80 May 2006 www.pump-zone.com PuMPs & systeMs
Q. How can I troubleshoot bolted flange connection leaks?
A.Oneofthebestavailabletoolstoaidindeterminingthecauseofleakageinaboltedjointiscarefulexaminationofboththegasketinusewhentheleakageoccurredandthejointitself.
Ifpossible,notethelocationoftheleakonthegasketandflange.Italsoishelpfultoknowwhethertheboltsarestill
tight or loose.However, this is not alwayspossible todetermine
because bolts may have seized or been
bound.Also,whenremovingbolts,allboltsmaybeaffectedoncethefirstbolthasbeenremoved.
Someofmost common joint leakagemechanisms
aregivenbelow,alongwithsomeremediestopreventrecurrenceoftheleakage.
Chemical AttackGasket is badly corroded
Corrosionofmetalgasketsisprobablymoreeasilydiag-nosedthanthatofrubberorfibergaskets.Damagetonon-metallicgasketscanbemisdiagnosedsincemechanicalandchemicalattackmightlooksimilar.
Non-metallicgaskets canbecrushed,whichwill
typi-callycausesplittingofthegasketinarcsthatareparalleltothecircumferenceofthegasket(asopposedtoradialsplits).Erosionof
thegasketwill causegouging at thegasket
ID,butthedamagewillbelimitedtooneortwoareas.Edgesoferodedareaswillbesmooth,notragged,andthesurfaceattheIDwillbeconcave.
If the damage is due to chemical corrosion, select
areplacementmaterialwithimprovedcorrosionresistance.
Mechanical DamageGasket is extruded excessively
Extrusion typically is seen with soft and
semi-metal-licgasketmaterials.Ifexcessextrusionisobservedwithsoft
gaskets,selectareplacementmaterialwithbettercoldflowpropertiesorbetterloadcarryingcapacity.
For semi-metallic gaskets, excessive extrusion can bereduced by:
minimizing clearance between mating
flangepartssuchastongueandgrooveareas,bridgingtheclearancee.g.,usingguideringswithspiralwoundgaskets,orwithagasketwhoseI.D.isgreaterthantheflangeborediameter.
Gasket is extensively
crushedNon-metallicgasketsthathavebeensubjectedtoextreme
compressiveloadswilltypicallysplittodissipatetheappliedstress,whereasaspiralwoundgasketwillexhibitseverebuck-lingofthewindings.Areplacementshouldbeselectedwithbetterloadcarryingcapacity.
Topreventcrushingofspiralwindings,provideameanstostopovercompressionofthegasketbyusinganinnerringorre-designofthematingflanges.
Troubleshooting Bolted Flange Connection Leaks
Figure 1. Non-metallic gasket showing chemical attack.
Figure 2. Fiber gasket showing over compression.
From the voice of the fluid sealing industry
Sealing SenSe
PuMPs & systeMs www.pump-zone.com May 2006 81
Gasket is mechanically damaged due to overhang of raised face or
flange bore
Withthistypeoffailure,itmaybeobviousthatthegasketisnotfittingproperlyintotheflange.
Review the gasket dimensions and compare them
withflangedetailtoverifygasketshavebeenproperlysized.Itisalsoimportanttoensuregasketsareproperlycenteredinthejointtoallowforuniformdistributionofstress.
No apparent gasket compression
achievedComparetheavailablecompressiveloadwiththerecom-
mendedloadfortheselectedgaskettype.Ifinsufficientloadisavailable,selectasoftergasketmaterial.
Withgasketsthatarerecessedinagroove,athickergasketmaybenecessary.Insomecases,itmaybepossibletoreducegasketareatoallowhigherseatingload.
Gasket is substantially thinner on OD than
IDThisconditionisindicativeofexcessiveflangerotation
orbending.The gasket dimensions should be altered to move
the
gasketreactiondiameterclosertotheboltstominimizebend-ingmovement.Itmaybenecessarytoprovideadditionalstiff-nesstotheflangebymeansofaddingback-uprings.Selectionofasoftergasketmaterialtolowerrequiredseatingstresses,orareductionofthegasketareatodecreaseseatingstressesmayalsobenecessary.
Gasket unevenly compressed around
circumferenceIfthegasketappearstobeunevenlycompressed,theinstal-
lationprocedureshouldbere-evaluated.Improperboltingup
maybetoblame.Also,makesurecertainsequentialboltupproceduresare
followed. ASME PCC-1 recommends using a
cross-patternorstarpatterntoapplytorqueinstagesandensurestressisapplieduniformlyacrossthegasket.
Gasket thickness varies periodically around circumference, with
compression higher near the bolt holes
Thisconditionisindicativeofflangebridgingbetweenboltsorwarpedflanges.
To correct the problem, provide reinforcing rings
forflangestobetterdistributeboltload.Italsomaybenecessarytoselectagasketmaterialwithalowerseatingstressorprovideadditionalbolts,ifpossible,toobtainbetterloaddistribution.If
flanges arewarped, re-machine the flanges or use a
softergasketmaterial.
It is important to remember thata leaky joint is a
jointfailure,notnecessarily indicativeof a gasket failure. A
jointconsistsofmatingflanges,bolts,andagasket.Specificationofthe
correct gasket design andmaterial for thepressure,
tem-perature,processfluid,flange arrangement, aswell
aspropergasketinstallationproceduresarevitaltothesuccessofthecon-nection.
Next Month: What factors should be considered when installing a
spiral wound gasket?
We invite your questions on sealing issues and will provide our
best effort answers based on FSA publications. Please direct your
ques-tions to: [email protected].
P&S
Fluid Sealing AssociationSealing Sense isproducedby theFluid
Sealing Associa-tion as part of our commitment to industry
consensustechnicaleducationforpumpusers,contractors,distribu-tors,OEMs,andreps.Asasourceoftechnicalinformationon
sealing systemsanddevices, and incooperationwiththe European
Sealing Association, the FSA also
sup-portsdevelopmentofharmonizedstandardsinallareasoffluidsealingtechnology.TheeducationisprovidedinthepublicinteresttoenableabalancedassessmentofthemosteffectivesolutionstopumpsystemstechnologyissuesonrationalTotalLifeCycleCostprinciples.
TheGasketdivisionoftheFSAisoneoffivewithaspecificproducttechnologyfocus.Aspartoftheirmissiontheydeveloppublications
such as theMetallic Gasketing Technical
Handbook,aswellasjointFSA/ESApublicationssuch asGuidelines for safe
seal usage - Flanges and Gas-kets and Gasket Installation
Procedures.Theseareprimersintendedtocomplementthemoredetailedmanufacturersdocumentsproducedbythemembercompanies.
ThefollowingmembersoftheGasketdivisionspon-sorthisSealing
Senseseries:
AdvancedEnergyTechnologyInc.
TheAsburyGraphiteMills,Inc.Chicago-WilcoxMfg.Co.
DaikinAmerica,Inc.DonitTesnitd.d.
DurablaCanada,Ltd.EmpakSpirotallicMexicanaSAdeCVTheFlexitallicGroup
GarlockSealingTechnologies
W.L.Gore&Associates,Inc.JohnCraneLamonsGasketCo.LapinusFibresInc.LattyInternationalS.A.SGLTechnicPolycarbonDivisionSimritDiv.ofFreudenberg-NOKSlade,Inc.TeaditInternationalTeijinTwaronUSA,Inc.ThermosealInc.YMT/Inertech,Inc.
