lucius learning series - mov seismic weak link

LuciusLucius Learning SeriesLearning Seriesuc usuc us ea g Se esea g Se es

Motor Operated ValveMotor Operated Valvei ii i k i k l ik i k l iSeismic Seismic –– Weak Link AnalysisWeak Link Analysis

© 2010, Lucius Pitkin, Inc.

Typical Typical Gate ValveGate Valve

Lucius Learning Series: MOV Seismic Weak Link©2010, Lucius Pitkin, Inc. All Rights Reserved

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Typical Globe ValveTypical Globe ValveTypical Globe ValveTypical Globe Valve


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Typical Butterfly ValveTypical Butterfly ValveTypical Butterfly ValveTypical Butterfly Valve


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General Valve Component General Valve Component

Stems Discs

ppDescription (Description (Gates and Globes)

Outside screw, non-rotating, rising.

Solid wedge. Flexible wedge.

Outside screw, rising-rotating,

Parallel. Globe.

Two piece with coupling,-lower piece rising, non-rotating -upper piece

Disc lifters T headrotating, upper piece,

rising-rotating. T-head. Lifting arm. Threaded into


Threaded into wedge. 55

Categories Categories of Valves (Gates and of Valves (Gates and Globes)Globes) Pressure retaining components

Body.B

Globes)Globes)

Bonnet. Bonnet bolts. Disc (pressure boundary). Pressure seal gasket retaining ring.

Non pressure retaining componentsNon-pressure retaining components Yoke. Operator flange.p g Yoke bolts. Operator bolts. Stem


Stem. Torque arm. 66

Disc Variations (Gates and GlobesDisc Variations (Gates and Globes)


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Gate Gate and Globe Valve Considerationsand Globe Valve Considerations

Gate valves Majority react out the stem torque through the T-Majority react out the stem torque through the T

head into the disc and then through body rails or seats.

Some use torque armSome use torque arm.

Globe valvesGlobe valves Majority react out the stem torque through a torque

arm or stem key into a bushing in the yoke.O i i t ti t t ti On a rising rotating stem, no torque reaction -however, torque losses as the stem rotates at the packing, disc, and the stem nut adapter


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Gate and Globe Valve Considerations Gate and Globe Valve Considerations ( t( t))

The actuator reacts the applied torque/thrust back through the yoke

(cont(cont))

structure.

On closing: Stem is in compression. Disc is in compression. All other components are in tension.p

On opening: Stem is in tension. Disc is in tension. All other components are in

compression.


p

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Gate Valve DP vs. Stroke Position Gate Valve DP vs. Stroke Position


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Gate Gate Valve Typical Closing SequenceValve Typical Closing Sequence


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Gate Valve Typical Opening SequenceGate Valve Typical Opening Sequence

Lucius Learning Series: MOV Seismic Weak Link©2010, Lucius Pitkin, Inc. All Rights Reserved121212

GlobeGlobe Valve Typical Opening SequenceValve Typical Opening SequenceGlobe Globe Valve Typical Opening SequenceValve Typical Opening Sequence


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Pressure Pressure Locking/Thermal Locking/Thermal Binding (PL/TB)Binding (PL/TB)——1Binding (PL/TB)Binding (PL/TB)——1

What is PL/TB? P l ki t d b t fl Pressure locking: pressure trapped between flex wedge and bonnet causes differential pressure exceeding operator thrust capacity.g p p y

Thermal binding: caused by differential expansion between the valve body and disc.

Susceptible valves: Safety related gate valves Safety related gate valves. Valves essential to reliable plant operation in high

energy systems.


gy y

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Disc PinchingDisc Pinching Disc pinching Similar to thermal binding.g In closed valve, pressure increases in valve body,

causing body to expand. When disc seat area expands the stem can move further into theexpands, the stem can move further into the seat. If the pressure should decrease, the body reflexes causing the disc to pinch into the seat.

Susceptible valves: Safety related gate valves with flex or solid

wedge. Valves essential to reliable plant operation in high


Valves essential to reliable plant operation in high energy systems. 1515

Disc Disc Pinching: ProcessPinching: Process

Source: NUREG/CP 0152 Vol 2


Source: NUREG/CP-0152, Vol. 2

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MOVMOV Calculation ConsiderationsCalculation Considerations-- Stroke TimeStroke Time Stroke Time Considerations For rising Stem MOVs:

St k Ti St T l * 60 * OAR Stroke Time = Stem Travel * 60 * OARRPM * Stem Lead

For quarter turn (Butterfly) MOVs

Stroke Time = HBC Ratio * 60 sec/min * OARRPM * 4


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-- Valve Weak Link Valve Weak Link The valve weak link analysis is performed to

determine the maximum load the valve can b bj t d tbe subjected to.

The evaluation reviews each component in The evaluation reviews each component in the valve to determine the maximum load the weakest component can safely sustain.

Loads are calculated for “continuous” loading and “one-time” loadingloading and one-time loading


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Seismic Seismic -- Weak Link ReviewWeak Link ReviewS WL Evaluation ProcessS-WL Evaluation Process


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Weak Link Calculation Method Weak Link Calculation Method

Stressallowable - stressotherallowable other

Thrust = f (geometry)

where

Thrust = maximum thrust for evaluated componentStressallowable = allowable stress for evaluated componentstressother = component stress due to pressure / gravity / seismicf (geometry) = geometric relation between thrust and the component

stress that would be caused solely by thrust: stresscomponent = Thrust x f (geometry)


2020

lucius learning series - mov seismic weak link

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