a brief presentation on storage tanks

2/24/2015 ABriefPresentationonStorageTanks|WhatisPiping

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AStorageTankisastaticequipmentwhichisusedtostoreproducts(liquids)inatmosphericpressureconditions.StorageTankscanbesplitintotwotypes

SitebuiltTanks

SmallerTanks(transportedtositefullyassembled)

Ingeneralsitebuilttanksaredesignedasverticalcylindershoweversmallertanksmaybeeithervertical/horizontalcylindersorrectangular/squareinshape.

LargeStorageTanksareconstructedonsite,onpreparedfoundationsastheyaretoolargetotransport.

Toreducesiteworkandtheamountofequipmentrequired,thecomponentpartsofthetankarenormallyprefabricatedorpreformedpriortodelivery.

Application:

RefineryandPetrochemical

Fertilizer

What is PipingAnattempttoexplainprocesspipingengineeringbasicsindetailtohelpalltheprocesspipingengineeringprofessionalsaroundtheworld.

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12thNovember2013 want2learn DetailDesign 1Comment

A Brief Presentation on Storage Tanks

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OilandGas

Chemical

TypeofStorageTank(Fig.1):

StorageTankscanbedefinedintothreetypes

ConeRoofStorageTank:AConeRoofStorageTankhasverticalsidesandisequippedwithafixedconeshapedroofthatisweldedtothesidesofthetank.

OpenTopFloatingRoofStorageTank:AnOpenTopFloatingRoofStorageTankissimilartotheconerooftankinconstructionbutwiththeexceptionthatithasnofixedroof.Apontoontyperooffloatsdirectlyontheflammableliquidsurface.

InternalFloatingRoof/CoveredFloatingRoofStorage:AnInternalFloatingRoof/CoveredFloatingRoofStorage(seereddome)Tankisacombinationofboththeconeroofordomeandtheopentopfloatingrooftank.Thetankhasaconeroofbutwiththeadditionofaninternalfloatingrooforpanthatfloatsdirectlyonthefuelsurface.

Fig.1:ConeRoofandfloatingRoofStorageTank

LocationofStorageTanks:

StorageTanksaremostlylocatedinsideaTankFarmareainsideabundedarea(Fig.2).

Bundedareaisnecessaryaroundstoragetankwhenthepotentialenvironmentalandeconomicriskoftankspillageisgreat.Itsfunctionistocontainspillagesothatsubsequentdamagetoadjacenttanksandsurroundingareascanbeminimised.



Fig.2:TanklocationinsideBundArea

ComponentofStorageTanks:

TypicallyaTankconsistsofthreecomponents(Fig.3).

Shell:Acylindricalportionwhichisrestingonthebottomplateandcoveredbytheroof.

BottomPlate:Aweldedflatbottomplatewhichisplacedbeneaththecylindricalshell.

Roof:Thefixedrooftankismostlyprovidedwithaconicaltoproof.Largerdiameterconicalrooftanksaresupportedbyroofstructuresorcolumnsandtheopentoptankismostlyprovidedwithafloatingroof.

Fig.3:ComponentsofaStorageTank

ConstructionofTankShell:

Tankshellisconstructedbybuttweldingsteelplatesofspecifiedlengthandwidthatthereedgesinordertoformacylindricalshell.

ConstructionofTankBottom:

Thebottomofatankisconstructedfromflatplates.Platesarearrangedwithrectangularplatesinthecentreandsketchplates(cuttosuitradius)aroundtheperimeter.



ConstructionofTankRoof:

Thetopofatankisconstructedfromflatplates.Platesarearrangedwithrectangularplatesinthecentreandsketchplates(cuttosuitradius)aroundtheperimeter.

TypeofRoofSupportStructures:

FixedConicalorDomerooftanksareprovidedwithinternalraftersortrusses(Fig.4).

SomelargerdiameterConicalorDomerooftanksarealsoprovidedwithcolumnsupports.

Fig.4:VarioustypesofroofSupports

InternationalDesignCodesforSiteBuiltStorageTanks:

Themaindesigncodesforverticalcylindricaltanksare:

BSEN14015:2004VerticalSteelWeldedStorageTankswithButtWeldedShellsforthePetroleumIndustry

API650WeldedSteelTanksforOilStorage

DEP34.51.01.31GenandDEP64.51.01.31Gen

DesignAspectsofTank:

Thedesignaspectsofthetankcanbedividedintothefollowing:

Designstandards:ThetankcanbedesignedbyusingdifferentInternationalstandardsasAPI650andBSEN14015.

PlateSize:Althoughthephysicalsizeoftheshellplatesisafunctionoftheheightanddiameterofthetank,theactualsizeisalsodependentuponmaterialavailability,fabricatorsfacilitiesandhandling/logisticissues.Alargeplateisthemoredifficulttoformandtohandle,howeveralargeplaterequireslessweldingduringtankerection.Theplatesizemustthereforebeconsideredonacasebycasebasistoachievethemosteconomicaldesign.Forexample,fora10mhightank,themostpracticalandeconomicalplatewidthwouldbe2.5msoastoachievefourshellcourses.Plates3.33mwidearelargeandnonstandard.

LoadingConditions:

External/Internal:Externalloadsonatankmayresultfromadjoiningpipingorstructures.Theseloadsmaybeduetoforexampletheirstaticweightorasaresultofthermalgrowth.Duetotheuseofrelativelythinandthereforeflexiblesteelplates,tankshaveapoorabilitytoresistexternalloadsandthereforemeasuresshouldbetakentominimizeallexternalloads.MethodstoanalyzeexternalpipeloadscanbefoundinAPI650.



Wind/Earthquake:Windandearthquakeloadsdependgreatlyontheenvironmentalconditionsoftheproposedsite.Guidanceonhowtoanalyzewindandearthquakeloadscanbefoundintheappropriatedesigncodeshoweverparticularattentionshouldalsobegiventotheriskofwindandearthquakesduringtankerectionwherethefullstabilityofthetankisnotyetavailableandtemporaryfacilitieshavetobedeployed.

Pressure/Vacuum:Althoughthemaximumexternaldesignpressureoftanksisverylow(6mbar),itshouldbenotedthattanksareinherentlyverypooratresistingpartialvacuums.Caremustbetakentoensurethatvacuumbreakervalvesarecorrectlysizedtopreventapartialvacuumformingduringforexampleliquiddrawoff/draining.Seebelowslideforanexamplephotographofatankcollapseduetovacuum.

Foundations:Althoughafabricatedtankisrelativelylightforitsphysicalsize,duetothestaticheadfromtheliquidcontentstheoverallloadontothefoundationscanbeconsiderable.Thedesignofthefoundationsisespeciallyimportantwherethegroundconditionsaresoftorinconsistentwhichcouldresultintheriskofsinkingorunevensettlementwhichcouldcausefailureofthetank.Topreventthisproblemoccurringitisimportantthatasoilsurveyoftheproposedsiteisperformedearlyintheprojectandthefoundationsdesignedtosuit.Thisanalysismaybeperformedbyacivilengineeringcontractor.

Ontankswherethereisapotentialforupliftcausedbyforexamplewindloading,thebaseofthetankshouldbeanchoredtothegroundusingfoundationbolts.Thisisnormallydonebyprovidingaconcreteringbeamaroundtheperimeterofthetank.Onsmallertankstheentirefoundationmaybemadefromreinforcedconcretehoweverduetothecost,aringbeamismoreeconomical.Upliftcanalsoresultfrominternalpressurebowingthefloorwhenemptyandhighpressuretanksshouldalwaysbeprovidedwithfoundationbolts.Theareaunderthetankflooristypicallycompactedgroundcoveredwithalayerofbitumencoatedsandwhichhelpsbeddinginofthefloorplatesandasameansofcorrosionprotection.

Layout:Layoutoftanksdependsuponanumberofparameterssuchasnumberoftanks,groundconditions,processdutyetc

Exampleofvacuumcollapse(Fig.5):

Thiscollapseoccurredfollowingaccidentaldrainingofthecontentswhilstthevacuumvalvewasblockedbyplastictapeduringpaintrefurbishment.



Fig.5:ExampleofVacuumCollapse

MaterialofConstruction:

Carbonsteel

StainlessSteel

DuplexStainlesssteel

TypicalMethodofTankErection:

Therearefourmainmethodsoftankerection:

Progressive

CompleteAssembly

Jacking

Flotation

Progressiveassemblyandwelding:Intheprogressiveassemblymethod,thebottomplatesareassembledandweldedfirst.Thereaftertheshellplatesareerected,heldinplace,tackedandcompletelywelded.Thisshallbedonecoursebycourse,workingupwardstothetopcurbangle.Nocourseshallbeaddedaslongasthepreviouscoursehasnotbeenentirelywelded.Theerectionandcompletionoftheroofframingandroofplatesthenfollow.

Completeassemblyfollowedbyweldingofhorizontalseams:Inthecompleteassemblymethod,thebottomplatesareassembledandweldedfirst.Thereaftertheshellplatesareerected,heldinplace,tackedandonlytheverticalseamscompletelywelded,leavingthehorizontalseamsunwelded.Thisshallbedonecoursebycourse,workingupwardstothetopcurbangle.Nocourseshallbeaddedaslongastheverticalseamsofthepreviouscourse



havenotbeenentirelywelded.Theerectionandcompletionoftheroofframingandroofplatesthenfollow.Finallythehorizontalseamsarewelded,workingupwardsfromthebottomcourseordownwardsfromthetopcurbangle.

Jackingupmethod:Somecontractorsemployasystemoferectioninwhichthebottomplatesarecompleted,Thetopcourseiserectedonthebottomplates,theroofframingandsheetingarecompletedandanumberofjacksarethenassembledaroundthestructure.Bymeansofthesejacks,thecompletedtopcoursetogetherwiththeroofframingandsheetingisliftedtoaheightsufficienttoinsertthenextlowercourse.Thejackingmethodandthesupportingofthepartlyerectedshellshallhavenoadverseeffectontheroundnessoftheshell.Theweldingiscompletedateachstageofliftuntilallcoursesoftheshellplateshavebeeninsertedandthefinishedheightisreached.Thefinaloperationistheweldingofthebottomcoursetothebottomplates.

Flotationmethod:Theflotationmethodisusedforfloatingrooftanks.Afterthecompletionofthebottomplatinganderectionandweldingofthetwolowercoursesofthetank,thefloatingroofisassembledonthetankbottomandcompleted.Thetankisthenfilledwithwaterand,usingthefloatingroofasaworkingplatform,thethirdandsubsequentcoursesareerectedandwelded,waterbeingpumpedinaseachcourseiscompleted.Regularchecksontheverticalalignmentandroundnessarerequired.ThismethodmayonlybeusedatlocationswheresoilsettlementisverylimitedandwiththeagreementofthePrincipal.Thepredictedsoilsettlementsofthesoilinvestigationreportshallbetakenintoaccount.Asmallcraneisusuallyerectedonthefloatingroofforhoistingtheshellplatesintoposition.

TankFoundations(Fig.6):

Tanksareusuallysupportedonconcreteringwallfoundationorpadtypefoundation.



Fig.6:TankFoundations

Venting:

Ventingisveryimportantduetothelowdesignpressureoftanks.Theymustconsider:

In/outflowoftank

Thermalventing

Numberofindependentbreathervalves

Birds/blockage

RoofProfile

Floatingrooftankshaveminimumventlosses

Considerationmustbegiventothemaximuminflowintothetank(causingoverpressurisation)andalsothemaximumoutflow(causingpartialvacuum).Thesemayresultfromtheactionofpumpsand/orprocessupsetssuchasgasblowbyfromavessel.

Thetypeandselectionofthereliefvalvesalsodependsuponifthereisavapourblanketwithinthetank.Forexamplethismaybenitrogenorfuelgas.Fuelgasshouldnotbeventedtotheatmosphereandwherepracticalshouldinsteadberecovered.



Tanksarealsoprovidedwithsimpleemergencyvents(blowoutcovers),thepurposeofwhichistopreventtankdamageintheeventofforexampleaprocessupsetcondition.

Tankroofsareinherentlydesignedtobeweakerthantheshellsothatintheeventofoverpressurisationandthefailureoftheventingsystem,theroofwillfailandtheshellwillremainintactthuspreventingspillage/lossofthecontents.

SmallTanks

SmallerTanks,definedhere,asthosetransportedtositefullyassembledmaybecylindricalorrectangularinshape.

Theyareusedformanypurposessuchas:

Waterstorage

Fuelstorage

Settlingorseparationoffluids(e.g.oilywatertreatment)

Lubricationoilstorage

Chemicalstorage

Drainstanks

Smalltankscanbesuppliedasindividualitemstositeormorecommonlytheyaresuppliedonpackagedskids.

Tanksmayalsobefabricatedfromconcrete.

RectangularTanks

Theseareverycommononpackagedskidsastheyofferthegreatestvolumewithinaconfinedpackagespaceenvelope.

Forexample:

Lubricationoiltanksonpump/compressorskids

Chemicalstorageonchemicalinjectionskids

Thereisnodefinitivedesignstandardforrectangulartanksandtheyareusuallydesignedfromfirstprinciplesorgoodengineeringpractice.

Rectangulartanksmaybemadefromflatorcorrugatedplates.Dependingonthetankssize,flatplatesarenormallyprovidedwithinternalorexternalstiffenerstopreventplatedeflection.

Rectangulartanksareoftenprovidedwithinternalpartitionplatessothattwoormoreseparatestoragevolumesareprovidedwithinacompactarrangement.



Duetothelargeamountofstiffeningrequired,itisnoteconomictomakerectangulartanks.Insuchcasesalternativedesigns,suchasacylinder,shouldbeconsidered.

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