ML20217N230
| ML20217N230 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/22/1997 |
| From: | Berry E NORTHEAST NUCLEAR ENERGY CO. |
| To: | |
| Shared Package | |
| ML20217N155 | List: |
| References | |
| 1-OM-7.5, NUDOCS 9708260071 | |
| Download: ML20217N230 (9) | |
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. Page 1 of 9 O Millstone Uu. One OPERATIONS MANUAL SECTION 7.5
" OPERATION OF MOTOR OPERATED AND MANUAL VALVES" Sponsor: E. E. Berry [/2 Z[f 7 Effective Date k TABLE OF CONTENTS PAGE NUMBER 1.0 PURPOSE 2 2,0 APPLICABILITY 2
3.0 REFERENCES
2 4.0 RESPONSIBILITIES 2 5.0 INSTRUCTIONS FOR MOTOR OPERATED VALVES 2 6.0 - . INSTRUCTIONS FOR MANUAL VALVES 6
- 7.0 INSTRUCTIONS FOR PROBLEM GATE VALVES 7 8,0 - ENGINEERED VALVE PACKING 9 Approved by:
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9708260071 970819 gDR ADOCK 05000P S
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.1.0 : PURPOSE 1.1= In the event excessive stem or seat leakage occurs it may become necessary to apply additional closing or opening force in either the seated or backseated position.
Such action may lead to housing degradation, loose or broken mounting bolts, bent valve stems or other failures. Consequently, this instruction shall be consulted whenever operational concerns exist with motor operated or manual valves which could tequire other than normal stroking practices.
2.0 APPLICABILITY 2.1 This instruction applies to the Shift Managers for the course of action to be taken in the event a degraded condition exists for motor or manual operated valves.
3.0 REFERENCES
3.1 SOER 83-9; " Valve Inoperability Caused by Motor-Cperator Failures", dated October 21,1983.
3.2 SOER 84-7; " Pressure Locking and Thermal Binding of Gate Valves", dated December 14,1985.
3.3 SOER 85-2;" Valve Mispositioning Events involving Human Error" dated February 28,1985. ,
3.4 "ACR 1946, "Limitorque 10CFR21 Notification, SMB-00s" 3.5 - "ACR 1947, " Failure of SMB-2 to operate due to missing spacer in worm shaft assembly" 4.0. RESPONSIBILITIES 4.1 Operators must be familiar with the requirements contained in this instruction prior to
. operating valves which are governed herein.
5.0 INSTRUCTIONS FOR MOTOR OPERATED VALVES CAUTION r
Failure to comply with this guidance may result in -actuator and/or valve damage (Vs) - due to thermal expansion and/or contraction during p' lant operating Mode changes.
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O 5.1 Backseating of Motor Operated ValvesJdQV.)
Certain valve designs may incorporate a stem backseat which is designed to minimize valve stem leakage when the valve is in the open position and backseated.
Limit switches are normally used to ensure the MOV does not backseat when opened electrically. If the MOV does not have a safety related opening or closing function, the circuit design may employ use of the torque switch to purposely
. backseat the valve.
In the event high leakage exists, it may be necessary to consider additional backseating force. This practice will usually decrease stem leakage but also increases the potential for damage to valve components. The combined effect of these mechanical and thermal stresses may result in the failure of motor housings, valve stems, stem nut and other related components. Consequently, in order to optimize plant performance and ensure continued safe operation motor operated backseating efforts will be analyzed on a case by case basis.
MOVs cannot be considered operable if they have been placed in manual, without .
Engineering Review, per the steps outlined in Step 5.1.1. An electrical stroke must O follow and the MOV stroke time verified as acceptable. The following considerations must be addressed prior to backseating MOV's:
. If placed on the backseat, the closing stroke time could be higher than TS/1RM requirements.
. Backseat only valves with packing leaks that cannot be corrected by normal packing adjustment.
- Do not use valve backseating as el alternative to timely replacement of packing.
- Contact the System Manager to confirm that the valve has a backseat and that backseating is permissible.
. Maintenance should be requested to backseat valves. For unusual circumstances, where prompt Operator actions are required, Operators may manually backseat a valve. /
. Refer to Technical Specifications for any Limiting Condition for Operation and Action Requirements (i.e., PCIV, ECCS)
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['v) 5.1.1 A procedure shall be developed for the degraded valve which will require PORC approval and concurrence from the Maintenance and Operations Department Managers. As a minimum this procedure must address:
. Initial condition of the degraded valve.
. Technical Specification LCO requirements are satisfied prior to disabling any control feature.
. Removal of any fuses in the motor operator controller.
. Use, as appropriate, of clamp on ammeter to monitor starting or locked rotor current.
. Safety precautions (i.e. electrical gloves, tagging, etc.)
. Provision for motor operator and valve cooldown.
. Restoration of affected motor control devices.
. Method used to place the valve on the backseat ( i.e. manually opened or (D
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closed with a torque wrench applied to handwheel, electrical operation with MOV Diagnostic Test equipment, etc.).
. Il manually operated, whether MOV is operable or inoperable.
5.1.2 Ooerations with a Backseated MOV 5.1.2.1 All backseated MOVs shall be identified and carried on the shift turnover sheet until removed from its backseat.
5.1.'2.2 The backseated motor operated valve will be so identified by a yellow caution tag placed on its control switch.
5.1.2.3 If the plant is to be taken to cold shutdown any backseated valve must be removed from its backseat belote cooling down to prevent s undue stress to the valve.
ij 5.1.2.4 To avoid the effects of thermal cyclic stresses on valve parts, backseating should be performed when the valve body is at its normal operating temperature (Hot or cold), so that the force into !
the backseat is at a minimum. l m._.__- _ _ _ _____
1 oM-7.5, Rw O Page 5 of 9 L) 5.1.3 llandwheel Closure of Motor Ooerated Valves ,
A major contributor to valve and valve operator damage is unnecessary, excessive force applied during handwheel closure. Excessive force caused by over-tightening the valve closed, over stressing, and ultimately separation or cracking at the bolted flange between the housing cover and main housing as well as potential damage to the thrust bearing in the housing cover.
Manual closure of such valves when aided by a cheater bar can result in torque values in excess of design.
5.1.4 Recirc pump discharge valve 1-RR-2A(B) controllogic has been modified.
The valve no longer fully backseats resulting in the potential for leakage through the body. If required, the valves can be manually back seated using the handwheel thus reducing leakage. Contact the System Manager if manual backseating is recuired.
5.1.5 MOVs that have been manually seated (closed) shall be declared inoperable with respect to remote opening capabilities. Valve operability shall not be
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b restored until isolation requirements (i.e., stroke time) have been demonstrated.
Refer to Technical Specifications and TRM for any Limiting Condition for Operation and Action Requirements.
5.1.6 The risk of valve / actuator damage is even greater when manually seating a motor operated butterfly valve Personnel cannot rely on handwheel resistance as an indication of valve seating due to the large mechanical advantage provided by the motor operator.
5.1.7 When possible use remote indications to verify valve position (local indications may not be located at the exact open and closed position and may be very inaccurate).
5.2 Electrical ooeration of n/loVs Electrical Design Engineering identified a concern for the number of consecutive motor starts permissible during testing of MOVs. Even though MOV motors are protected with thermal overloads or thermal overload alarms, there does exist the potential to unnecessarily overheat the MOV motor and potentially cause motor damage.
V As a rule of thumb, AC powered MOVs that run for over 1 minute in either direction, can be started 7 consecutive times in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. AC powered MOV's that stroke in less than 1 minute in either direction, can be consecutively started 14 times in one hour. For DC powered MOVs, the starting criteria is
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more restrictive: DC MOVs that run for over 1 minute in either direction, can only be started 3 consecutive times in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. DC MOVs that stroke in less than 1 minute in either direction, can be consecutively started 5 times in one hour. Depending on_the motor size, the required cool down could be as much .
as 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> before the next start.
During normal IST surveillance testing, this is of no concern, as MOV motors are started only twice within a brief period (i.e., open to close, then close to open). However, there are a few safety related MOVs that are jogged open ;
or closed to control flow, such as 1-LPC-4A,1-LPC-4B,1-RR-2A,1-RR-28, 1-SD-4A,1-SD-48,1-LP-44A,1-LP-448. Engineering Studies
- have shown that the number of jogs in one hour (i.e , alternating starts and stops of the i actuator within a 3 second period) can be safely exceeded without overheating the motor. However, logging should be minimized as much as nossible.
- Memo to J. Stanford from J. Chiloyan, DE-CY-96-0164, dated March 15,
.1996.
O QJ 6.0 INSTRUCTIONS FOR MANUAL VALVES 6.1 Backseating of ManualValvas 6.1.1 Backseating a manual valve requires Shift Manager approval and Operations. l Manager notification.
6.1.2 All backseated valves shall be identified and carried on the shift turnover sheet until removed from the backseat.
6.1.3 Backseating of manual valves is to be done using the handwheel only. Do nat use cheater bars to backseat manual valves.
6.1.4 If the plant is to be taken to cold shutdown any backseated valve must be ,
removed form its backseat before cooling down to prevent undue stress to the valve.
6.2 Ooeration of Manual Valves .
6.2.1 All manual valves with handwheel operators are to be seated by handwheel only.
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'V 6.2.2 Manual valves will be checked in the doteil position by going to close until seated.
1 oM 7 5. Rw, O Page 7 of 9 6.2.3 Manual valves will be checked in the Dma position by partially going to close, (VT then opening until backseated, then closing one-quarter turn of the handwheel.
6.2.4 If any question arises on valve position, it should be resolved prior to signing the valve lineup sheet. Do notrely on stem or gear indicators for valve position indication.
6.2.5 Operations personnel are directed to exercise discretion with the use of
< cheater bars on valve operator handwheels. With orior SM anoroval.
Operations personnel may use a cheater bar to seat a manual valve.
6.3 Use of Motor Ooerated Power Tools on Manual Valves 6.3.1 Due to the high torque developed by these power tools when used on manual valves, the following precautions must be followed:
e in both the closed and open directions, the first and last 5% of valve travel mwil be done by hand, a Operators must have firm footing when using power tools on manual i - valves. It is not permissible to use them on ladders of any type (portaole platforms and portable stairs are acceptable).
. Two people must be present to use power tools on manual valves.
7.0 INSTRUCTIONS FOR PROBLEM GATE VALVES 7.1 Discussion of Thermal Binding 7.1.1- Due to design, a wedge gate valve body contracts a proportionally greater amount than the disk when the valve cools. This causes the seat to squeeze the disk tighter so that reopening the valve may not be possible without reheating the body.
7.1.2 Excessive closing force can also contribute to thermal binding. The additional force causes the disk to be driven into the seat more tightly and, on cooling, binding can result. This phenomenon can occur in solid and Flexwedge Gate Valves.
72 Discussion of Hvdraulic Pressure Locking n
V 7.21 When a gate valve of Flexwedge or Parallel Wedge Design is closed, system pressure becomes trapped in the bonnet cavitv. See' and/or packing leakage usually prevents any significant pressure buildup in the bonnet cavity.
Sometimes, however, pressure can buildup and the valve will fail to open.
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'"' 7.2.2 The first potential cause of pressure locking occurs when a differential pressure across the disk exists. The high pressure side of the disk can be forced away from its seat by high pressure fluid allowing it to enter and pressurize the bonnet cavity. If the differential pressure across the disk is subsequently reduced or removed, the high pressure remaining in the bonnet cavity can provide sufficient force on the disk seat to prevent the valve from being reopened.
7.2.3 The second potential cause of pressure locking can occur with the valve closed and the system full of cold water. As the system temperature increases, the liquid trapped in the bonnet cavity rises in temperature and pmssure accordingly. The valve need only be in proximity to a heat source (theoretically a pressure increase of 100 psia would occur form a one degree Fahrenheit rise in temperature inside the bonnet). This situation, along with preventing proper valve operation, could also cause deformation of valve paris and excessive leakage around the valve.
7.3 Discussion _of Differential Pressure Disk Pinchina 7.3.1 Differential Pressure Disk Pinching could affect Solid Wedge Valves. In this l 3 scenario, the valve has been closed with excessive force and low system
'd pressure. If the system pressure were to increase, the valve body expands allowing the disk to travel further into the seat, if the system pressure is subsequently reduced, the velve body would contract, pinclung the disk in the seat.
7.4 Prevention and Potential Soluilons to Gate Valve Problems 7.4.1 Avoid excessive force when manually closing gate valves, especially during cooldown. Along with this, ensure that valve actuators are properly adjusted to prevent excessive force when closing automatically operated gate valves.
7.4.2 Avoid rapid cooldown rates which can cause aMerential temperature conditions to exist between gate valve disks.
7.4.3 During cooldown, slightly open and reclose susceptible valves. This may be required several times during a cooldown to prevent thermal binding or hydraulic pressure lock.
1 7.4.4 The following corrective actions may be considered if a gate valve becomes stuck and written procedures do not exist to provide the necessary technical
, guidance and safety precautions. These actions require Shift Manager and V Engineering approval. s 7.4.4.1 Remove Valve Insulation to allow cooling.
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[d\ .-7.4.4.2 For a pressure locking condition, loosen packing to allow the bonnet cavity to depressurize.
7.4.4.3 Heat the valve body externally to expand the seat and relieve the pressure on the wedge disk. This may also require loosening the packing to prevent bonnet pressurization.
8.0 ENGINEERED VALVE PACKING 6
8.1 Since many MOVs and Manual Gate Valves have modified valve packing configurations, adjusted to specific torque values, request Maintenance to adjust packing glands to the proper torque, f
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