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Chemical&ProcessTechnology:RequirementsofSDVBypassPressurizationLine
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RequirementsofSDVBypassPressurizationLineWednesday,December5,2007
Displayedproblem?ClickHere
Shutdownvalve(SDV)iscommonlyusedinoilandgasfacilitiesforsafeandisolationtoavoidescalationofhazardousmaterialfromonesystemtoanothersystem.Itiscommonlycontrolled
by Emergency ShutdownSystem (ESDS)which is highly reliable system.
Inearlierpost,ihavelisted12mainfeatures
requiredbyaShutdownvalve.Normally theShutdown valve is maintained
in open position using Instrument Air. In the event
ofInstrumentairfailure,theShutdownvalvewillshutclosed.
BypassPressurizationLineDuringstartup, theshutdownvalve
inclosedposition.Theupstreamofshutdownvalvewillbepressurizedathighpressure(i.e100barg)whilsttheshutdownvalvemaystillkeptat23barg.Highdifferentialpressureacrosstheshutdownwillresultshightorqueagainsttheactuator.ItmaynotbeCOST
effectiveandjustifiabletoprovideanlargeactuatorjusttoopentheShutdownvalve.Amorereasonableapproachwillbeprovidingabypasslinewitha
small shutdownvalveanda throttling valveacross themain
shutdownvalve forinitialpressurizationpurpose.Seebelowimage.
BlockValve GateValve ValveGas ValveBall
e.g.ASME,JIS,BS,GB,etc,...HowtoapplyvalveequationinHYSYSDepressuring?Highpressureandmoderate/lowtemperatureoperationarecommoninoilandgasindustry.Highpressuresystemwithlargevesselswillleadtolargeinventoryanditsignificantlyincreaseshazardousleveltopersonnelandassets...
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12/10/2014
Chemical&ProcessTechnology:RequirementsofSDVBypassPressurizationLine
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ShutdownBypassValveduringEmergencyTheremaybeanemergencysituatione.g.plantfire,seriousleakage,etctakeplaceduringpressurization
period and demand downstream system to be isolated immediately
andreliablyforsafetypurpose,thusathebypassvalveshallbeconnectedtotheEmergencyShutdownSystem(ESDS)toenablepropershutdown.
DistancebetweenBypassShutdownValveandThrottlingValveHighpressuredropacrossthethrottlingvalvemaypotentialleadstoverylowtemperaturedownstream
of the throttling valve due to JouleThompson (JT) effect. The
fluidtemperaturedownstreamof throttlingmaydropsbelowsubzero (Less
thanzerodegreeCelsius).Sensibleheatinthepipingwilltransfertocoldfluidandslowlyapproachingthissubzero
temperature.The"coldness"will travelback toupstreamof
throttlingvalveandmayreachestheShutdownvalve.ItpotentiallycausetheupstreamShutdownvalvebodytemperature
drops below subzero aswell.Moisture from atmospherewill freeze at
theShutdown valve body and potentially cause the stem stuck at open
position. This
willposeshazardtothesystemastheshutdownmaynotabletoclosewhenitisdemanded.Itis
recommended to provide to locate throttling valve 600mm downstream
of theShutdownvalve.Similararrangementintheblowdownline.
HeatTracingDownstreamofShutdownvalveJTeffectmayleadstosweating/iceformatexternalpipe.Applicationofanticondensationcoatingandheattracingonthebypasspipewillhelptoavoidsweating/icing.
Depends on fluid composition, low temperaturemay leads to
hydrate formation or
iceformedandpotentiallypartially/totallyblockthesmallpressurizationline.Heattracingmayhelp(maynotavoid)keeptemperatureabovehydrateformationtemperature.
BypassLineSizeBypass linesize isverymuchsubject to
fluidcomposition,downstream INVENTORY ,differential pressure, etc.
The linemaybe sized such that the flowrate
ismaximumbutwithouthydratefromationoriceformedatreasonablepressurizationtime.Insomeevent,noiselevelmaybeanissueandneedsadditionalassessment.
BlockValveGateValveValveGas
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Chemical&ProcessTechnology:RequirementsofSDVBypassPressurizationLine
http://webwormcpt.blogspot.com/2007/12/commonrequirementsofsdvbypass.html
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AutomatedPressurizationAsdownstreampressureslowlyincreases,thedifferentialpressurewilldropsandleadtolowflowpassingthethrottlingvalve.Operatormayneedstoslowlyincreasetheopeningtoincrease
the throttling valve. Some plant imposing minimum manning and
increaseautomation,thosetheopeningofthrottlingvalvemaybeautomatedwithapressurecontrolwith
a bypass control valve.This typeof arrangement shall beproperly
engineeredasthere are many issues such as hydrate, iceform, noise
ASSOCIATE with thisarrangement.
RelatedTopicShouldweinstallButterflyvalveforPressureReliefValve(PSV)isolation?AnotherdescrepancyfoundinAPIStd521Jan200712FeaturesrequiredforShutdownValve(SDV)WhyRestrictionOrificeissomedistancefromBlowdownvalve?RequirementofoverpressureprotectiondevicesonsystemdesigntoPIPINGcode
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