts and Removal for nuclear power reactors
of Protective Coatings
in Refurbished Circuit
Breakers
96-45 Potential Common-Mode 8/12/96 All holders of OLs or CPs
Post-Accident Failure of for nuclear power reactors
Containment Coolers
96-44 Failure of Reactor 8/05/96 All holders of OLs or CPs
Trip Breaker from Cracking for nuclear power reactors
of Phenolic Material in
secondary contact assembly
96-43 Failures of General 08/02/96 All holders of OLs or CPs
Electric Magne-Blast for nuclear power reactors
Circuit Breakers
96-42 Unexpected Opening of 08/05/96 All holders of OLs or CPs
Multiple Safety Relief for nuclear power reactors
Valves
96-41 Effects of a Decrease in 07/26/96 All holders of OLs or CPs
Feedwater Temperature on for pressurized water
Nuclear Instrumentation reactors
96-40 Deficiencies in Material 07/25/96 All holders of OLs or CPs
Dedication and Procurement for nuclear power reactors
Practices and in Audits of
Vendors
OL = Operating License
CP = Construction Permit
IN 96-48 August 21, 1996 * NRC IN 94-69. "Potential Inadequacies in the Prediction of Torque
Requirements for and Torque Output of Motor-Operated Butterfly Valves,"
September 28, 1994 (Accession 9409210211).
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
'Itiinal signed byBrian K Gimes
41116A-Thomas T. Martin. Director
I Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu, AEOD
(301) 415-2794 (301) 415-6356 Email: tgs@nrc.gov Email: cchl@nrc.gov
Michael T. Bugg. RIII
(630) 829-9500
Email: mtb@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
DOCUMENT NAME: 96-48.IN
To rpecefe a rrw of this document. Indicate In the box: "C" = Copy without enclosures "" WCopy Ores No copy
=N"-
OFFICE PUB:ADM I D/DE I C/PECB:DRPM I ID
INAME BCalure* BSheron* AChaffee* J11M0rtin
DATE 06/21/96 07/16/96 08/13/96 1 08//5n6 OFFICIAL RECORD COPY
IN 96-XX
August XX. 1996 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes. Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu, AEOD
(301) 415-2794 (301) 415-6356 Internet:tgs@nrc.gov Internet:cchl@nrc.gov
Michael T. Bugg. NRR
(630) 829-9500
Internet:mtb@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
Attachment: List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\TAG\MOV96.IN5 Ta rgeAve a coov of this document. Indicate In the box: "C"a Copy without enclosures r - Copy with enclosures "N"z No copy
OFFICE PUB:ADM -I D/DE I IC/PECB:DRPM; l D/DRPM
NAME BCalure* BSheronI ACha ffee VI BGrimes
DATE 06/21/96 08/ /96 08/1';/96 - 08/ /96 OFFICIAL v r
PA f)
-,r ' '.-
IN 96-XX
July XX, 1996 * NRC IN 94-69, Potential Inadequacies in the Prediction of Torque
Requirements for and Torque Output of Motor-Operated Butterfly Valves,w
September 28, 1994.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Thomas G. Scarbrough, NRR
(301) 415-2794 Internet:tgs~nrc.gov
Michael T. Bugg, NRR
(301) 415-3303 Internet:mxbSnrc.gov
Chuck Hsu, AEOD
(301) 415-6356 Internet:cchl@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
Afttthmontn lit nf Pargnt1v TtvIs d NRC Informatinn Notices
OFFICE PUB:ADM D/ I 1&( \ C/PECB:DRPM D/DRPM
NAME BCalure* BS AChaffee BGrimes
DATE 06/21/96 j /&/96 / /96 [/ /96 (OFFICIAL RECORD COPY] $1 DOCUMENT NAME: G:\TAG\MOV96.INt
Chuck Hsu, AEOD
(301) 415-6356 Internet:cchlnrc.gov
Attachment: List of Recently Issued NRC Information Notices
OFFICE PUB:ADM C/E14EB:DE C/PECB:DRPM D/DRPM
NAME Tech RWessman AChaffee BGrimes
DATE C /LV//96 no /96 / /96 1 /96
[OFFICIAL RECORD COPY]
DOCUMENT NAME: G:\TAG\MOV96.IN
I
9/