1. Air Products Internal Use Only
RX 7 Modification to Lubrication Pressure Control System
Jordan Watkins & Maintenance Team May 7, 2013
Project Description
Thisdocumentisto informthe teamof a modificationtobe done to the pressure control onthe seal
lubricationsystemforreactor7. The newmodificationwill includeadifferential pressure controllerthatwill be
run inthe DCS. The differential pressure controller(DPIC)willbe linkedtoanew pressure transmitter(PT)
readingthe lubricationpressureandlinkedtoan existingpressure transmitterreadingthe reactorheadspace
pressure.The DPICwill keepaconstant50 psigdifferential pressureatthe seal. The planwouldbe tohave this
modification doneduringthe nextavailabledowntime. We will implementthisonRX7 lubricationsystems
usinga newDPIC,PT and I/Palsokeepone spare on the shelf forbothsystems.The P&IDshowingthe
proposedfix canbe foundat the endof thisreport.
Business Premise
As documentedinapreviouslywrittenseal failure reportwe have seen significantevidenceshowingusthatthe
seal facesare beingover-pressurized.Duringnormal operationof the currentsystemthe lubricationpressure
remainsat a constant1150 psig.On the reactor side where the seal isperformingitsduty,aspentrends show
us that the reactor headspace pressure will fluctuate anywhere from 0psigto 900 psig.As youcan see inthe
bestcase scenariowe have a differential betweenpressuresof 250 psigand forthe worstcase scenariowe
have a differential betweenpressuresof 1150 psig.Accordingto JohnCrane,the manufacture of our current
seal design,the recommended maximumpressure differential is50 psig. These fluctuationsinpressure cause
the sealsmatingringsto deflectcausingwearonthe facesthat theywere notdesignedfor,thereforereducing
the reliabilityof the seal. Onaverage we will have acatastrophicseal failureevery6months.Due tothe size
and complexityof thisseal we have itshippedoffsite tobe repaired increasingthe costtorepair.
Proposed Solution
Due to the highpressure fluctuations seenbythissystemthisprojectproposestoinstall a pressure tracking
digital control valve asprescribedbyJohnCrane Lemco. The digital control valve will maintainaconstantseal
lubricationline pressure of 50psigabove the Reactor 7 headspace pressure. Thiswill entail addinganew
pressure transmittertothe seal lubricationline thatwill readthe pressureinthe lube oil systemconnectedto
the seal.ThisPressure transmitterwill replace the currentpressure indicatingcontrollerPIC-3798.The system
will alsorequire adigital linerunfromthe currentpressure transmitteronRX7 (PT-3700). Bothpressure
transmitterswill sendasignal to the DCS. Thisprojectwill alsorequire anew I/Pconnectedtothe newdigital
pressure control valve. Thee I/Pwill receive the signalfromthe DCSand senda pneumaticsignal tothe control
valve.The newsystemfromJohnCrane Lemcowill include acustommade mountingbracketforthe newdigital
control valve and 2 new pressure transmitters.
2. Air Products Internal Use Only
Design Basis
ProcessRequirements
RX 7 seal lubricationsystemiscurrentlysetupwithaplan54 pipingplanwhichentailsanexternal lubricator
providingTurbofloRO-32oil ata constantpressure of 1150 psig.The pressure iscurrentlysetbyPIC-3798
sensingthe lubricationline andsendingasignal tothe existingP/P(PY-3798).The PY sendsa pneumaticsignal
to PCV 3798 whichsetsthe pressure at1150 psig. The Reactor7 headspace pressure can fluctuate from0 psig
to 900 psigwitha ramp upperiodof 30 minutes. The JohnCrane seal that iscurrentlyinstalledrequiresthatat
a minimumthe lubricationsystemmaintain50 psigabove the processpressure anda flow rate of 1 to 4 gpm.
The systemwill have anywherefrom250 psigand 1150 psigdifferential onthe seal.
The new systeminstalledonthe seal lubricationline will be controlledfromthe DCSmaintainingalubrication
pressure of 50 psigabove the processpressure.A diagramof the new systemisshownbelow thisreport.
The current lubricationsystemdoeshave acritical interlockI-379whichincludespressure switch low (PSL-
3799) whichissetat 1100 psig. If thisswitchessense apressure below the setpressureitwill sendasignal to
close twopneumaticvalves(NV-3799A & NV-3799B).The protectionsystemalso includesanalarmPAHL–
3799 whichwill alarmif the systempressure exceeds1325 psig.In the eventthese valvesclosethe systemhas
an accumulatorwith a pre-charge of 80 % of the normal operatingpressure onthe lubricationsystem.The pre-
charge isutilizedtogive maintenance timetotroubleshootthe issue priortoshuttingdownthe reactor.
The newproposedsystem will require thatthe critical interlockbe changed.The systemwill keepthe high
pressure switchandalarmbut the lowpressure switchlogicwill be changed.The DCScontrollerwill be
connectedtothe interlocktosense if there isa change indifferential pressure somethinginthe order of ± 10%
activate the solenoid closingNV-3799A&B.The DCScontrollerwill be programmedtoincorporate anewsystem
protection. Thisinterlockwill alsoactivate the same solenoidtoopenanew pneumaticvalve onthe discharge
of the lubricationlineaccumulator. The accumulatoronthe lubricationlinewillhave athirdline addedtothe
discharge valve.Thisline will be the outletline forthe storedenergyinthe accumulator.The currentline on
the accumulatorwill include acheckvalve thatisallowingsystempressure tobuildupinsidethe accumulator
but notallowitto discharge.Inthe eventthe DPSL sensesadecrease indifferential pressure the solenoid,NXV-
3799, will close NV-3799A&Band openthe new pneumaticvalve onthe new discharge line off the
accumulator.
Electrical Requirements
The newproposedsystemwill require threelinesruntothe DCS, one will be forPT-3700 RX 7 headspace
pressure transmitter,the secondline will be foranew pressure transmittersensingthe lubricationline anda
thirdline forthe outputsignal fromthe DCS to the new I/P.The New I/Pwill sendapneumaticsignal tothe
newdigital pressure control valve.The DCSwill be configuredtokeepthe new pressuretransmitter50 psig
above whatit isseeingfromPT-3700 (RX7 HeadSpace Pressure Transmitter).
Physical Considerations
The new lubricationpressure control systemwillrequire the removal of the current processof controllingthe
pressure tomake way forthe newsystem.The currentpressure control valve (PCV-3798) will be removedas
well asthe P/P(PY-3798). Alsothe pressure indicatingcontroller(PIC-3798) will be removed.All associated
3. Air Products Internal Use Only
pipingwill be removedaswell.A newdigitalpressurecontrol valve,I/Pelectrical signal topneumaticsignal
converterandpressure transmitterwillbe installedontothe currentlubricationreservoirutilizingacustom
made mountingbracket.New3/8” stainlesssteel tubingwillbe usedtoconnectthe I/Pto the digital pressure
control valve aswell asconnectingthe newpressure transmitteranddigital control valve.New lineswill be run
to the DCS for 3 instruments.The projectwill alsorecommendthatthe pressure switchlow isremovedfrom
the current interlockandadigital line runforthe new logicto control overpressure andunderpressure.
The accumulator onthe seal lubricationline will be modifiedtohandle the variable pressure change.We will
add a check valve onthe inlet tothe accumulator.The modificationwill alsoinclude anew line runfromthe
discharge of the accumulatorthat will connecttothe lubricationline.Thisline will incorporateapneumatic
valve thatis normallyclosedduringoperationandacheckvalve to preventbackpressure.Itwill activateopen
froma signal sentfromthe critical interlockwhichisconfiguredinthe DCS to sense achange in the set
differentialpressure.
PipingConsiderations
All pipingwill be 3/8"316 SS withSwedglockfittings.New tubingwill be requiredforthe new digitalpressure
control valve withI/Ppositionerandnewpressure transmitter.AllassociatedpipingconnectedtoexistingPCV
and PICwill be removed. New 3/8“tubingwill be ranforthe modificationstothe operationof the accumulator
and incorporate a½” carbon steel line forthe new pneumaticvalve.A pressure indicatorline willbe included
on the inletline tothe accumulatoranda temperature indicatoronthe line beforethe new digitalPCV.
Estimated Cost of Project:
Description QTY. Total Price
Digital Pressure Control System 1 $11,950
DCS Configuration and
Installation
1 $7,070.28
New Piping and valves 1 $2,000
Installation of piping and valves 1 $3,000
Total Project Cost - $24,020.28
Steps Involved
1. Pre-Runwire forthree instrumentsthatwill be connectedtothe DCS
2. Remove CurrentPCV-3798and associatedtubing
3. Remove CurrentPY-3798 and tubing
4. Remove PIC-3798 andtubing
5. Remove PSL-3799 and associatedinterlockconnections.
6. Install newdigital pressure control valveusingcustommade bracket
4. Air Products Internal Use Only
7. Install newpressure transmitterwherePIC-3798usedto be
8. Run new3/8" SS tubingto all instruments
9. ConnectDCS wiringtonewPCV,new PTand PT-3700 to DCS
10. Configure DCStocontrol Differentialbetweenseal lubricationpressure andRX7 processpressure
11. Install solenoid/valve onoutletof seal lube oil systemAccumulator
12. Configure Accumulatorsolenoid/valve toopenuponfailure of lubricator
13. Configure Interlock379 to activate uponchange in differential pressure
14. Install checkvalve onthe discharge andinletof lubricationaccumulator
Benefits and Reliability Improvements
The newpressure trackingsystemwill addagreat degree of systemreliabilityforthe seal.Beingable tokeepa
constant50 psig differential onthe seal will eliminate the leadingcause of seal failuresforreactor7 seals.The
currentpressure systemwill allowforexcessive pressure swingonone side of the seal whichdoescause
deformationof the matingrings.Once the matingringsdeformwe getanunevenwearpathon the seal faces
whichwill openupovertime leadingtoa slow lubricationleak.Also amore commonproblemwithinthis
currentsystem,we will see adramaticdecrease inreactorpressure,causingthe highpressure onthe
lubricationline toslamagainstthe seal matingringsandagainsta retainingring. The retainingringisusedto
preventthe matingringfrommovingoutof place duringa pressure fluctuation.There are fourtabsequally
sectionedonthe matingringto keepitinplace.There isa 0.005” clearance betweenthe retainingringtabsand
the matingring governedbyJohnCrane specifications.Once the matingringhasbeenslammedagainstthe
retainingringa fracture will occurand a catastrophicfailure of the seal will follow.
The costs associatedwithone seal failure forreactor7 will have bothmaintenance costsand productioncosts.
The cost affectingmaintenanceare freightcosttoshipthe seal to and fromthe repairfacility,replacement
parts, repairshop labor,internal materials,andmaintenance time toremove andreplace the seal. The total
cost to maintenance averages$50,000 per seal failure.The costtoproductionfor the last seal failure was
$24,894 for10 hours of downtime.Therefore the total costof one seal failure is$74,894. Withthe currentrate
of twoseal failuresayear,the annual cost of the seal failuresis$149,788.
Beingable tosuccessfullymanipulate the lubricationpressure tomaintaina50 psi differential onthe reactor
headspace pressure will ensure thatwe eliminate the mostcommoncause of seal failuresinReactor7and
planto proactivelyreplace sealsbeforetheyfail unexpectedly.
