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12/19/2014 Stress Analysis of underground Piping | What is Piping http://www.whatispiping.com/undergroundpiping 1/8 Underground or buried piping are all piping which runs below grade. In every process industry there will be few lines (Sewer or drainage system, Sanitary and Storm Water lines, Fire water or drinking water lines etc), part of which normally runs underground. However the term buried piping or underground piping, in true sense, appears for pipeline industry as miles of long pipe run carrying fluids will be there. Analyzing an underground pipe line is quite different from analyzing plant piping. Special problems are involved because of the unique characteristics of a pipeline, code requirements and techniques required in analysis. Elements of analysis include pipe movements, anchorage force, soil friction, lateral soil force and soil pipe interaction. To appreciate pipe code requirements and visualize problems involved in pipe line stress analysis, it is necessary to first distinguish a pipe line from plant piping. Unique characteristics of a pipe line include: High allowable stress: A pipe line has a rather simple shape. It is circular and very often runs several miles before making a turn. Therefore, the stresses calculated are all based on simple static equilibrium formulas which are very reliable. Since stresses produced are predictable, allowable stress used is considerable higher than that used in plant piping. High yield strength pipe: To raise the allowable, the first obstacle is yield strength. Although a pipe line operating beyond yield strength may not create structural integrity problems, it may cause undesirable excessive What is Piping An attempt to explain process piping engineering basics in detail to help all the process piping engineering professionals around the world. HOME ABOUT US PIPING STRESS PIPING SUPPORTS PIPING DESIGN FORUM PRIVACY POLICY CONTACT US MISC. 13th October 2014 want2learn Caesar II 1 Comment Basics for Stress Analysis of Underground Piping using Caesar II 2 Like 0 45 26

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  • 12/19/2014 StressAnalysisofundergroundPiping|WhatisPiping

    http://www.whatispiping.com/undergroundpiping 1/8

    Undergroundorburiedpipingareallpipingwhichrunsbelowgrade.Ineveryprocessindustrytherewillbefewlines(Sewerordrainagesystem,SanitaryandStormWaterlines,Firewaterordrinkingwaterlinesetc),partofwhichnormallyrunsunderground.Howeverthetermburiedpipingorundergroundpiping,intruesense,appearsforpipelineindustryasmilesoflongpiperuncarryingfluidswillbethere.

    Analyzinganundergroundpipelineisquitedifferentfromanalyzingplantpiping.Specialproblemsareinvolvedbecauseoftheuniquecharacteristicsofapipeline,coderequirementsandtechniquesrequiredinanalysis.Elementsofanalysisincludepipemovements,anchorageforce,soilfriction,lateralsoilforceandsoilpipeinteraction.

    Toappreciatepipecoderequirementsandvisualizeproblemsinvolvedinpipelinestressanalysis,itisnecessarytofirstdistinguishapipelinefromplantpiping.Uniquecharacteristicsofapipelineinclude:

    Highallowablestress:Apipelinehasarathersimpleshape.Itiscircularandveryoftenrunsseveralmilesbeforemakingaturn.Therefore,thestressescalculatedareallbasedonsimplestaticequilibriumformulaswhichareveryreliable.Sincestressesproducedarepredictable,allowablestressusedisconsiderablehigherthanthatusedinplantpiping.

    Highyieldstrengthpipe:Toraisetheallowable,thefirstobstacleisyieldstrength.Althoughapipelineoperatingbeyondyieldstrengthmaynotcreatestructuralintegrityproblems,itmaycauseundesirableexcessive

    What is PipingAnattempttoexplainprocesspipingengineeringbasicsindetailtohelpalltheprocesspipingengineeringprofessionalsaroundtheworld.

    HOME ABOUTUS PIPINGSTRESS PIPINGSUPPORTS PIPINGDESIGN FORUM

    PRIVACYPOLICY CONTACTUS MISC.

    13thOctober2014 want2learn CaesarII 1Comment

    Basics for Stress Analysis of UndergroundPiping using Caesar II

    2Like 045 26

  • 12/19/2014 StressAnalysisofundergroundPiping|WhatisPiping

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    deformationandpossibilityofstrainfollowup.Therefore,hightestlinewithaveryhighyieldtoultimatestrengthratioisnormallyusedinpipelineconstruction.Yieldstrengthinsomepipecanbeashighas80percentofultimatestrength.Allallowablestressesarebasedonlyonyieldstrength.

    Highpressureelongation:Movementofpipelineisnormallyduetoexpansionofaverylonglineatlowtemperaturedifference.Pressureelongation,negligibleinplantpiping,contributesmuchofthetotalmovementandmustbeincludedintheanalysis.

    Soilpipeinteraction:Themainportionofapipelineisburiedunderground.Anypipemovementhastoovercomesoilforce,whichcanbedividedintotwocategories:Frictionforcecreatedfromslidingandpressureforceresultingfrompushing.Themajortaskofpipelineanalysisistoinvestigatesoilpipeinteractionwhichhasneverbeenasubjectinplantpipinganalysis.

    Normallytheselinesdoesnothavehighdesigntemperatures(oftheorderof60to80degreecentigrade)andonlythermalstresscheckingissufficientforundergroundpart.CommonmaterialsusedforundergroundpipingareCarbonSteel,Ductileiron,castIron,StainlessSteelandFRP/GRP.

    InthisarticleIwilltrytoexplainthestepsfollowedwhileanalysingsuchsystemsusingCaesarII.Howeverthisarticledoesnotcoverthebasictheoryforanalysis.

    InputsRequiredforAnalysis:

    BeforeproceedingforanalysisofburiedpipingusingCaesarIIcollectthefollowinginformationfromrelateddepartment1.IsometricdrawingsorGAdrawingsofthepipelinefromPipinglayoutDepartment.2.Lineparameters(Temperature,Pressure,Material,FluidDensity,etc)fromprocessDepartment.3.SoilPropertiesfromCivilDepartment.

    CaesarIIforUndergroundPipingAnalysis:

    TheCAESARIIundergroundpipemodelerisdesignedtosimplifyuserinputofburiedpipedata.ToachievethisobjectivetheModelerperformsthefollowingfunctionsforanalyst:

    Allowsthedirectinputofsoilproperties.TheModelercontainstheequationsforburiedpipestiffnessesthatareoutlinedlaterinthisreport.Theseequationsareusedtocalculatefirstthestiffnessesonaperlengthofpipebasis,andthengeneratetherestraintsthatsimulatethediscreteburiedpiperestraint.

    Breaksdownstraightandcurvedlengthsofpipetolocatesoilrestraints.CAESARIIusesazoneconcepttobreakdownstraightandcurvedsections.Wheretransversebearingisaconcern(nearbends,tees,andentry/exitpoints),soilrestraintsarelocatedincloseproximityandwhereaxialloaddominates,soilrestraintsarespacedfarapart.

    Allowsthedirectinputofuserdefinedsoilstiffnessesonaperlengthofpipebasis.Inputparametersincludeaxial,transverse,upward,anddownwardstiffnesses,aswellasultimateloads.Userscanspecifyuserdefinedstiffnessesseparately,orinconjunctionwithCAESARIIsautomaticallygeneratedsoilstiffnesses.

    ModelingstepsfollowedinCaesarII:

    Themodelingofburiedpipingisveryeasyifyouhaveallthedataatyourhand.Thefollowingstepsarefollowedformodeling:

    Fromtheisometricmodelthelineinthesamewayasyoufollowincaseofabovegroundpipemodeli.e,enterlinepropertiesinCaesarSpreadsheet,enterlengthsbybreakingthelineintoseveralnodesorselectanexistingjobforconvertingitintoanundergroundmodel.

  • 12/19/2014 StressAnalysisofundergroundPiping|WhatisPiping

    http://www.whatispiping.com/undergroundpiping 3/8

    AnalystcanstarttheBuriedPipeModelerbyselectinganexistingjobandthenchoosingInputUndergroundfromtheCAESARIIMainMenu.TheModelerisdesignedtoreadastandardCAESARIIinputdatafilethatdescribesthebasiclayoutofthepipingsystemasifitwasnotburied.FromthisbasicinputCAESARIIcreatesasecondinputdatafilethatcontainstheburiedpipemodel.Thissecondinputfiletypicallycontainsamuchlargernumberofelementsandrestraintsthanthefirstjob.Thefirstjobthatservesasthepatternistermedtheoriginaljob.Thesecondfilethatcontainstheelementmeshrefinementandtheburiedpiperestraintsistermedtheburiedjob.CAESARIInamestheburiedjobbyappendingaBtothenameoftheoriginaljob.

    WhentheBuriedPipeModelerisinitiallystartedup,thefollowingscreenappears:

    Fig.1:SampleCaesarIISpreadsheetforBuriedPiping

    Thisspreadsheetisusedtoentertheburiedelementdescriptionsforthejob.Theburiedelementdescriptionspreadsheetservesseveralfunctions:

    Allowsanalysttodefinewhichpartofthepipingsystemisburied.

    Allowsanalysttodefinemeshspacingatspecificelementends.

    Allowstheinputofuserdefinedsoilstiffnesses.

    From/Tonode:

    AnyelementofpipeinCAESARIIcanbedefinebytwoelementsfirstisstartpointandsecondisendpoint.Inburiedpipemodel,beforeconversiontheFrom/Tonodesremainssameasunburiedmodel.

    Soilmodelno.:Thiscolumnisusedtodefinewhichoftheelementsinthemodelareburied.Anonzeroentryinthiscolumnimpliesthattheassociatedelementisburied.A1inthiscolumnimpliesthattheanalystwishestoenteruserdefinedstiffnesses,onaperlengthofpipebasis,atthispointinthemodel.Thesestiffnessesmustfollowincolumnnumbers6through13.Anynumbergreaterthan1inthesoilmodelno.columnpointstoaCAESARIIsoilrestraintmodelgeneratedusingtheequationsoutlinedlaterunderSoilModelsfromanalystenteredsoildata.

    From/Tomeshtype:AcriticalpartofthemodelingofanundergroundpipingsystemistheproperdefinitionofZone1bearingregions.Theseregionsprimarilyoccur:Oneithersideofachangeindirection

  • 12/19/2014 StressAnalysisofundergroundPiping|WhatisPiping

    http://www.whatispiping.com/undergroundpiping 4/8

    ForallpipesframingintoanintersectionAtpointswherethepipeentersorleavesthesoilCAESARIIautomaticallyputsaZone1meshgradientateachsideofthepipeframingintoanelbow.NoteitistheanalystsresponsibilitytotellCAESARIIwheretheotherZone1areasarelocatedinthepipingsystem.

    Userdefinedstiffness&ultimateload:Thereare13columnsinthespreadsheet.Column6to13carrytheuserdefinedsoilstiffnessesandultimateloadsifanalystdefinessoilmodel1.Analysthastoenterlateral,axial,upward,downwardstiffnesses&loads.

    Procedure:

    1. Selecttheoriginaljobandentertheburiedpipemodeler.Theoriginaljobmustalreadyexist,andwillserveasthebasisforthenewburiedpipemodel.Theoriginalmodelshouldonlycontainthebasicgeometryofthepipingsystemtobeburied.Themodelerwillremoveanyexistingrestraints(intheburiedportion).Addanyundergroundrestraintstotheburiedmodel.RenametheburiedjobifCAESARIIdefaultnameisnotappropriate.

    2. EnterthesoildatausingSoilModels.

    3. Describethesectionsofthepipingsystemthatareburied,anddefineanyrequiredfinemeshareasusingtheburiedelementdataspreadsheet.

    4. ConverttheoriginalmodelintotheburiedmodelbytheactivationofoptionConvertInput.Thisstepproducesadetaileddescriptionoftheconversion.

    5. ExittheBuriedPipeModelerandreturntotheCAESARIIMainMenu.Fromheretheanalystmayperformtheanalysisoftheburiedpipejob.

    Thestepstocreatesoilmodelandfewotherimportantconsiderationswillbepublishedinfuturepostsonundergroundpipinganalysis.

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    4. StressAnalysisofColumnpipingsystemusingCaesarII

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    StarSaturday20September2014,1:13am

    Ireadalotofinterestingarticleshere.Probablyyouspendalotoftimewriting,

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