Ho Can i Troubleshoot Bolted Flange Conenction Leaks May06

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: sealingquestions@fluidsealing.com.

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.