ML20237D056
| ML20237D056 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 12/31/1987 |
| From: | PORTLAND GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20237D052 | List: |
| References | |
| IEB-85-003, IEB-85-3, NUDOCS 8712230016 | |
| Download: ML20237D056 (79) | |
Text
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t TROJAN NUCLEAR PLANT
SUMMARY
REPORT OF THE1 SAFETY-RELATED MOTOR-OPERATED VALVE SWITCH SETTING REVIEW AND TESTING PROGRAM (IN RESPONSE TO.IE BULLETIN 85-03)
DECEMBER 1987 A
TROJAN NUCLEAR PLANT
SUMMARY
REPORT OF SAFETY-RELATED MOTOR-OPERATED VALVE SWITCH SETTING REVIEW AND TESTING PROGRAM FOR TROJAN NUCLEAR PLANT CONTENTS Section Title Page
1.0 INTRODUCTION
1-1 2.0 PROGRAM DESCRIPTION 2-1 2.1 Valve Testing Program 2-1 2.2 Data Confirmation 2-5 2.3 Differential Pressure Testing 2-6 2.4 Configuration Confirmation 2-8 2.5 Switch Setting Procedures 2-9 3.0 TEST PROGRAM RESULTS AND ANALYSIS 3-1 3.1 Valve Data Summary 3-1 3.2 Review of Valve Problems Encountered 3-2 3.3 Report of Findings 3-11
4.0 CONCLUSION
S 4-1 4.1 Switch Settings 4-1 4.2 Current Programs 4-2 Appendix A
Thrust Requirement Calculations A-1 i
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1.0 INTRODUCTION
On November 15, 1985, the Nuclear Regulatory Commission (NRC) Office of Inspection and Enforcement (IE) issued IE Bulletin 85-03:
" Motor-Operated Valve Common Mode Failures During= Plant Transients Due to Improper Switch Settings".
The purpose of the Bulletin was to " request licensees to
' develop and implement a program to ensure that switch settings on certain safety-related motor-operated valves are selected, set, and maintained-correctly to accommodate the maximum differential pressures expected on these valves during both normal and abnormal events within the design basis".
IE Bulletin 85-03 calls for six action items to be addressed for motor-operated valves in the high-pressure coolant injection and emergency (or auxiliary) feedwater systems that are required to be tested for opera-tional readiness, in accordance with Title 10 Code of Federal Regulations
-(CFR) 50.55a(g). The valves were further selected on the basis of the Westinghouse Owners Group Safety-Related Motor-Operated Valve (MOV)
Program issued in April 1986.
High' Pressure Coolant Injection (HPCI), as defined by the generic Westinghouse Owners Croup methodology, includes those portions of the Chemical and Volume Control System (CVCS), through the centrifugal charging pumps (CCPs) and the Boron Injection Tank (BIT), and the Safety Injection (SI) System, that are required to function in order to estab-lish a flow path from the refueling water storage tank (RWST) to the Reactor Coolant System (RCS) during the injection phase af ter a Design Basis Accident. This excludes the accumulators and the Residual Heat Removal (RHR) System, as well as Containment sump recirculation after depletion of the RWST contents.
Although the SI System is not considered a high pressure injection system at Trojan, it is included here for conservatism.
Systems and components involved in the RCS cooldown after high pressure injection are not included in the IE Bulletin 85-03 scope of work.
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An interim " Report on Safety-Related Motor-Operated Valve Switch Setting Review and Testing Program for Trojan Nuclear Plant" was submitted on l
July 15, 1986 to complete the first action item, a review of the valve design bases, and maximum valve pressure drops, as well as outline a j
program to complete the remaining items, as required by the Bulletin.
This Summary Report is submitted in response to the final action item and I
completes the response to IE Bulletin 85-03.
The following sections describe the program pursued to review and revise switch settings, describe the valve testing to verify the new settings, and describes the testing and maintenance.
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-4 2.0 PROGRAM DESCRIPTION 2.1 VALVE TESTING PROGRAM The principal test used to determine adequacy of MOV switch settings was performed by the Motor-operated Valve Analysis and Test System (MOVATS).
While MOVATS provided most of the test information on switch settings for the Bulletin work reported on here, it is not the only test used to assure operability of safety-related, motor-operated valves at Trojan.
~ Maintenance and operating tests were performed as well.
The valve test program is described below.
2.1.1' MOVATS TESTING MOVATS is a portable testing device designed to monitor motor-operated valve performance in the field. The system acquires, stores, and per-forms calculations on instantaneous readings of the following valve motor operator characteristics during a valve cycle:
(1) Axial motion of the worm.
(2) Actuation of the torque and limit switches.
(3) Motor current.
MOVATS provides three signature traces which can be utilized in analyzing the condition of motor-operated valves. These are:
(1) Stem thrust signature.
(2) Control switch signature.
(3) Motor current signature.
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Stem Thrust Signature J
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Stem thrust can be measured by mcnitoring the instantaneous axial moveh>\\ ]
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v ment of the worm. To obtain a reading of worm axial motion, a linear variable differential transformer was used in a device developed by MOVATS called a thrust measuring device (TMD).
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To install the TMD on the motor operator, the spring-pack dust cover is removed, and the TMD is mounted such that its plunger comes in contact with the preload nut.
With the TMD installed, any movement of the spring pack or worm will be translated into a voltage output of the TKD.
i In order tc " characterize" the spring-pack movement, a calibrated load
.y cell was mounted on the valve. With the TMD installed and monitoring spring-packposition,thevalveisopenedelbctrically.
After the valve stem contacts the load cell, the stem load riseAtwith a correspooling 1
spring-pack movement.
The spring-pack movement signature can then,be directly correlated to the actual load signature. The slope of the resultant curve, which is referred to as the K-factor of the spring pack and is represented in terms of pounds of stem thrust per unit of Spring-pack deflection, or unit of torque switch setting.
Control Switch Signature s
I By means of a epecially designed multicoil" transformer device, a single f4 signature was generated that gives the exact times during the valvo cycle that the torque and limit switches actuate.
By superimposing this signa-ture on the thrust signature, the exact points sud loading conditions at which the various switches actuate are doi,nemined.
Motor Current Signature A " clamp-on" ammeter, with analog output, was utilized to produce this signature. Changes in the motor current signatures can provide periodic q
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indication of MOV condition which can be trended to provide indication of valve / operator degradation.
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2.1.2 MAIMEN'ANgy. INCJ EIMIdN, AND TESVNG
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All valves in safety-related systems in,the Trojan Plant are subject to an extensive maintenance tp ting pro pam. An important part of this programistheservicingperformeddudn;theannualrefuelingoutage.7 Each valve is serviced once every threu' years.
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i This servicing includes inspection for parts degradation, replacement nd wornordamagedparts,androut{7.-teststocheckthevalidityofswitch and breaker sg' tings.
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,p The methods and pro 3edures used in' this program are described in Trojan
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maintenance proceiures.
<Jm 2.1.3 OPERATING TESTS 5
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The basis for operational testing (hf ' safety.r'yl.ated valves is the j '.Lmericar)(ociety of Hechanical Engineers (A.S$E) Boiler and Pressure Vessel dpfe, Section,XI. The specifi s of the current program atet dolpiler) in Poral'ahd General Electrki(PGE) Topical Report PGE-1048,
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"Tro.jan' Bucleiic.Vlsant Pump and 'Jsl've Inservice Testing Program Second g,'
i 10-Yies1 Interval".
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l Required tests and test frequency are assigned to each valw to meet the p
4 requiren>ents 'of the <nservice Inspectiorp yde. Specific tects and test frequency are spelled cut in the refercried copical EepotN.4 l
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2.1.4 VALVES TESTED
'l Du-(i1 The motor-operatei (ho),lhigh-pressure injection system valves included within the. scope of the tlesting progten ara 'as follows:
f" Valv$ No..
Service MO 8806 Gli Pump Suction sf s
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MO 8923A&B SI Pump Suction l
MO 8821A&B SI Pump Discharge to Cold Geg MO 8835 SI Pump Discharge to Cold Leg 110 112D&E CCP Suction from RWST
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MO 8106 CCP Normal Charging to Cold Leg
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MO 8105
.CCP Normal Charging to Cold Leg MO 860545B. ",
CCP Discharge through BIT MO 880ltGB
'CCP Discharge through BIT MO 112B40 CCP Suction from Volume Control Tank (VCT)
MO 8111
' CC?.Minira Recirculation MO 811R CCP Miniaum Recirculation MO 8814 DI Pump. Minimum Recirculation MO 8813 SI Pitmp Minimum Recirculation q.
The Auxillu'y Feodwater (AFW) System providas a reliable source of feed-watee. to t.pt steam generators in the event that main feedwater flow is
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lost. 'Tny' motor-operated 'rulves, including control valves (CVs) reviewed j
included all these'vesociated,yith establishing a riow path from a water coarce to the.stedm genetetors, as well as the valmts related to assure
. propt r operation of systoia corptrnents. The following valves were
'nwhided:
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Valve No.
Service
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MO 3060B Servier Water to Drive Coolers MO 3045A&B forvive,Wsher to AFW Pump Suction j
CV 3')OMA1 AFW PrAp Dircharge Control 1
CV 3004A2 AFW Pump Discharge Contect CV 3004B1 AFW Pump Discivarge Controi CV 3004D2 AFW Pump Discharge Control L
CV 3004Cl AFW Pump Discharge Control i
CV 3034C2 AFW Pump Discharge Control
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CV'3004D1 AFW Pump Discharge Controi l
CV 3004D2 AFW Pump Discharge Control l
MO 30;l Turbine Drivec Trip and Throttle l
l MO 317/!,
Turbine Drivar Steam Inlet MG 2947thB Motor-Driven AFW Pump Discharge Control 19 2-4 1
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2.2 DATA CONFIRMATION One of the first steps taken in the test program was to confirm present valve / operator configuration and design basis. This process is described below.
i The manufacturers of each of the 35 valves in the test sample were requested to furnish or confirm data pertaining to each valve.
The information was supplied on a standard data sheet.
The principal data included:
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(1) Valve stem thrust required to actuate the valve at the current design basis differential pressure.
(2) Maximum allowable stem thrust which will not cause damage to valve parts.
After receipt of the valve manufacturer's completed data sheets, they were sent to the motor operator vendor for their use in evaluating the thrust / torque required by the valve and the ability of the operator to meet this requirement, and to provide the proper torque switch settings.
The principal motor operator data included:
(1) The torque switch setting which will allow the operator to develop the thrust required to actuate the valve at design i
basis differential pressure before reaching the torque switch cutoff point.
j (2) Limiter plate setting to preclude damage to the valve and/or its operator.
Other data provided for the motor, gearing and spring pack were used to confirm configuration, j
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b After completion of the review of current maximum differential pressures for each valve in the test program, reported initially to the NRC on
-July 16, 1986, a review of design documents, such as drawings, data l
sheets, valve specifications, and line tables, was conducted to identify l
any inconsistencies between the current design basis differential
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pressures' adopted for this study and the presently installed equipment.
The comparison of current differential pressures with originally selected 1
differential pressures, on which the as-built design was based, revealed that there were no discrepancies that would necessitate equipment changes.
It was confirmed that all operators had design capacity to actuate the. valves on which they were installed at design basis differential pressure.
2.3 DIFFERENTIAL PRESSURE TESTING In development of the test plan'to respond to IE Bulletin 85-03, it was determined that testing all valves at maximum differential pressure was not practical. A decision on which valves would be tested in this manner was required and all valves in the scope of the Bulletin were evaluated.
Wedge-type gates are torque seated valves that have unique friction.
characteristics on seating and unseating, including pullout in the opening direction. This makes them the most likely candidates for maximum differential pressure testing.
Globe valves are also torque seated valves. These valves open and close in line with flow and differential pressure.
Resistance to closure and/or opening is much more readily defined than are the frictional forces perpendicular to flow and differential pressure for gate valves.
Quarter turn valves, such as the butterfly valve MO 3060B, are opened and closed by limit switches. The torque switch serves only as backup, and torque requirements are determined by disc / seal interaction, not by flow or differential pressure.
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Information from MOVATS, and other utilities' test. programs, demonstrate that standard-sizing and torque switch setting formulas could be used for
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.most gate;and globe valves.
Full flow differential pressure testing was.
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done for two gate valves, MO 8801A&B, and two globe valves, MO 8110 and l
MO 8111.
These valves were selected for the following reasons:
(1) :These valves have the highest differential pressure in the test sample.
(2) MO 8801A&B are wedge gate valves, a type of valve which some plants have determined require higher than calculated seating force.
.( 3 ) Full flow and head tests were required due to major maintenance work done to the CCPs during the outage.
MO 8801A&B were opened and closed under design basis differential pressure' conditions with satisfactory results, thus providing PGE with the confidence that the standard sizing formulas' identified in Appendix A 1
are suitable and satisfactory for establishing the required thrust values for the remainder of the wedge gate valves in.the test sample.
The CCP minimum flow recirculation valves, MO 8110 and MO 8111, 2-inch l
globe valves, were also tested under full flow and head conditions.
They, too, were opened and closed at design basis differential pressure with satisfactory results, which demonstrates that conventional methods of calculating required thrust for globe valves are acceptable.
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All of the other valves in the test sample were tested at zero differential pressure.
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'2. 4 CONFIGURATION CONFIRMATION
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g An important aspect of this program is verification of the configuration of the motor-operated valves presently installed at Trojan.
Inadvertent-substitution of different operator, or operator parts, for those originally supplied, or later installed in accordance with controlled procedures, could invalidate calculations based on information on valve / operator characteristics supplied by the manufacturers of these components.
The most important aspect of configuration confirmation is the verifica-tion of nameplate data. The MOVATS testing program standard requires recording of most of the operator and motor nameplate data and the valve plant identification number.
In every case, the nameplate data recorded at Trojan was in agreement with that furnished by the manufacturers on the as-shipped configuration.
The possibility of operator. internal reconfiguration was also considered, using a method adopted at the Rancho Seco Nuclear plant as described in the following.
Limitorque, as a part of their data input, provided.the overall operator unit gear ratio for the operator shipped.
The equation for calculating the overall gear ratio is:
Revolutions per Minute x Stroke Time x Overall Ratio e No. of Thread Starts Stroke Length x 60 Seconds x Threads per Inch Rancho Seco Nuclear Engineering procedure "IEB 85-03 Loads for Motor-Operated Gate and Globe Valves" states that if the calculated value for the overall gear ratio.in within + or - 20 percent of the manufac-turar's value, it can be assumed that the gearing of the operator is i
"as-cupplied" by the manufacturer.
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The calculated and actual overall gear ration of the valves in the test sample are shown on Table 2.4-1.
In each case, the difference between calculated and actual overall gear ratio is within the + or - 20 percent band width and the assumption that the gearing of all of the operators in the valve test sample is "as-supplied" is accepted.
2.5 SWITCH SETTING PROCEDURES Valve motor operators are controlled by rotary electric switches of two types, limit and torque. Generally, for gate and globe valves, a limit switch is wired to stop the motor after valve opening, a torque switch is w! red to stop valve travel when closing the valve, and a torque switch bypass switch is included in the circuitry to prevent premature torque switch actuation on valve opening. For butterfly valves, limit switches are used to. terminate disc movement in both opening and closing directions.
Each of the switches in the operator controls a valve function.
This section of the report describes procedures followed in setting and adjusting each of the switches to assure proper functioning of the valve. Also included in this section is a description of the procedure for determining size of limiter plate openings and motor overload switch
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settings.
I 2.5.1 LIMIT SWITCH SETTING PROCEDURE The limit switch in the valve opening control circuit is typically set to deactivate the motor operator at some point before full opening such that the disc does not contact the backscat.
Additionally, limit switch contacts are typically used to provide indication of valve position at j
remote locations.
I At Trojan the proper operation of MOV limit switches is routinely checked at the prescribed maintenance interval as a part of the maintenance procedure.
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The criterion for limit switch adjustment is that "The open limit switch should be set to allow full stroke of the valve but prevent the valve from driving or coasting into its backseat."
j To accomplish this goal, the limit switch setting check procedure requires that after opening the valve electrically and observing proper limit switch trip, the valve is put into manual mode and backseated using the handwheel.
If it does not require at least two turns of the hand-wheel to fully backseat the valve, a limit switch adjustment is made.
2.5.2 TORQUE SWITCH SETTING PROCEDURE l
The torque switch must be set in such a manner as to produce, at torque switch cutoff, a stem thrust that assures operation of the valve. An adequate stem thrust is not single valued. Rather, any thrust value within a defined range can assure satisfactory valve operation.
The range of acceptable stem thrust can run from the thrust recommended l
by the manufacturer to actuate the valve at design basis differential pressure, to the thrust that could cause damage to the valve, operator, or motor.
At Trojan, to provide margin in calculated values, the minimum value for the standard range of acceptable thrust has been established at 20 per-cent above the manufacturer supplied thrust required to operate the valve at design basis differential pressure, and the maximum value is taken as 90 percent of allowable thrust.
l The allowable thrust value is the lesser of:
(1) Valve part damage limit set by the valve manufacturer.
(2) Operator maximum thrust set by Limitorque.
(3) Torque limit to prevent stall when operating at minimum voltage.
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On occasion, this standard range cannot be used and must be modified.
For example, if adding the standard margin to required thrust produces a value in excess of the allowable thrust, the range must be adjusted to fit within valve / operator and required thrust limits.
'The original plan for torque switch setting was to record as-found valve conditions with the MOVATS signature, reset the as-found setting to the
-setting recommended by the motor vendor operator to achieve satisfactory operation at the present design basis differential pressure, and rerun the MOVATS test to confirm that the as-left torque switch setting met stem thrust requirements.
At the start of MOVATS testing at Trojan, the plan to use the vendor's recommended settings was changed.
If the as-found settings produced a thrust within the range of acceptability described earlier, no change was made in the as-found torque switch settings.
If the measured as-found thrust was not within the range, the torque switch setting was adjusted to bring it within the range of acceptabil-ity. The MOVATS test of the as-left stem thrust was utilized to confirm that the amount of change in torque switch setting had produced acceptable results.
2.5.3 TORQUE SWITCH BYPASS SWITCH SETTING PROCEDURE The proper operation of the torque switch bypass switch is routinely checked at the prescribed maintenance interval as a part of the maintenance procedures.
The criteria for (bypass) limit switch adjustment for valves that are torque seated (ie, gate and globe valves) is as follows:
"The open bypass limit switch nust operate within a band width of 10% of full stroke. This band width is measured from the point where motor current returns to a normal running level af ter the i
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current peak to pull the gate out of the seat."
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f Verification that the bypass is dropping out some time during the first i
10 percent of valve stroke after completion of hammer blow unseating was made by examining the current trace made as a part of a maintenance procedure.
2.5.4 SWITCH SETTING PROCEDURE FOR QUARTER TURN VALVES operator motor cutoff, in both opening and closing, for quarter turn valves, such as butterfly valves, is provided by limit switches. The
' torque switch serves as backup, and provides protection from valve or operator damage. Torque requirements are determined by disc / seal interaction, not by flow or' differential pressure.
2.5.5 LIMITER PLATE If the maximum thrust that the valve, operator, or motor can tolerate without damage can be' exceeded by the stem thrust developed at the maximum torque switch setting (TSS), a limit must be placed on the torque switch setting to protect the equipment.
1 The device used to provide this limit is called a " limiter plate".
In vendor literature it is also called a " maximum stop setting plate".
This thin plate, with a kidney shaped opening, is placed behind the torque switch name/ calibration plate. The size of the opening limits the setting of the switch to a range from its minimum to a safe maximum.
The MOVATS spring-pack characterization method, described in Section 2.1.1, provides the information to determine the maximum limiter plate setting needed for equipment protection. The slope of the curve defines the change in pounds of stem thrust per unit change in torque switch setting.
The formula for the maximum setting built into the limiter plate is:
Max setting = 1.0 + Allowable Thrust-Thrust at a TSS of 1.0 Delta Thrust per unit TSS change I
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See Table 3.1-1 for maximum settings in the limiter plates.
2.5.6 MOTOR OVERLOAD SWITCH SETTING PROCEDURE PGE has developed and formalized motor overload design criteria.
Valve
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- operation overload protection will be verified against this design criteria..and deficiencies will be corrected and documented.
- Estimated completion date, including field verification, is July 30, 1988, i
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l TABLE 2.4-1 CALCULATED VERSUS ACTUAL OVERALL GEAR RATIO l
Calculated Actual Calculated Overall overall Percent of Valve ID Gear Ratio Gear Ratio Actual MO 8806 37.59 39.11
-3.89 MO 8923A 47.45 46.30 1.39 MO 8923B 47.45 46.80 1.39 MO 8821A 44.06 41.00 7.46 MO 8821B 43.63 41.00 6.41 MO 8835 44.15 41.33 6.82
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MO 112D 40.14 39.11 2.63 l
MO 112E 36.60 39.11
-6.42 MO 8106 51.38 52.20
-1.57 MO 8105 51.38 52.20
-1.57 MO 8803A 41.89 41.33 1.35 l
MO 8803B 43.45 41.33
'5.13 MO 8801A 45.52 41.33 10.14 MO 8801B 45.52 41.33 10.14 l
MO 112B 42.80 43.60
-1.83 MO 112C 47.02 43.60 7.84 MO 8111 93.31 82.00 13.79 MO 8110 64.98 77.00
-15.61 MO 8814 90.04 77.00 16.94 MO 8813 91.17 77.00 18.40 HO 3045A 35.97 36.20
-0.64 MO 3045B 39.91 36.20 10.25 CV 3004A1 135.32 136.00
-0.50 CV 3004A2 128.00 136.00
-5.88 CV 3004B1 135.32 136.00
-0.50 CV 3004B2 135.32 136.00
-0.50 CV 3004C1 135.32 136.00
-0.50 CV 3004C2 135.32 136.00
-0.50 CV 3004D1 135.32 136.00
-0.50 CV 3004D2 135.32 136.00
-0.50 MO 3170 34.50 34.96
-1.32 MO 2947A 32.15 33.11
-2.90 MO 2947B 33.06 33.11
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3.0 TEST PROGRAM RESULTS AND ANALYSIS This section of the report provides the test program results, analysis of the results, and findings made. The section is divided into the follow-ing subjects:
(1) Valve data summary.
(2) Review of problems encountered.
(3) Report of' findings.
3.1 VALVE DATA
SUMMARY
Table 3.1-1 provides a comprehensive data summary for each of the tested valves.
The valve information and data are arranged in the table as follows:
(1) Pages 1 through 3 of the table provide manufacturer information for both the valves and operators, design function, design basis differential pressure (dP), and the as-found and as-left switch settings.
(2) Pages 4 and 5 of the table provide the method of testing, and valve thrust conditions and requirements.
(3) Only two of the 35 valves tested were determined to be inoperable. These were MO 8835 and MO ll2E, which provide cold leg safety injection isolation and charging pump suction of the RWST, respectively. In either case, the valves were backed up by redundant, operable, safety-related valves.
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3.2 REVIEW OF VALVE PROBLEMS ENCOUNTERED This section of the report includes a summary of the problems encountered with valves in the test sample, followed by a detailed discussion and analysis of each problem.
3.2.1
SUMMARY
OF PROBLEMS Table 3.21-1 summarizes motor-operated valve problems found by inspection and testing, by cause. Table 3.21-2 cross references each of the prob-lems with the affected valves.
There tables are located at the end of Section 3.0.
3.2.2 MECHANICAL PROBLEMS 3.2.2.1 Spring-Pack Degradation and Gap l
In the operation of a valve actuator, the energy transferred by the worm, I
which causes the worm gear to rotate, also causes the worm itself to translate axially along the spline of its shaft.
This axial motion is constrained by the counteractive force generated by the compression of the spring-pack such that the distance travelled by the worm is propor-tional to the torque being delivered to the worm gear.
i The spring-pack consists of sets of washers.
When assembled in the motor operator, no gap should exist between the spring-pack and the shoulder
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that holds it in place. Such a gap would permit unconstrained axial movement of the worm corresponding to the gap width.
The most serious problem encountered with spring packs is a change in characteristics which can lead to premature torque switch actuation or, alternatively, overthrusting and valve or operator damage.
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.The principal causes'of the change in characteristics are:
l (1) -Spring-pack degradation.
(2). Excessive spring-pack gap.
Examples of spring-pack degradation are washer flattening which can cause j
premature actuation, grease hardening in the spring-pack cavity, and aging which appears to increase the torque (and thrust) necessary to activate the torque switch.
There are two principal ways for spring-pack gap to occur:
(1) I,oosening of the preload nut.
(2) Flattening of the washers in the spring-pack.
There is no uniformly accepted definition of excessive spring-pack gap.
For this report, spring-pack gap is considered excessive if:
(1) The gap was found and corrected during routine maintenance of the MOV prior to MOVATS testing.
(2) The gap shown on the MOVATS thrust signature exceeds C.020 inches.
The presence of a gap can be observed on the MOVATS thrust signature as an extension of the zero load condition. A gap greater than 0.020 inches has been designated as excessive, based on engineering judgement and is consistent with the definition of excessiveness adopted by Toledo Edison in their response to IE Bulletin 85-03 for the Davis-Besse Nuclear Fower Station.
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The spring packs in two of the valve operators in the test sample of 35, MO 3045A and MO 8835,'were found to be defective.
In the as-found condi-
' tion, MO 8835 torqued out in mid-stroke and the torque switch on MO 3045A
.did not function,~' allowing the motor to stall.
The washers in both MO 8835 and M03045A appeared to be flattened. In each case, the spring-pack was replaced.
The spring-pack gap'in six valve operat' ors was found to be excessive. Of the six, the gap in three (MO 8923A, MO 3170 and M0112E) was found during maintenance or MOVATS testing to be excessive. While for the other three (MO 8803A, MO 112C and MO 2947A) the spring-pack gap was determined to be in excess of 0.020 inches by MOVATS thrust signature analysis.
3.2.2.2 Limit Switch Degradation The limit switch problems most often encountered were chipped or cracked-terminal blocks and cracks in the rotors.
The limit switch terminal block on one valve, MO 8803A, in.this test program, was found to be cracked and was replaced. A limit switch rotor in MO 8105 was-found cracked and was replaced.
3.2.2.3 Torque Switch Degradation Two mechanical problems were encountered with the torque switches in the valve sample:
(1) Breakage.
(2) Imbalance.
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Four torque switches in the test program were replaced during the out-age.
Two, in valve operators MO 8806 and MO 3060B, were replaced because of cracked frames. The other two, in MO 8110 and MO 8821A, were replaced because they could not be balanced satisfactorily.
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Torque switch imbalance is discussed in Section 3.2.4.3.
3.2.2.4 Valve Backseating The stem in valves that are limit opened and are incorrectly adjusted may contact the backseat either before or after the motor has been deener-gized. The effect of frequent backseating during valve operation can be mechanical damage to the disc or stem, which could lead, over time, to failure of the valve to operate.
Three valves, MD 2947B, MO 3170 and MO 8105, of the 35 in the testing program were found to be backseating on opening. Normally, backseating shows on the MOVATS thrust signature as increase in thrust when the backseat is contacted, and for valves MO 2947B and MO 8105, this is how the problem was identified.
For MO 2947B, the size of the thrust increase on backseating, 1,747 lbs, af ter a torque switch cutoff thrust of 21,420 lbs suggests that this is an inertial coastdown type of backseating.
In the case of MO 3170, the increase in thrust observed on the signature was very slight, and not initially recognized as a backseating condition when the signature was analyzed. The most probable cause of the event is i
inertial coastdown after limit switch cutoff. No damage to the valve was observed.
In each case of backseating the problem was minor. No damage was observed and there is no basis for concern that backscating constitutes a threat to operability at Trojan.
Backseating is typically caused by an improperly set limit switch and these three cases are also reported as limit switch problems.
3-5 4
_=
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3.2.2.5 High Running Load Running load is the thrust required to overcome packing and gear friction
.in advancing or retracting the valve stem.
In vandor literature it is called the stuffing box load.
Typically, in thrust requirement calculations, a packing friction load of 1000 lb per. inch of stem diameter is assumed as the average.
High running load is usually caused by excessive packing tightness, although other conditions may also cause high running load. High running load is objectionable because it can, under certain unusual circum-stances, lead to spurious torque switch actuation, resulting in failure of the valve to open or close properly.
High running load is considered a greater problem in smaller valves where stem thrust to overcome packing friction is a greater portion of the total required thrust. The vendor recommends that the combination of stuffing box load and stem load be kept below 33 percent of the seating load.
A running load of 20 percent of the seating thrust has been selected, based on engineering judgement, as a " threshold of concern" and worthy of further investigation.
Five valves in the test sample fell in this category, MO 8806, MO 8923A, MO 8803B, MO 112D, and MO 3045B. An engi-neering review of the valves has been completed and no further action is required to address the high running load.
3.2.2.6 Stem Uncoupling The AFW discharge control valves, CV 3004A1 through D2, are 3-inch balanced control valves.
These valves are normally open and close upon receiving a high-flow signal from a flow element in each line.
A significant feature of these valves is that the motor operator shaft is connected to the valve stem by a coupling. The manufacturer of these 3-6
valves issued a bulletin on December 17., 1986 warning of the possibility of the actuator power stem disconnecting itself from the valve stem if excessive torque was applied in the open direction.
Three of the valves suffered incipit decoupling during MOVATS testing.
The valves were CV 3004A1, CV 3004C2, and CV 3004D2.
These valves are normally stopped in the open direction by the limit switch. The open torque switch serves as protection to prevent damage to the valve or operator should the limit switch fail or the valve jam for some reason.
I For the uncoupling problem to occur, two factors must be present:
l (1) The valve must be restrained in the open direction.
(2) The open torque switch must be set above the threshold for uncoupling.
The required thrust to open this valve is very low because it is a I
cage-type balanced throttle valve. The thrust reported by the manu-facturer as necessary to operate at design basis differential pressure is less than 1000 lbs.
The as-found torque switch settings produced a torque at torque switch cutoff two to three times that necessary to actuate the valve. The three valves that experienced unscrewing of the shaft from the coupling were being tested at torques that exceeded the uncoupling threshold.
The corrective action taken was to set the torque switches on all eight feedwater control valves to a minimum position below the uncoupling threshold value. As-left MOVATS testing, where no uncoupling occurred, demonstrated that the corrective action was successful.
I 3-7 I
3.2.3~' ELECTRICAL PROBLEMS j
3.2.3.1 Operator Wired Incorrectly 1
Two of the 35 valve operators, MO 3045A & B, were found not to be wired I
in accordance with the approved wiring diagram.
.i
~
In each case, it was found that a limit switch was wired in series with J
the torque switch in the valve closing controlfeircuit and the valves were' closing on limit and not torque.
M0.3045A&B are gate valves and should be wired to close on torque as shown.on their~ schematic drawing.
A review of the maintenance history flies showed that there was nothing done that might be related to rewiring the operators after original Plant construction.
Both valve operators were rewired in accordance'with their schematic' l
drawing and returned to service.
In a parallel effort, the wiring of 122 operators was checked during the
~
outage as a part of an electrical equipment qualification review program, and MO 3045A&B were the only two found to be wired differently from that shown on wiring. diagrams.
It is, therefore, concluded that the. root cause of this discrepancy was.
j isolated personnel error during the original Plant construction, and no revision of current Plant practices is considered necessary.
I 3.2.3.2 High Motor Current
-}
Measurement of average running current from the MOVATS motor current signatures indicates that the motor in operator MO 112B is running about 6 percent above its rated amperage in the open direction and 3 percent above in the close direction.
l 3-8 j
l l
l I
1.
i
Measurement of average running current from the MOVATS motor current signatures indicates that the motor.in operator MO 112C is running about 1 percent above its rated amperage in the open direction.
As a matter of good practice, running current should not exceed rated current.
FC.ever, there is no generally accepted standard for establish-ing a threshold of concern on running current for intermittently operated
]
electric motor operators. PGE considers 110 percent of rated current as the threshold for further evaluation.
Neither of the running current conditions described above is considered o threat to valve operability and no investigative or remedial action is planned.
3.2.4 INADEQUATE SWITCH SETTING 3.2.4.1 Torque Switch Bypass Switch It is standard' practice for motor operator circuitry to incorporate a bypass of the torque switch during the initial portion of the opening cycle. The logic for bypassing is that a much larger torque is often required early in the stroke in order for the disc to clear its seat.
The torque switch bypass switch is a limit switch which can be adjusted to remain closed long enough to provide the necessary bypass function on valve opening.
An improperly set bypass switch, which terminates the bypass function too early in the stroke, can lead to failure of the valve to open under some (usually high differential pressure) operating conditions.
l At Trojan, the proper operation of the torque switch bypass switch is I
i routinely checked at the prescribed maintenance interval as a part of the maintenance procedure.
See Section 2.5.3 for a description of this procedure.
3-9 i
e i
During the Trojan 1987 refueling outage, 35 valves were tested.
Of this I
l group, one valve (MO 3170) failed to unseat due to'an improperly set j
torque switch bypass switch. The switch was reset and the valve cycled to confirm that the as-left setting was proper.
The number of valves found to be inoperable due to an improper torque switch bypass switch setting at Trojan (one) is considerably lower:than that found at other plants and published in the record of MOV deficiencies.
The low incidence of this problem at Trojan is due to the method of setting the bypass switch. At Trojan, the bypass switch is set to operate within 10 percent of total stroke band after the motor current returns to a normal running level following hammer blow and unseating.
With current measurement equipment available at Trojan, technicians are able to determine when unseating has been completed and set the bypass switch cutout at a point later in the cycle.
The results indicate that no changes in torque switch bypass switch setting procedure appear to be needed.
3.2.4.2 Limit Switch Setting prob 1 ems An as-found limit switch setting that stops stem travel before near full open position, or allows backseating to occur, is considered a problem.
Based on this criteria, three of the valves in the test sample fall in the problem category.
Each of the three valves, MO 2947B, MO 3170 and MO 8105, were found to be backseating. The specifics of this situation, and corrective action taken, is described in Section 3.2.2.5.
3-10 I
l t
____ A
r-
.L 3.2.4.3 Torque Switch Setting
)
1 I
- For this report,Jan'as-found torque switch setting which produces a stem thrust, opening or closing (or both) outside thefrange of acceptable thrust values is considered a problem situation. The range of acceptability is defined in Section 2.5.2.
A torque switch setting problem is encountered when one of the torque switch settings, independent of its partner, produces an unacceptable thrus t.
Based on this criterion, nine'of the 35 valves in the test sample fall in this problem category. These valves are identified in Table 3.21-2.
Torque switch unbalance is defined as a condition where, with equal torque switch settings, open and close torque switch cutoff thrust is not equal. Some unbalance appears inherent in the operation and MOVATS testing of motor operators. Thrust measurement error can account for a several hundred pound reported difference in opening' and closing thrusts with-the same torque switch settings.
Additionally, torque switch settings reported to be equal may not be exactly equal.
PGE considers torque switch unbalance a problem only when one of the thrust values, either opening or closing, is less than the thrust required to operate the valve at design basis differential pressure, or greater than the upper limit on thrust set by the threshold of valve or operator damage, while the other value is within the acceptable range.
The occurrences of problem torque switch unbalance are reported in Table 3.21-2.
In extreme cases, when both values are outside the range of acceptance in opposite directions, an E appears in Table 3.21-2 rather than the usual X.
3.3 REPORT OF FINDINGS This section is a general record of significant tests, observations, repairs, and service performed on each of the valves in the test sample.
3-11
l i
Installation and replacement of limitse plates, as stated in the follow-
-ing valve descriptions, will be performed during the 1988 refueling outage.
MO 8806 Common SI Pump Suction Valve Type:
8 inch 150 lb Gate Operator Type:
SMBO-15 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke af ter unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a large amount.
Open torque switch cutoff was high enough to operate the valve at the design basis differential pressure of 33 psid.
Closing torque switch cutoff occurred above the thrust level expected to be achievable during minimum voltage operation.
The torque switch was operable even though a crack was observed in the torque switch frame. The switch was replaced.
j l
The torque switch was balanced and the setting on the open side increased to provide additional thrust at torque switch cutoff.
1 Analysis of the as-found signature indicated a spring-pack gap of 0.013 inches.
An adjustment was made to reduce the gap to 0.004 inches.
The as-lef t running load was approximately 20 percent of seating thrust, i
The allowable thrust is limited by the calculated limit on torque to prevent motor stall wher, operating at minimum voltage. The limiter plate opening will be reduced from 2.0/2.0 to 1.25/1.25 to protect the motor from possible damage in minimum voltage operation.
l 3-12
'MO 8923A HSI_ Pump Suction Train A Valve Type:
6 inch 150 lb Gate Operator Type: SMB00-10 The close-to-open' torque switch bypass switch was found to be operating properly, with dropout occurring'within 10 percent of total stroke after unseating. The' switch setting was not changed.-
The torque switch was found to be out of balance by a factor of-1.17'to 1 but produced open and close thrusts substantially above that required to properly seat the disc at the design basis differential pressure.
Spring-pack' gap was found during routine maintenance prior to MOVATS testing. The spring-pack retainer and collar were adjusted to eliminate the. gap. The spring-pack gap observed on the MOVATS signature (0.002 inches) after adjustment'is insignificant.
The as-left running loads, open and close, averaged 22.8 percent of seating thrust.
The maximum allowable' thrust is the calculated thrust produced at rated
- motor torque when operating at minimum voltage. The open torque switch setting was marginally reduced to provide a greater measure of protection-for the motor operating at minimum voltage conditions.
l The limiter plate found has a maximum opening of 3.0/2.5.
This plate i
1 will be replaced with one with maximum openings of 2.0/2.0.
j l
I i
L L
3-13
4 MO 8923B SI Pump Suction, Train B
- Valve Type:
6 inch 150 lb Gate Operator Type:
SMB00-10 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 1.11 to 1 but produced open and close thrusts comfortably above that required to properly seat the. disc.
The allowable thrust is limited by the calculated thrust produced at rated motor torque when operating at minimum voltage. The as-found torque switch setting produced a thrust well below the allowable thrust and the torque switch settings were left as found.
Given the margins involved, no effort was made to achieve better balance.
The spring-pack gap found was approximately 0.013 inches.
Since there is
~
no evidence to indicate that a gap of this size is degrading performance, no effort was made to reduce the gap.
During spring-pack characterization, a torque switch setting of 3.0 produced full spring-pack compression and motor stall.
The limiter plate found has a maximum opening of 2.75/2.75.
This plate will be replaced with a plate with maximum openings of 2.0/2.0 for minimum voltage motor protection and to avoid motor stall.
1 l
1 i
1 3-14
I MO 8821A SI Pump Discharge, Train A i
Valve Type:
4 inch 900 lb Gate 1
Operator Type:
SMB00-25
{
The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating.
The switch setting was not changed.
It was found that the torque switch failed to operate in the open direc-tion and the operator motor went to a stall condition.
Operation in the close direction was normal for the spring-pack model and torque switch setting.
i The torque switch was replaced with a switch having a balance adjustment.
As-lef t thrusts were balanced and in the mid-range between that required to operate the valve at design basis differential pressure and the thrust limit set to preclude damage to the valve.
i No limiter plate was tound. A plate limiting the torque switch setting to a maximum of 1.75/1.75 will be installed.
l MO 8821B SI Pump Discharge, Train B f
Valve Type:
4 inch 900 lb Gate
{
Operator Type:
SMB00-25 The close-to-open torque switch bypass switch was found to be operating i
properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 1.28 to 1 j
and was reset to a balanced condition.
I i
The allowable thrust on this valve is limited by valve parts damage l
f potential. The as-found thrust at torque switch cutoff on closing was i
4 f
3-15 4
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.y higher'than'the valve allowable.- The torque switch settings were adjusted to balance the switch and provide thrusts about 20 percent greater-than that. required to properly operate the valve at design basis differential pressure.
The limiter plate opening was found to be 3.0/3.0 and is to be' replaced Lwith a plate with the openings restricted to 2.0/2.0.
i l
MO 8835 S1 Pump Discharge to Cold Leg 11
\\
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5 Valve Type:
4 inch 1500 lb Gate Operator Type: SMBO-40 The close-to-open torque switch bypass switch was found to.be operating i.
l-properly, with dropout occurring.within 10 percent of totsl stroke after unseating. The switch setting was not changed.
l I
I'
.During routine maintenance prior to MOVATS testing, it was observed that the operator torqued out in mid-stroke.
It was found that this was E
caused by spring-pack malfunction. The washers appeared flattened and j
l did not' provide a. calibrated torque / thrust response. The spring pack was l
l
. replaced.
The allowable thrust on this unit.is limited by the valve. Thrusts found at replacement torque switch cutoff _ demonstrated the switch was in l
balance. Measured thrust values, with the replacement spring pack and as-found torque switch settings, were only marginally lower than valve-5 allowables. Torque switch settings were lowered to provide some 1
additional protection for the valve.
The limiter plate opening will be reduced from 4.0/4.0 to 1.5/1.5.
3-16 i
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'l yy MO 112D CCp Suction from RWST 9
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Valve Type:
8 inch 150 lb Cate
/ Operator' Type: SMBO-15 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating.
)
l il The torque switch was found to be out pf balance by a f actor oi' 1.77 to 1.
t(
s The allowable thrust is limited to the calculated limit on torque to prevent motor stall when operating at minimum voltage. The as-found "f
torque switch cutoff occurred above the thrust level expected to be r
achievable durittg minimum voltage operation. However, it was not above a
valve or operator allowables.
3,t.
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The torque switch sei?.Angs'werd sdjusted to achieve betthe balance and
' reduce thrust at s9 ch cutoff to a level lower than calculated motor b
ti j
stall at minimum vdtago thrust, v
b Theas/leftrunningloads,openandclose, averaged 41percentofseating thrunt.
3s 3
,c The limiter plate openings weroN!ound to be 2.0/2.0.
A new plate with g
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maximum openings of 1.0/1.0 will be installerf' 1
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'A I(,
MO 112E CCP Suction from RWST Valve Type:
8 inch 150 lb Cate t
Operator Type:
SHBO-15 0
3 i
,i The torque switch cut off shotMy af t er the c1me '.o-open torque switch bypass switch dropped out.
Torque switch performar.ca in the h
k open-to-close direction was normal.
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3-17 i
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Investigation revealed. that thu spring-pack preload t..
was' loose q
allowing excessive spring-pack gap Xabout 0.125 inches), and explaining why the torque switch had tripped in Inid-stroke. The preload nut was o:d
,a ff.
tightened to reduce the spring,-pack gap to 0.002 inches, and the operator
[
' performed satisfactorily during'as-left testing.
1-
};
Af ter spring-pack adjustment, the as-found torque switch settings t.-6 4#
provided acceptable and balanced thrusts and were left as-found.
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,)i.
Following spring-pack adjustment, the close-to-open torque switch bypass g
I.
switch was found to be operating properly, with dropout occurring within S #
10 percent of total stroke after unseating.
The allowable thrust is limited to the calculated limit on torque to prevent motor stall when operating at minimum voltage.
Limiter plate openings were found to be 2.0/2.0.
The existing plate will be replaced with one with maximum openings of 1.0/1.0.
HO 8106 CCP Normal Charging to RCS Valve Type:
3 inch 1500 lb Gate Operator Type:
SMB00-25 The close-to-open to que switch bypass switch was found to be operating prolerly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
t As-found thrusts at torque switch cutoff showed the switch to be unbalanced by a factor of 1.32 to 1, and were below the thrust calcal.a*ed by the manufacturer to be necessary i operate the valve at I
desige basis differential pressure, opening and closing.
I During spr:ng-pack characterization a torque switch setting of 2.75 produced full spring-9ack compression and motor stall.
3-18
Torque switch settings were increasod to provide a balanced as-left thrust slightly above mid-range between the thrust calculated to be require 3 to operate the valve at design basis differential pressure and the' threshold of possible damage to the operator.
A limiter plate with an opening to accommodate a maximum switch setting of 4.0/4.0 was found. This plate will be replaced with a plate with maximum openings 2.25/2.25 to protect the salve operator.
MO 8105 CCP Normal Charging to RCS Valve Type:
3 inch 1500 lb Cato Operator Type:
SMB00-25 The close-to-open torque switch bypass switch wes found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
During as-found testing, the MOVATS opening thrust signature showed the valve was backseating.
A limit switch rotor was found cracked and was replaced. The limit switch was adjusted and the as-left MOVATS signature showed that the backseating problem had been corrected.
The spring-pack cavity was found to contain grease and oil. The cavity was cleaned and the spring-pack examined.
Spring pack condition was satisfactory, The torque switch was found to be out of balance by a factor of 1.80 to 1 and was reset to a balanced condition. The switch settings were increased somewhat to achieve this balance and the as-left thrust values are comfortably in the range between the thrust required to operate the valve at design basis differential pressure and'the threshold of possible damcge to the operator, which is the limiting component of the essembly.
During spring-pack characterization, a torque switch setting of 2.75 produced full spring-pack compression and motor stall.
j e
l 3-19
\\
4 The limiter plate found had a maximum opening of 2.75 open and 3.0 close. The plate found is to be replaced with one with maximum openings l
of 2.0/2.0.
MO 8803A CCP Discharge Through BIT Valve Type:
4 inch 1500 lb Cate Operator Type:
SMBO-40 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 1.36 to 1.
The as-found thrust developed at torque switch cutoff, When opening, was less than that considered necessary to properly operate the valve at design basis differential pressure, and as-found thrust developed at torque switch cutoff when closing was greater than the valve allowable set by the manufacturer.
The torque switch settings were adjusted to correct the reported conditions. The as-left thrust values show the switch to be balanced and within the narrow band between the thrust needed to operate the valve at design basis differential pressure and the threshold of possible valve damage due to overthrust.
MOVATS signature analysis revealed a spring-pack gap of 0.042 inches.
The spring-pack was removed, examined, and replaced.
The preload nut was tightened to reduce the spring-pack gap, Which measured 0.003 inches on retest.
As-left values reported are those from the retest.
The limiter plate opening will be reduced from 4.0/4.0 to 2.0/2.0.
3-20 l
A-MO 8803B CCP Discharge Through BIT Valve Type:
- 4 inch 1500 lb Gate Operator Type:' SBMO-40 The.close-to-open torque switch bypass switch was found to be' operating properly,lwith dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
'The torque switch was'found to be out of balance by a factor of.1.22 to 1.
p
- The as-found thrust developed at-torque switch cutoff when opening was l
lslightly less than that considered necessary to operate the valve at design basis differential pressure, and tho thrust developed' at torque switch-cutoff when closing was greater than the valve allowable. set by-
.the valve manufacturer.
The torque switch settings were adjusted slightly to correct the reported conditions. 'The as-left thrust values show the switch to be properly balanced and within a range bounded by the thrust needed to operate the valve at design basis differential pressure and the threshold of possible-valve damage due to overthrust.
Thrust signatures indicate a gap within the spring-pack cavity or assembly of about 0.014 inches. Since there was no evidence to indicate 1
-degraded performance, no effort was made to reduce the gap.
i The:as-left running load was 25 percent of seating load'in the open j
direction and 22 percent of seating load, closing.
The limiter' plate opening will be reduced from 4.0/4.0 to 2.0/2.0.
l
'l l
3-21 l
I
_=__----__ _
1 MO 8801A CCP Discharge Through BIT valve Type:
4 inch 1500 lb Gate Operator Type:
SMBO-40 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring withiis 10 percent of total stroke after unseating. The switch setting was not changed.
The as-found thrust at torque switch cutoff in both opening and closing demonstrated the torque switch was in balance but the thrust was about 6 to 9 percent higher than the valve manufacturer's recommended maximum load on the valvo disc.
The torque switch settings were adjusted to a thrust level which eliminates potential damage to the valve but is above the thrust necessary to operate satisfactorily at design basis differential pressure.
l Thrust signatures indicate a gap within the spring-pack cavity or assembly of about 0.016 inches.
Since there was no evidence to indicate degraded performance, no effort was made to reduce the gap.
A limiter plate with a maximum opening of 2.0/2.0 is to be installed.
MO 8801B CCP Discharge Through BIT Valve Type:
4 inch 1500 lb Gate i
Operator Type: SMB0-40 i
The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The as-found thrust developed at torque switch cutoff when opening was less than that considered necessary to properly operate the valve at design basis differential pressure and as-found thrust developed at 3-22 1
-_-_______--___-_._-_a
torque switch cutoff when closing was greater than the valve allowable set by the manufacturer.
The torque switch settings were adjusted slightly to correct the reported conditions. The as-left thrust values show the switch to be properly balanced and within a range bounded by the thrust needed to operate the valve at. design basis differential pressure and the threshold of possible valve damage due to overthrust.
The spring-pack gap found was approximately 0.009 inches.
Since there was no evidence to'suggest degraded performance, no effort was made to reduce the gap.
The limiter plate opening will' be reduced from 4.0/4.0 to 2.0/2.0 MO 112B CCp Suction from VCT Valve Type:
4 inch 150 lb Gate Operator Type: SMB00-10 1
The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The as-found stem thrust at torque switch trip was within the bounds of thrust required for design basis differential pressure and the valve / operator allowables. However, the closing thrust found was in excess of the limit set to protect the motor from stalling at minimum voltage.
The torque switch was found to be out of balance by a factor of 1.42 to 1.
The situation was improved, with acceptable balance achieved.
The MOVATS trace found a spring-pack gap of 0.010 inches.
The gap was j-reduced to 0.003 inches by adjusting the spring cartridge cap shoulder.
3-23
_-_a_____-___.
II p
1
' Measurement of average running ^ current from motor current signatures j
indicates that the motor was running about'6 percent above its rated amperage in the open direction and 3 percent above in the close direction.
I During MOVATS spring-pack characterization, motor stall occurred at a torque switch setting of 2.50 in the close direction.
- Allowable thrust is limited by the calculated ' limit on torque to prevent motor stall when operating at minimum voltage. The limiter plate opening is to be reduced from 3.0/3.0 to 1.5/1.5 to protect the motor from possible damage when operated at minimum voltage.
MO 112C' CCP Suction from VCT Valve Type:
4 inch 150 lb Gate Operator Type:
SMB00-10 The close-to-open torque switch bypass switch was found to be operating properly,'with dropout occurring within 10 percent of total stroke after
~
unseating. The switch setting was not changed.
The as-found stem thrust at torque switch trip was within the bounds of thrust required for design basis differential pressure and the valve / operator allowables; however, the closing thrust found was in excess of the limit set to protect the motor from stalling at minimum voltage.
The torque switch was found te be out of balance by a factor of 1.43 to 1.
Adjustment was mado during MOVATS testing and the as-left open and close thrust values were within 9 percent.
The thrust signature indicated a gap within the spring-pack cavity of approximately 0.023 inches. The as-left signature demonstrated that the gap does not degrado performance.
3-24
Measurement of average running current from motor current signatures indicate that the motor is running about 1 percent above its rated amperage in-the open direction.
- Allowable thrust is limited by the calculated limit on torque to prevent motor stall when operating at minimum voltage. The limiter plate opening will be reduced from 3.0/3.0 to 2.0/2.0 to protect the motor from possible damage when operated at minimum voltage.
MO 8111 CCp Minimum Recirculation Valve Type:
2 inch 1500 lb Globe Operator Type:
SMB00-15 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The open and close torque switch cutoff thrusts were unequal, as were the
- torque switch settings. Therefore, it is not possible to report the degree of unbalance.
The as-found stem thrust at torque switch cutoff in the open direction was less than that required for satisfactory operation at design basis differential pressure. The torque switch setting in the open direction was increased from 1.0 to 2.25 to allow the operator to deliver the thrust required for valve operation at design basis differential pressure.
A spring-pack gap was measured but found to be insignificant.
Maximum thrust is limited by possible damage to the operator. The limiter plate found had openings of 4.0/4.0.
It is to be replaced with a plate with maximum openings of 2.5/2.5 to protect the valve operator from damaging overthrust.
3-25 l
i
1 MO 8110 CCP Minimum Recirculation Valve Type:
2 inch 1500 lb Globe
]
Operator Type:
SMB00-15 The close-to-open torque switch bypass switch was found to be operating properly,'with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
l The allowable thrust on this valve has been set to preclude damage to the operator. It was found that in the open direction the actual thrust was slightly above the manufacturer's recommended limit.
The torque switch was found to be unbalanced during MOVATS testing and was replaced with a balancable type switch.
As-lef t thrusts were balanced and in mid-range between that required to operate the valve at design basis differential pressure and that allowed by the operator manufacturer.
During spring-pack characterization a torque switch setting of approximately 2.9 produced full spring-pack compression and motor stall.
The limiter plate maximum opening was found to be 4.0/4.0, which will be reduced to 2.5/2.5 to protect the valve operator.
MO 8814 SI Pump Minimum Recirculation Valve Type:
2 inch 1500 lb Globe Operator Type:
SMB00-15 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
3-26 l
As-found thrusts at torque switch cutoff showed the switch to be unbalanced by a factor of 1.44 to 1.
As-found opening thrust was less than the minimum of the range of acceptable values, but greater than the thrust required to operate the valve at design basis differential pressure. The open torque switch setting was marginally increased to I
achieve a better balance between open and close thrusts.
j During spring-pack characterization, a torque switch setting of 3.0 produced full spring-pack compression and motor stall. The lower limiter
)
plates settings will preclude recurrence.
The allowable thrust on this valve is limited by operator damage potential. The limiter plate opening was reduced from 4.5/4.5 to 2.0/2.0 to provide the operator additional protection from possible damage from stem overthrust.
i MO 8813 SI Pump Minimum Recirculation Valve Type:
2 inch 1500 lb Globe Operator Type:
SMB00-15 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
l The torque switch was found to be out of balance by a factor of 1.18 to 1, but in the functional range above the thrust necessary to operate the valve at design basis differential pressure and well below allowable thrust level set to protect the operator. Torque switch settings were
]
not changed.
During MOVATS testing, a spring-pack gap of 0.013 inches was observed.
This condition was corrected by adjusting the spring-pack cap thrust collar one-half turn.
Since the gap found was less than 0.020 inches, it f
is not reported as a problem.
3-27 l
-_-_-_-____-_O
During spring-pack characterization, a torque switch setting of 3.0 produced full spring-pack compression and motor stall.
The operator did not have a limiter plate. One will be installed with maximum openings of 2.5/2.5 to protect the motor and prevent motor stall.
MO 3060B Service Water to Pump Driver Cooler Valve Type:
6 inch 150 lb Butterfly Operator Type:
SMB000-5 During MOVATS testing, it was noted that, at a torque switch setting of 1.5, the operator went into a locked rotor condition. Further investigation revealed that the torque switch was broken. The torque switch was replaced.
Thrust signatures indicate a spring-pack gap of 0.003 inches.
MO 3045A Service Water to the AFW Pump Suction Valve Type:
6 inch 150 lb cate Operator Type: SMB00-10 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
l A limit switch was found in series with the torque switch in the valve l
closing control circuit and the valve was closing on limit and not torque. The MOVATS test was conducted with the limit switch jumpered out of the circuit. The operator was later rewired to eliminate the limit switch from the valve closing control circuit.
When the limit switch was removed from the circuit, the torque switch failed to trio when closing and the motor stalled.
Further inspection 3-28
rl determined that the torque switch did not operate correctly because of a
-defective spring pack.
The spring pack was replaced. The as-found thrusts, with the new spring-pack, were above the minimum voltage limit on thrust, but below valve / operator allowables. The torque switch settings were reduced.
As-lef t thrust was unbalanced and the close thrust is slightly higher than the value calculated as the limit needed to protect the motor from stall at minimum voltage.
Signature analysis indicates an as-left spring-pack gap of approximately 0.018 inches.
No limiter plate was found installed. A plate with maximum openings of 1.25/1.25 is to be installed.
MO 304SB Service Water to AFW Pump Suction Valve Type:
6 inch 150 lb Cate Operator Type:
SMB00-10 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
A limit switch was found in series with the torque switch in the valve closing control circuit and the valve was closing on limit and not torque. The MOVATS test was conducted with the limit switch jumpered out of the circuit. The operator was later rewired to eliminate the limit switch from the valve closing control circuit.
Measured stem thrust at torque switch cutoff was found to bu unbalanced by a factor of 1.34 to 1, but well above that needed to operate at design basis differential pressure.
3-29 4
l' Torque switch settings were reduced to bring the thrust available at cutoff more in line with that required for operation at design basis differential pressure. Shortly before the end of the MOV Outage j
Maintenanec/ Testing program, a decision was made to increase the torque switch settings one-half unit above the MOVATO test level to provide additional operational capability.
The as-lef t thrust reported in Table 3.1-1 is an estimate. No retcat was l
performed because the MOVATS equipment had left the site before the decision to increase the torque switch settings was made.
Signature analysis indicates a spring-pack gap of 0.002 inches.
A so of this amount is insignificant.
The as-left running load was approximately 26 percent of seating load in j
opening and about 34 percent of seating load, closing.
l The allowable thrust is limited by the calculated motor stall torque at minimum voltage. The limiter plate found has maximum openings of 3.0/3.0.
A replacement plate with maximum openings of 2.0/2.0 is to be installed.
CV 3004A1 AFW Discharge Control Valve Type:
3 inch 900 lb Balanced Control Valve Operator Type:
SMCOOO-2 The close-to-open torque switch bypass switch was found to operate properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
This type of valve has a coupling joining the valve stem and the operator shaft. When the valve was operated open into the load cell during the initial MOVATS test, the operator shaft developed sufficient torque to rotate within the coupling. This malfunction also required limit switches to be reset.
3-30
O After this situation had been corrected, the MOVATS test was repeated with minimum torque switch settings. The minimum setting successfully 1
cutoff motor action before coupling rotation on opening.
4
.i As-lef t thrusts were balanced and both as-found and as-lef t thrusts were sufficient to operato the valve at design basis differential pressure.
i The spring-pack gap of 0.002 inches observed on the thrust signature is insignificant.
No' limiter plate was found. A plate with a maximum opening of 1.0/1.0, to preclude coupling rotation, is to be installed.
CV 3004A2 AFW Discharge Control Valve Type:
3 inch 900 lb Balanced Control Valve Operator Type:
SMB000-2 The close-to-open torque switch bypass switch was found to operate i
properly, with dropout occurring within 10 percent of total. stroke after unscating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 1.28 to 1, with the closing thrust 100 lb higher than the upper limit on the range of acceptability, but lower than valve allowable.
Thrust signatures indicate a spring-pack gap of approximately 0.010 inches. Since the size of the gap falls be19w the limit defining excess, and the operator achieved target thrusts at as-left torque switch cut off, the gap was not changed.
The torque switch was balanced and torque switch settings were left as found. The open switch setting wna later reduced to 1.0 to protect against possible coupling rotation similar to that which occurred in other valves in this group.
I l
l 1
l 3-31
)
i
a
'The limiter plate found allowed maximum settings of 3.0/4.0.
It will be replaced with a plate with maximum openings of 2.0/2.0.
L i
I CV 3004B1 AFW Discharge Control l
l
' Valve Type:
3 inch 900 lb Balanced control Valve Operator Type:
SMB000-2
[l The close-to-open torque switch bypass switch'was found to operate properly,'with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The' torque switch was found to be out of balance by a factor of 1 56 to 1, but as-found opening and closing thrusts were.both within the range of acceptability.
An insignificant 1y small (0.001 inch) spring-pack gap was observed on the MOVATS signature.
The thrust levels found, in both opening and closing, were functional.
l The thrust was adequate to operate the valve at design basis differential pressure and insufficient to cause damage to the valve.
The torque switch was brought into better balance and torque switch settings were left as-found. The open switch setting was later reduced to'1.0 to protect against possible coupling rotation similar to that j
which occurred in other valves in this group.
The limiter plate found had maximum openings of 3.0/3.0.
It will be replaced with a plate allowing maximum settings of 2.0/2.0, j
3-32
CV 3004B2 AFW Discharge Control Valve Type:
3 inch 900 lb Balanced Control Valve Operator Type:
SMB000-2 The close-to-open torque switch bypass switch was found to operate properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
l The torque switch was found to be out of balance by a factor of 1.68 to 1; however,. the thrust levels found, in both opening and closing, were functional. The thrust was adequate to operate the valve at design basis differentia 1' pressure and insufficient to cause damage to the valve.
During spring-pack characterization, a torque switch setting of 3.0 caused full spring-pack compression and motor stall.
Thrust signatures indicate a spring-pack gap of approximately 0.001 inch, Which is insignificant.
Torque switch settings were left as-found and not balanced. The open switch setting was later reduced to 1.0 to protect against possible coupling rotation similar to that which occurred in other valves in this group.
The limiter plate found had maximum openings of 3.0/3.0.
It is to be replaced with a plate with maximum openings of 2.0/2.0.
CV 3004C1 AFW Discharge Control
-Valve Type:
3 inch 900 lb Balanced Control Valve 1
Operator Type:
SMB000-2 j
The close-to-open torque switch bypass switch was found to operate z
properly, with dropout occurring within 10 percent of total stroke after 3
\\
5 unseating. The switch setting was not changed.
3-33
The torque switch was found to be out of balance by a factor of 1.36 to 1.
However, the thrust levels found, in both opening and closing, were within the range of acceptability. The thrust was adequate to
)
operate the valve at design basis differential pressure and insufficient to cause damage to the valve.
\\
The torque switch was balanced and torque switch settings were left as l
found. The open switch setting was later reduced to 1.0 to protect f
I against possible coupling rotation similar to that which occurred in
]
other valves in this group.
A spring-pack gap of 0.002 inches observed on the thrust signature is insignificant.
During spring-pack characterization a torque switch setting of 3.25
]
produced full spring-pack compression and motor stall.
The limiter plate found allowed maximum settings of 3.25/3.25.
It will i
be replaced with a plate with maximum openings of 2.0/2.0.
CV 3004C2 AFW Discharge Control Valve Type:
3 inch 900 lb Balanced Control Valve Operator Type: SMB000-2 The close-to-open torque switch bypass switch was found to operate properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
j i
The torque switch was found to be out of balance by a factor of 1.41 to
)
1.
However, the thrust levels found, in both opening and closing, were
]
within the range of acceptability. The thrust was adequate to operate I
the valve at design basis differential pressure and insufficient to cause l
1 damage to the valve. The torque switch was balanced and torque switch l
settings were left as found.
3-34 i
l 4
._ _ ]
This type of valve has a coupling joining the valve stem and the operator shaft. When the valve was operated open into the load cell during the initial MOVATS test, the operator shaft developed sufficient torque to j
rotate.within the coupling. This malfunction also required limit switches to be reset.
l After coupling inspection, the MOVATS test was repeated with minimum 1
torque switch settings. The minimum setting successfully cut off motor action before coupling rotation on opening.
As-lef t thrusts were not balanced and are sufficient to operate the valve at design basis differential pressure.
A spring-pack gap of 0.001 inch, observed on the thrust signatures, is insignificant.
The limiter plate found allowed maximum se.ttings of 3.5/3.5.
It is to be replaced with a plate with maximum openings of 1.0/1.0, to preclude coupling rotation.
CV 3004D1 AFW Discharge Control Valve Type:
3 inch 900 lb Balanced Control Valve Operator Type:
SMB000-2 The close-to-open torque switch bypass switch was found to operate properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 1.17 to 1.
However, the thrust levels found, in both opening and closing, were within the range of-acceptability. The thrust was adequate to operate the valve at design basis differential pressure and insufficient to cause damage to the valve.
3-35 I
i
Thrust signatures indicate a spring-pack gap of about 0.003 inches, which is insignificant.
Torque switch settings were left as found. The open switch setting was later reduced to 1.0 to protect against possible coupling rotation similar to that which occurred in other valves in this group.
The limiter plate found allowed maximum settings of 3.5/3.5 it will be replaced with a plate with maximum openings of 2.0/2.0.
CV 3004D2 AFW Discharge Control Valve Type:
3 inch 900 lb Balanced control valve Operator Type:
SMB000-2 The close-to-open torque switch bypass switch was found to operate properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 1.54 to 1.
However, the thrust levels found, in both opening and closing, were within the range of acceptability. The thrust was adequate to operate the valve at design basis differential pressure and insufficient to cause damage to the valve.
L This type of valve has a coupling joining the valve stem and the operator shaft. When the valve was operated open into the load cell during the initial MOVATS test, the operator shaft developed sufficient torque to rotate within the coupling. This malfunction also required limit switches to be reset.
After coupling inspection, the MOVATS test was repeated with minimum torque switch settings. The mininum setting successfully cut of f motor action before coupling rotation on opening.
3-36
As-lef t thrusts were not balanced but are sufficient to operate the valve at design basis differential pressure.
1
)
Thrust signatures indicate a spring-pack gap 0.009 inches, below the level considered to be a problem.
l The limiter plate found allowed maximum settings of 3.5/3.5.
It is to be replaced with a plate with maximum openings of 1.0/1.0 to preclude coupling rotation.
PO 3071 AFW Turbine Driver Trip and Throttle Valve Valve Type:
4 inch 600 lb Gate Operator Type:
SMB000-2 The close-to-open torque switch bypass switch was found to be operating properly. with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
l '
The torque switch was found to be out of balance by a factor of 1.71 to 1, and the closing thrust at torque switch cut off was larger than the upper limit of acceptable thrust, but not high enough to allow motor stall at minimum voltage.
The closing torque switch setting was reduced and left at a torque switch cutof f thrust below the calculated stalled motor thrust at minimum l
- voltage, l
i MOVATS thrust signatures indicate a spring-pack gap of about 0.006 inches.
l No limiter plate was found. A limiter plate with maximum openings of 3.0/3.0 will be installed.
3-37 l
MO 3170 AFW Turbine Driver Steam Inlet Valve Valve Type:
4 inch 600 lb Globe Operator Type:
SMBO-40 In the as-found condition the close-to-open torque switch bypass switch tripped before disc unscating. The switch was adjusted to open within the range specified.
At the initiation of MOVATS testing, it was observed that the spring-pack was loose. The spring pack was removed, disassembled, inspected for damage (washer flattening), and returned to service.
preload was set at 4640 lbs.
As-left spring-pack gap was measured as 0.003 inches on the thrust signatures.
Af ter spring-pack rework, stem thrust at torque switch cutoff, opening and closing, was found to be balanced but insufficient to insure satisfactory operation of the valve at design basis differential pressure. Torque switch settings were increased and as-left testing demonstrated sufficient thrust at torque switch trip to operate at design basis differential pressure.
The valve was observed to be backseating on opening.
The condition was investigated.
No damage to the valve was found and the open limit switch was adjusted to preclude future occurrence.
Maximum stem thrust is limited by the operator. A limiter plate with maximum openings of 3.0/3.0 is to be installed to prevent inadvertent operation at a thrust level higher than the operator limit.
3-38
MO 2947A Motor Driven AFW pump Discharge Control valve Type:
6 inch 900 lb cate Operator Type:
SMBO-40 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unseating. The switch setting was not changed.
The torque switch was found to be out of balance by a factor of 2.21 to 1.
In the open direction, thrust marginally exceeded the operator allowabic.
In the close direction, thrust was insufficient to ensure operation at design basis differential pressure.
Investigation of this condition revealed that the torque switch to spring-pack connection was misaligned by one gear tooth.
The switch was reset to a balanced condi&.lon and icft about midway in the l
range between the thrust required to operate at design basis differential i
and operator allowable. The as-found torque switch settings are not considered a problem since these settings would have cut off stem thrust in the range of acceptability if the torque switch had been properly aligned.
As-found thrust signatures revealed a 0.068 inches spring-pack gap.
An adjustment to the thrust collar was made reducing the gap to 0.012 inches.
The limiter plate, which had been removed, is to be replaced with a plate with a maximum opening of 2.5/2.5 to protect the valve operator.
l MO 2947B Motor-Driven AFW pump Discharge Control Valve Type:
6 inch 900 lb Gate Operator Type:
SMBO-40 The close-to-open torque switch bypass switch was found to be operating properly, with dropout occurring within 10 percent of total stroke after unscating.
The switch setting was not changed.
3-39
The torque switch was found to be unbalanced by a factor of 1.33 to 1 and in the open direction thrust was insufficient to insure valve operation at design basis differential pressure. The switch was reset to a balanced condition and left about midway in the range between the thrust required to operate at design basis differential and operator allowabic.
Thrust signatures indicate an apparent spring-pack gap of 0.006 inches.
The opening thrust signatur.3 showed that the valve stem was contacting the backseat with a thrust of approximately 1747 lbs.
The limit switch was not adjusted, e
The limiter plate found had a maximum opening of 2.0/2.0, which was the as found torque switch setting.
.It was necessary to remove this plate to increase the thrust at torque switch cutoff to the point where operation at design basis differential pressure can be assured.
A new limiter plate will be installed with maximun openings of 2.5/2.5 which is sufficient to protect the operator, the limiting component, from damage.
l 3-40
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l TABLE 3.21-1
SUMMARY
OF MOTOR VALVE PROBLEMS BY CAUSE j
l j
Number of Percent of Valves Total Type of Problem Affected (35 Valves) i Mechanical f
Spring Pack. Degradation 2
6 Excessive Spring Pack Gap 6
17 Limit Switch Degradation 2
6 Torque Switch Degradation 4
11 Torque Switch Imbalance 4
11 valve Backseating 3
9' High Running Load 5
14 Electrical Operator Wired Incorrectly 2
6 High Motor Current 0
0 j
Inadequate Switch Settings Torque Switch Bypass Switch 1
3
-Limit Switch 3
9 Torque Switch 9
26 I
h
_ _ _ _ _ _ _ _ _ _ _ ___ _= _ _.. _ _ _ _. _... _.. _ _.
c* -
Page'1 of 3 TABLE 3.21
SUMMARY
OF MOTOR VALVE PROBLEMS BY VALVE AND CAUSE Spring.
' Spring Limit Torque Pack Pack Gap Switch Switch Torque Repair Adjust Repair Repair Switch Valve ID' Required Required-Required Required Unbalance MO 8806.
I MO 8923A X
MO 8923B MO 8821A X'
MO 8821B MO 8835-I MO 112D MO 112E X
MO 8106 MO 8105 X
'X MO 8803A X
X E
MO 8803B X
MO 8801A MO 8801B MO 112B MO-112C X
-MO 8111 MO 8110' X
i MO'8814 MO 8813 MO 3060B I
MO 3045A X
MO 304SB CV 3004A1
.CV 3004A2 CV 3004B1 CV 3004B2 CV 3004C1 CV 3004C2 CV 3004D1 CV 3004D2 ho 3071' MO 3170 X
MO 2947A X
X MO 2947B Total Occurrence 2
6 2
4 4-1
I-Q, 1
Page 2 of 3 i
TABLE 3.21-2
SUMMARY
OF MOTOR VALVE PROBLEMS BY VALVE AND CAUSE-High Valve ID Backseat Run Load MO 8806 X
MO 8923A X
MO 8923B MO 8821A MO 8821B MO 8835-MO 112D X
MO 112E MO 8106 MO 8105 X
MO 8803A MO 8803B X
MO 8801A MO 8801B MO 112B
- MO 112C MO 8111 MO 8110 MO 8814 MO 8813 MO'3060B MO 3045A MO 3045B X
CV 3004A1 CV 3004A2 CV 3004B1 CV 3004B2 CV 3004C1-CV 3004C2 CV 3004D1 CV 3004D2 MO 3071 MO 3170 X
MO 2947A MO 2947B X
Total Occurrence 3
5 i
i
________.m___
L-W.
Page 3 of 3-TABLE 3.21-2
SUMMARY
OF MOTOR VALVE PROBLEMS BY VALVE AND CAUSE Torque Operator High Torque Switch Limit-Wired Motor Switch Bypass Switch-Valve ID Incorrectly Current Settings Switch
. Settings MO 8806 MO 8923A~
MO 8923B MO 8821A
'I MO 8821B X
MO 8835 MO 112D MO 112E MO 8106 X
MO 8105 X
MO 8803A MO 8803B MO 8801A.
X
.MO 8801B X
MO 112B
.NO 112C MO 8111' X
MO 8110 MO 8814
~MO 8813 MO 3060B MO 3045A X
X MO 3045B X
CV 3004A1 CV 3004A2 CV 3004B1 CV 3004B2 CV 3004C1-
'CV 3004C2 CV 300AD1 CV 3004D2 MO 3071 HO 3170 X
X X
MO 2947A
'MO 2947B X
X Total I
' Occurrence 2
0 9
1 3
i
_ _ _ _ _ _ _ _ _ '_i______._____z____
]
l l
4.0 CONCLUSION
S 4.1 SWITCH SETTINGS Torque Switch Bypass Switch This test program has demonstrated that the Trojan method of setting the motor operator torque switch bypass switch is satisfactory and requires no changes.
The success of this method can be attributed to the development, at Trojan, of a motor current measurement device, similar to the MOVATS motor current signature, which identifies when hammer blow occurs and allows setting of the torque switch bypass switch cutoff later in the cycle.
Limit Switches In-review of the data, it can be concluded that Trojan has few limit switch setting problems, and no reason to consider any major program changes.
Torque Switches The torque switch (re) setting program described in this report provides assurance that cach of the valves in the test se.mple will operate satis-factorily at design basis differential pressure. A detailed investiga-tion of methods manufacturers use in determining required thrust for operation at design basis differential pressure, coupled with spring pack characterization and demonstration of operational capability at maximum differential pressure, show that as-left torque switch settings for test sample valves are correct.
4-1
'o o.
' Butterfly Valve Switches There was one butterfly' valve'in the test sample, MO 3060B. TestingL demonstrated that the as-found limit switch and torque switch settings.
were adequate'.to assure valve operability at. design basis differential
_ pressure.
No' changes in quarter-turn valve switch setting practice is required' or recommended.
4.2 CURRENT PROGRAMS As a. result of the Motor-operated Valve Analysis and. Testing System-(MOVATS) program, limiter plates will be installed on the valves as described in Section 3.3 of this report. In addition, the motor-operated valves in the scope of.the' Bulletin will be reviewed against new motor overload design criteria developed by PGE.
Deficiencies will.be cor-rected and documented with an estimated completion date of July 30, 1988.
PGE will continue to monitor valve switch settings under the current testing, unintenance, and inspection programs for the Trojan Nuclear Plant.
. lant' procedures provide for servicing of safety-related valves p
on a 3-year cycle. This servicing includes inspection for parts degrada-tion, replacement of' worn or damaged parts, and routine tests to check the validity of switch and breaker settings that includes monitoring the motor operator characteristics. Traces are made of motor operator.
current, torque switch, bypass switch, and limit switch actuation points as the valve is cycled open and closed.
The In-Service Testing Program for Trojan stroke tests the safety-related valves to ensure proper opera-tion. These procedures and programs will ensure that the proper switch settings are maintained and the valves are able to perform their J
safety-related function in the event of a design basis accident.
L 4-2 4
1
^-
t.
APPENDIX A THRUST REQUIREMENT CALCULATIONS In closing a torque seated valve, sufficient stem thrust must be developed before torque switch cutoff to close the valve against the design basis differential pressure and seat the disk to produce a leak tight seal. Typically, the torque switch is set to trip at a thrust value above the calculated seating load at the design basis differential pressure.
In opening a valve, it is desirable that the torque switch be set at a point where the unscating hammer blow torque developed does not trip the switch. However, since the torque required to unseat the disc is unpredictable, a torque switch bypass switch is included in the opening control circuit so that the torque switch is not operational u-til after hammer blow.
Calculation of the proper thrust is usually based on experience and/or empirical formulas. The most generally recognized method of calculating required thrust is the one developed and published by Limitorque which is quoted here from Limitorque's " Gate and Globe Valve (Operator) Selection procedure", dated May 21, 1979.
"All standard gate and globe valves require a predictable torque / thrust to seat or unseat against a given differential pressure. This seating torque / thrust is generally expressed in terms:
" THRUST = differential pressure x seat (port) area x valve factor + stuffing box load + stem load
"(where) stuffing box load is explained below and stem lond = stem area x line pressure
'*r0RQUE = THRUST x stem factor i
A-1
-4
" Stuffing Box Load -1000# for stem diameter up to 1" 1500# for stem diameter up to 1 1/2" j
2500# for stem diameter up to 2 1/2" 4000# for stem' diameter up to 4" 5000# for stem diameter above 4" "The stem load (piston effect) is the force required to drive the valve stem into the valve.
Although this force is always present in gate valves, it is not always present in a globe valve in terms of (stem area x line pressure).
A more appropriate equation for a globe valve is (stem area x line pressure - stem area x differential pressure) as the latter is included in the basic seat area equation.
l "For simplicity and additional safety factor, the stem load... Will be used for all gate and globe valves (for both opening and closing the valve, even though, theoretically, it is a closing load only)."
The three loads do not act simultaneously, but since the nature of load interaction is not fully understood and cannot be clearly defined, simultaneous application of all throo loads is a conservative simplifying assumption.
1 The manufacturer of each valve selected for MOVATS testing was asked to provide:
l
. Valve stem thrust required to actuate the valve at design basis differential pressure, opening and closing.
Maximum stem thrust at which point the weakest valve member will yield, opening and closing.
In addition, the MOVATS signature analysis group provided thrust requirement information from their testing data bank.
(
)
i A-2
o MOVATS and-the manufacturers were also asked to describe the procedure used to calculate required stem thrust.
Information received on procedures and calculated results are described in this section of the report.
Of the 35 valves in the testing program, ;U5 were conventional gate or globe valves, to which the Limitorque thrust requirement calculation procedure, or some' variation thereof, is applicable.
In reviewing the required stem thrust values submitted by the manufacturers, it became clear that there was some non-uniformity of approach. This study was initiated to determine how each of the manufacturers calculated required stem thrust, leading to a standardized method.
-The thrust requirement values submitted by the valve manufacturers and MOVATS are compared with the as-lef t torque switch cutoff thrust, the Limitorque equation, and manufacturers allowabic thrust, for opening and closing, in the Table A-1.
The mathematics of each calculational method are diccussed below:
Limitorque The Limitorque equation for calculating Gate Valve seating thrust at design basis differential pressure described earlier can be stated mathematically as:
Thrast Required, Tr = DP + SBL + SL where DP = Differential Pressure x Port Area x Valve Factor SBL = Stuffing Box Load SL = Stem Load = Stem Area x Line Pressure A-3 c___
For Globe Valves the same formula is applicable, except that:
)
SL = Stem Area x (Line pressure - differential pressure)
l The Anchor-Darling calculation.is similar to the Limitorque approach, except for the handling of stem load.
l For Anchor Darling Gate Valves.
l Valvo closing thrust req'd = Tf + Ts + Tp i
Valve opening thrust req'd = Tf - Ts + Tp
)
where Tf = Port Area x Differential' Pressure x Valve Factor Ts = Stem Load = Stem Area x Line Pressure Tp = Packing Drag For Globe Valves, The same equations are used, but the calculation of stem load becomes:
Ts = Stem Area x (Line pressure - Differential pressure) 3 Where design basis differential pressure is equal to system (line) pressure J
l the term is zero and Stem Load is not a factor, which produces an equal l
. thrust requirement in each direction, j-A-4 l
I t-
Copes-Vulcan The Copos-Vulcan equations for calculating required stem thrust are:
For Gate Valves Closing Tr = DP + PL & SL where Tr = Thrust required DP = Dif pressure X Port Area x Valve Factor PL = Packing load = 4 x stem diameter x sq root of diff pressure (minimum 250 lb)
SL = Stem load = Stem area x Line pressure Opening Tr = DP + PL where Tr = Thrust required DP = Dif pressure x Port Area x Valve Factor PL = 4 x Stem diameter x sq root of diff pres (minimum 250 lb) l 1
Pacific Valve Pacific Valve uses the Limitorque method, except that the stuffing box load i
1 is calculated as 1000 lb x stem diameter in inches, rather than using Limitorque's 1/2 inch increment load table quoted earlier.
This accounts for the several hundred pound difference in thrust required reported by Pacific Valve for MO 3045 A & B, with a 1-1/8" stem diameter, and the Limitorque number shown in Table A-1.
l A-5 l
l-I l
s Velan Valve
.Velan uses the Limitorque formula, with its own packing load experienco.
The closing thrust reported by Velan is that calculated by the Limitorque formula for both gate and globe valves.
I l
For gate velves, Velan adds 10% to the calculated Limitorque figure for opening, as extra margin for unseating hammer blow.
This margin is not added for globe valves.
l l
MOVATS l
-The MOVATS equations for calculating stem thrust required for Gate Valves j
are:
For opening, Tr = 1.3 x DP x (0.3 x PA + 0.225 x PA) where Tr = Thrust required DP = Differential pressure PA = Valve port. area For closing, Tr = 1.3 x DP x (0.3 x PA + SA) where Tr = Thrust required DP = Differential pressure PA = Valve port area SA = Valve stem area I
l l
A-6
'e and for Globe Valves, the equations are:
For Flow Under the Seat:
For opening,. Tr = 1.3 x DP x PA.
Where.
Tr = Thrust required DP = Differential Pressure I
PA = Port Area For closing, Tr = 1.3 x (DP x PA + LP x SA)
Where Tr = Thrust required DP = Differential Pressure PA = Port-Area LP ='Line (or system) Pressure SA'= Stem Area i
i For Globe Valves with Flow Over the Seat:
I For opening. Tr = 1.3 x LP x PA For closing, Tr = 1.3 x DP x PA where Tr = Thrust required LP = Line Pressure DP = Differential Pressure PA = Port Area A-7 l
i
_a
d The values calculated using the equations developed in this Appendix are j
compared with manufacturers, and MOVATS, submittals in Table A-2.
.i 1
i Of the various calculational techniques analyzed, there is no evidence that one is more accurate than another in predicting actual thrust required for satisfactory operation at design basis differential pressure.
1 I
Further, tests at maximum differential pressure do not verify that the thrust developed at torque switch cutoff is what is (the minimum) required for satisfactory operation. Rather, the differential pressure tests only demonstrate that the thrust developed is adequate, without regard to the l
amount of margin above the actual requirement involved.
I I
The original plant design decision to use manufacturer furnished required stem thrust as a basis for setting torque switch cutoff was sound at the 1
time it was made, and has produced satisfactory results.
i l
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p TABLE A-2 THRUST REQUIREMENT CALCULATIONS MOVATS MOVATS, MOVATS MOVATS MFG MFG.
MFG'
. MFG Open-Open Close Close Open Open Close Close Thrust Thrust Thrust Thrust Thrust Thrust Thrust Thrust Valve No.
Cale Rept Cale Rept Calc Rept Calc Rept
' Anchor-Darling.
H02947A
.26,965 26,964 19,507 19,513 10,200 10,220 16,505 16,530 M02947B 26,965 26.,964 19,507 19,513 10,200 10,220 16,505 16,530 M03170 21,574 21,574 24,025 24,026 19,755 19,755 20,290 Copes-Vulcan
- 0112B 700 701 516 517 558 494 647 673.
M0112C 700' 701 516 517 558 494 647 673 M0112D 3,879 3,879 3,234 3,776 M0112D 987 987 684 1,658 M0112E 3,879 3,879 3,234 3,776 M0112E 987 987 684 1,658 M08806 3,879 3,879 3,234 3,726 M08806 987 987 684 715 M08923A 2,458 2,460 2,141 2,393 M08923A 585 585 507 498 M08923B 2,458 2,460 2,141 2,393 M08923B 585 585 507 498 pacific b
M03045A 1,974 1,974 1,257 1,256 2,092 2,073 2,092 2,073 M03045B 1,9],4 1,974 1,257 1,256 2,092 2,073 2,092 2,073 Velan M08105 9,930 9,973 9,161 9,118 9,402 9,293 8,547 8,448 M08106 9,930 9,973 9,161 9,118 9,402 9,293 8,547 8,448 i
M08110-9,635 9,692 13,122 13,180 9,653 9,697 9,653 9,697
]
M08111 9,635 9,692 13,122 13,180 9,653 9,697 9,653 9,697 H08801A 17.019 17,102 14,934 14,984 14,287 13,500 12,988 12,886 M08801B 17,019 17,102 14,934 14,984 14,287 13,500 12,988 12,886 l
M08803A 17,019 17,102 14,934 14,984 14,287 13,500 12,988 12,886 I
M08803B 17,019 17,102 14,934 14,984 14,287 13,500 12,988 12,886 M08813 5,424 5,456 7,387 7,420 6,090 6,114 6,090 6,114 M08814 5,424 5,456 7,387 7,420 6,090 6,114 6,090 6,114 l
M08821A 9,581 9,586 8,407 8,441 8,764 9,102 7,967 8,274 1
M08821B 9,581 9,586 8,407 8,441 8,764 9,102 7,967 8,274 l
M08835 9,581 9,586 8,407 8,441 8,764 8,785 7,967 7,986 j
Calc = calculated Rept = Reported
]
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