1 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. DESIGN AND MAINTAINANCE OF STORAGE TANKS FOR HSD MAIN PROJECT REPORT Submitted by: MUHAMMED SHAFEEQUE PRASOON KUMAR K.P MUHAMMED JAWAD ABINRAJ P.K SHADIL N.K GUIDE:Mr.BALAGOPAL Sr. Engineer Maintenance Department BPCL KOCHI DEPARTMENT OF MECHANICAL ENGINEERING AWH ENGINEERING COLLEGEKUTTIKKATOOR, CALICUT, KERALA 2013 2 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. ACKNOWLEDGEMENT First of all we would like to thank God the Almighty for the divine grace bestowed on us to complete this project successfully on time. We express our sincere thanks to Prof. JUSTIN DICOTTU (Head of the DepartmentofMechanicalEngineering,AWHENGG.COLLEGE)for givingusthisopportunitytopresentthisprojectandforthefacilities offered to us throughout this endeavor. The main motivation and driving force behind this project is our external guideMr.BALAGOPAL(Sr.EngineerE&CDepartmentofDepartment of BPCL). We are unboundedly grateful to him for the timely corrections andscholarlyguidance,whichmadeusconfidentenoughtocomeout successfully. We also thank Mr. SARUN (Asst. Engg.E&C Department of BPCL) for his support and guidance throughout the completion of our project.WeextendourheartythankstoourinternalguideSir.JITHU PAUL(Lecturer,DepartmentofMechanicalEngineering,AWHENGG. COLLEGE)forhisenterprisingattitudeandsupportthatmadeour project fruitful. We express our sincere thanks to all the faculty members of the Mechanical Engineering Department for their co-operation. 3 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. ABSTRACT Petroleum storage tank is an indispensable part of petroleum refining industries.Theyareusedforintermediateandfinalproductstoragein processplantorforstoringpetroleumproductsandchemicalsatterminals. Theyareusedformixing,blending,precipitationandsettingprocessoras chemical reactor vessels. Storage tanks are different types such as cone roof, floatingroof,floatingcumconeroofandsphericalvessels.Forstoring motor spirit/ High Speed Diesel (HSD) we use floating roof tanks. As safety has the prime importance in a refinery different fire fighting equipments are designed and installed. Along with thisthorough inspection procedures and maintenancearenecessarytoensurebettersafety.Allthepetroleum refineriesaremainlyconcentratingonthestoringofvariousproducts because of efficient storage and better safety, the designing of storage tank is highly important. 4 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. CONTENTS 1.Company Profile 1 2.Introduction to Storage Tanks... 4 3.Types of Storage Tanks. 5 4.Parts of Storage Tanks. 12 5.Material Specifications for Storage Tank 20 6.Design of Storage Tank... 227.Inspection of Storage Tank.55 8.Testing of Storage Tank.63 9.Conclusion..67 10. References68 5 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. COMPANY PROFILE KochiRefinery,aunitofBharatPetroleumCorporationLimited(BPCL), embarkedonitsjourneyin1966withacapacityof50,000barrelsperday. FormerlyknownasCochinRefineriesLimitedandlaterrenamedasKochi RefineriesLimited,therefinerywasoriginallyestablishedasajointventurein collaborationwithPhillipsPetroleumCorporation,USA.Todayitisafrontline entity as a unit of the Fortune 500 company, BPCL. Kochi Refinery, located at Ambalmugal near the city of Kochi in Kerala, is one of the two Refineries of BPCL, presently having a crude oil refining capacity of 9.5 Million Metric Tones per Annum (MMTPA). The product portfolio of the 190,000 barrelsperdayrefinerytodayincludespetrochemicalfeedstockandspecialty products in addition to its range of quality fuels. FuelproductsofthisfuelbasedrefineryincludesLiquefiedPetroleumGas, Naphtha, Motor Spirit, Kerosene, Aviation Turbine Fuel, High Speed Diesel, Fuel OilsandAsphalt.SpecialtyproductsforthedomesticmarketsincludeBenzene, Toluene, Propylene, Special Boiling Point Spirit, Poly Iso Butene and Sulphur. Therefineryhasimplementedworldclasstechnologyandsystemsforoperations and enterpriseresource planning. It is an ISO 14001 EnvironmentalManagement Systems(EMS)andISO9001:2000QualityManagementSystem(QMS) accreditedcompanyandhasalsoobtainedtheISO17025(TestingMethodsin QualityControl)certificationfromNABL(NationalAccreditationBoardfor testing & Calibration of Laboratories). The refinery has successfully implemented the Occupational Health and Safety Management System (OHSAS) 18001:2007 in the year 2009. WiththeprestigiousCrudeOilreceiptfacilitiesconsistingofthe SinglePoint Mooring (SPM) and the associated shore tank farm in place since December 2007, therefineryisequippedtoreceivecrudeoilinVeryLargeCrudeCarriers (VLCCs).ThisfacilityhelpsKochirefineryinreducingthefreightchargestoa greatextent,overandaboveincreasingflexibilityincrudeoilselection.This, thereby, is a major infrastructure facility to accelerate the future growth of Kochi Refinery. Therefineryhasfacilitiestoevacuateproductstotheconsumingcentersthrough road,rail,shipsandthroughpipelines.Allthemajorindustriesintheareaare connectedtotherefineryforproductreceipt.TheBPCLinstallationat 6 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Irumpsanam, to which the refinery is connected by pipelines, is the major product distributioncentreoftherefinery.PetronetCCK,ajointventurecompanyof BPCLlooksafterthe300kmlongpipelinethatconnectstherefinerytovarious consumption points in Tamil Nadu such as Coimbatore and Karur. Ofthetwo-partCapacityExpansioncumModernizationProject(PhaseII),the capacity expansion to9.5 MMTPA hasbeensuccessfully completed and refinery modernizationslatedforcompletioninAugust2010wouldequiptherefineryto produce auto-fuels conforming to Euro-III and partly Euro-IV specifications. The refinerys foray into direct marketing began since 1993 through marketing of itsaromaticproducts-BenzeneandToluene.Theentryintotheinternational petroleumbusinessstreambeganwithitsfirstparcelofFuelOilexportedin January2001.Sincethentherefinery,hasearnedthereputationasareliable player in the international trade, by virtue of superior product quality and customer service. Moreover, the Fuel Oil has been benchmarked in the Singapore and Dubai Fuel Oil markets. KochiRefineryissituatedinKochi,themosthappeningcityinKeralathatis rightlycalledGodsowncountry.Therefineryhasauniquebondwithits environmentwhichisevidentinthegreenblanketsocarefullynourishedright aroundit.Therefineryhasbeenblessedwithafinetopographyandtheentire complex,spreadingacrossoverthousandtwohundredacreshasbeenso constructed as to blend naturally with it. Upcoming expansions and developments wouldalsoadheretothisphilosophyofblendingwithnature.Themostrecent addition to the refinery architecture is the rainwater harvesting pond and eco-park thathasbeenconvertedtoamust-seespotwithsprawlinglandscapedlawnsand thatchedcanopiesforconferencesandget-togethers.Yearafteryeartherefinery hasbeenbaggingaccoladesforitscommitmenttotheenvironment;fortheall round care for the environment, the judicious storage, use and reuse of water, the efficiencyinmanagingsolidwastesandeffluentsandthecaretakentokeepthe atmosphere clean. The recent achievement of 24 million accident free man-hours stands testimony to thefactthattheprimefocusofKochiRefineryisonsafetyineverythingwedo. Fromtrainingtoretraining,andadheringtointernationalstandardsinsafety practices,both,offsiteandonsite,KochiRefineryhastakenitasamissionto make safe living and working a natural mantra of its employees, contract workers, customersandthegeneralpublic.Severalawarenessprogramshavebeen successfully conducted to this effect with the results for all to see. 7 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Asasociallyresponsiblecorporatecitizen,thecommunitywelfare initiatives of the refinery concentrate on developing the weaker sections of society, particularly,thescheduledcastesandscheduledtribesandpeoplebelowthe povertylineinimportantsectorslikehealth,education,housingandwomen empowerment.Mostoftheprogramsfallingunderthecategoriesofmedicaland educationalassistanceturnedouttobepovertyalleviationmeasuresalso.Thisis since the programs like universal health insurance, scholarship to SC/ST students and medical camps for poor have helped the poor villagers in the refinery vicinity to savemoneyover their medical expenses and educational expenses of children. Variouspeopleintensivesmall-schemecommunitydevelopmentprogramshave brought new life for many; be it poor villagers in need of medical treatment; poor students in government schools or differently abled children! Thus,apartfrommaintainingitsworldclassstandardsinoperational excellence, the singular objective of Kochi Refinery is to uphold the BPCL vision ofenergizinglivesbycontinuedexcellenceinallroundperformancewithnew ideas, added vigor and sustained commitment to its social, cultural, organizational and natural environment. Process KochiRefinerypresentlyhasacrudeoilprocessingcapacityof9.5MMTPA (MillionTonsperAnnum)initstwoCrudeDistillationunits(CDU-1andCDU-2).Therefinerycurrentlyprocessesabout30%ofIndigenousand70%Imported crude oils. Crude oil is transported in ships from the point of origin to Kochi and is receivedthroughaSinglePointMooring(SPM)facility.KochiSPM,located approximately 20kmsoff the shore of Puthuvypeen, is capable of handling Very largeCrudeCarriers(VLCC)withcrudeoilcarryingcapacitiesupto3.0Lakh Tons.CrudeoilfromSPMisreceivedinoffshoretanksinPuthuvypeenandis then pumped to the refinery. Apart from the Crude Distillation Units, major processing facilities in the refinery include a Fluidized Catalytic Cracking (FCC) unit, Diesel Hydro Desulphurization (DHDS)unit,KeroseneHydroDesulphurization(KHDS)unit,SulphurRecovery Unit (SRU) and an Aromatics Block consisting of a Naphtha Splitter Unit (NSU), NaphthaHydroDesulphurization(NDHS),CatalyticReformerUnit(CRU)and Aromatics Recovery Unit (ARU). 8 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. INTRODUCTION TO STORAGE TANKS Petroleum storage tank are an indispensable part of petroleum refining industries. Theyareusedforintermediateandfinalproductstorageinprocessplantorfor storingpetroleumproductsandchemicalsatterminals.Theycanalsobeusedas process equipment in non-ferrous plants where open top tanks are used for mixing, blending, precipitation and setting process or as chemical reactor vessels. Tanks are classified according to their construction, and the construction is on the basis of the product which is to be stored in them. CLASSIFICATION OF PETROLEUM PRODUCTS Petroleum products are classified on the basis of their Flash Points. FLASH POINT FlashPointofanypetroleumliquidstheminimumtemperatureatwhichthe liquid yields vapor in sufficient concentration to form an ignitable mixture with air and gives a momentary flash on application of a smell pilot flame under specified conditions of test. Petroleum products are classified according to their flash pints as follows: Class A Petroleum Liquidswhichhaveflashpointbelow23degreeC-crude(BombayHigh), gasoline, naphtha, low aromatic naphtha, high aromatic naphtha. Class B Petroleum Liquidsthathaveflashpointof23degreeandabovebutbelow65degreeC-superior kerosene oil , high speed diesel, light diesel oil, aviation turbine fuel, and jet propulsion -5. 9 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Class C Petroleum Liquidsthathaveflashpointof65degreeCandabovebutbelow93degreeC-furnace oil, low sulphur heavy stock, asphalt, seal oil, plant fuel. Excluded Petroleum Liquidsthathaveflashpointof93degreeCandaboveliquefiedgasesincluding LPG do not fall under this classification but from separate category. CLASSIFICATIONOF STORAGE TANKS 1.Cone roof tanks 2.Floating roof tanks 3.Floating cum cone roof tanks 4.Spherical vessels 1.CONE ROOF TANKS The cone roof tanks have fixed and are in a sense closed vessels. They are vertical cylindrical vessels having a conical top and made of welded steel plates and used mainlyforstoringlessvolatileproducts.Tanksmeantforstoringproductslike 9 March 2009 BPCL Kochi Refinery 13FIXED ROOF TANKFOUNDATIONSHELLBOTTOMPLATECONE ROOFVENT10 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. asphalt, vacuum gas oil etc. at high temperature is fully insulated externally. There are 43 cone roof tanks in BPCL at present. Depending on the service the cone roof tanks will have the following accessories. FLOATING ROOF TANKS Floatingrooftanksareintendedforstoringproductshavinghighvaporpressure like HSD and gasoline. They have a movable roof that floats on the surface of the tankcontents.Thusthevaporspaceiskeptconstantandminimum.Roofsare pontoontypehavingenclosedairchambers.Foamtypeneoprenesealoffthe clearance between the rim of the roof and the tank shell these tanks. As long as the pontoonsdonotleaktheroofwillnotsink.Theroofissupportedwhenitisnot afloat by a number of adjustable legs with low and high position. Normally roofs are kept on low legs.When a tank is to be taken out of service for cleaning or repairs, the roof has to be put on high legs toprovide space for people to work inside. Pump out vents in the roof permitthe escape of air when an empty or near-empty tank is filled and the roofis afloat. Roof drains are provided to drain water that is collected on the roof during rains. This is done by providing hoses or pipes with swivel joints from the 11 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. rooft0theoutsideofthetankshellnearthebottom.Anon-returnvalveonthe hose/pipe at the roof end and a gate valve at the bottom prevent escape of oil from thetankincasethehosedevelopsleak.Incertaincasetheroofisalsoprovided withanemergencydrainhavingwaterseal.Incasestherainwaterdoesnotflow freely through the roof drain it can get into the tank through the emergency drain. Access to the floating roof is by an inside stairway, one end if which is hinged at the gauges platform at the top of the outside stairway and the otherend is free to move on rollers on a runway fixed to the roof as the roof moves up and down to maintaintheshapeofthetankwhenitissubjectedtowindloadsthetankis reinforced with stiffening rings called wind girders. Thereare71floatingrooftanksinBPCLatpresent.Thefollowingarethe accessories provided on floating roof tanks: Man ways to go inside the shell and over the roof Gauging datum plate Gauge hatch with cover and reference mark Dial thermometer Mixing devices Water draw Roof drain Inlet pipe header with jet nozzle and outlet Gas fired burners with steam heating coil for heating the product Outside stairway Inside stairway 12 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. 9 March 2009 BPCL Kochi Refinery 19FLOATING ROOF TANKFOUNDATIONSHELLBOTTOMPLATEPONTOONROOF DECKSUPPORT LEG13 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. FLOATING CUM CONE ROOF TANKS They have fixed cone roof in addition to a floating roof and they are intendedfor storingtoxicproductshavinghighvaporpressure.Productslikebenzeneand toluenearecarcinogenicandshouldbepreventedfromescapingintothe atmosphere.Sotheyarestoredinfloatingcumconerooftanks.Thesetanks preventproductfromcontaminationandareusedtostoreclassAandclassB products. There are 13 floating cum cone roof tanks in BPCL at present 9-Mar-09 13FOUNDATIONSHELLBOTTOMPLATECONE ROOFROOF DECKSUPPORTLEGFLOATING CUM FIXED ROOFFLOATING CUM FIXED ROOF TANK TANK14 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Grouping of Tanks Groupingofpetroleumproductsforstorageshallbebasedonproduct classification. Class A and/or class B petroleum can be stored in the same typeoftanks.ClassCpetroleumshouldbestoredseparateenclosure. However,whereclassCpetroleumisstoredinacommondykealong withclassAand/orclassBpetroleum,allsafetystipulationsapplicable for class A and/or class B respectively shall apply.Excluded petroleum shall be stored in a separate dike enclosure and shall not be stored along with class A, B or C petroleum.Tanksshallbearrangedinmaximum2rowssothateachtankis approachableformtheroadsurroundingtheenclosure.However,tanks having capacity 50000 cum and above shall be laid in single row. Inter-distances for tanks/offsite facilities Thefollowingstipulationsshallapplyfortheinter-distancesforaboveground tanks storing petroleum: Inter distance for storage tanks 15 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Sl.NoItemFRTCRT (ClassA&B Petroleum) Class Petroleum 1.Alltankswith diameter upto 50m (D+d)/4(D+d)/4(D+d)/6 2.Alltankswith diameter exceeding 50m (D+d)/4(D+d)/3(D+d)/4

16 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. PARTS OF STORAGE TANK BOTTOM PLATES AND ANNULAR PLATES Bottomplatesarethoseplateswhicharelaidatthebottomofthetank.These plates are lap welded to each other.Allbottomplateshaveanominalthicknessof6mmexcludingofcorrosion allowance specified by the purchaser. Bottom plates get corroded rapidly if the fluid is having sea water content (crude petroleum). Bacterial corrosion of the bottom plates is generally observed in crude andHSDtankshavinghighsulphurcontent.Thebottomplatesdevelopdeep isolatedpitswhicheventuallypunctureandbottomstartsleaking.Sotheproper corrosion allowance should be provided. Annularplatesarethoseplatesonwhichtheshellplatesrest.Annularplates shouldbecapableofwithstandingtheweightoftheshellplatesandthe appurtenance. AccordingtoAPI650(3.5)11thedition2007,annularplatesshallhavearadial width that provides at least 600mm between the inside of the shell, any lap welded joint in the remainder of the bottom shall have at least a 36mm projection outside fromtheshell.Theprojectingoutportionoftheannularplatesisproneto corrosionattheedgesduetoaccumulationofwaterbetweenthefoundationand the annular plates. So here also appropriate corrosion allowance should be given. DRAW OFF SUMP Adrawoffsumpisprovidedatthebottomofthetanksuchthatashells inclination is given to the bottom plates towards the sump. Sump shall be placed in foundation before bottom placement. A neat excavation shall be made to conform totheshapeofthedrawoffsump.Thesumpshallbeputinplace,andthe foundationshallbecompactedaroundthesumpafterplacementandthesump shallbeweldedtothebottom.Drawoffsumpisprovidedinordertocollectthe 17 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. waterparticlesintheoil.Adrawoffnozzleisprovidedontheshellplateto removethewatercollectedinthedrawoffsump.Thesumpandnozzleare connected by means of an internal pipe. SHELL Shellisthemajorportionofthetankwhichisexposedtotheatmosphere.The majorproblemthatmayariseiscorrosion.Shellplatesgenerallygetcorroded internallywhere liquid-vapor ismaintained. Internal corrosion in the vapor space is notcommonly caused by hydrogen sulphide vapor, water vapor-oxygen giving pitting type corrosion. Atmospheric corrosion can occur on all external parts of the tank.Thistypeofcorrosionmayrangefromnegligibletoseveredependingon upon the atmospheric condition of the locality.SHELL OPENINGS The important shell openings are shell man hole, yield and suction nozzles, water drain and rain drain. 1.SHELL MANHOLE Onemanholeisprovidedtothetankshellatthebottomshellcourseforthe entry of humans into the tank for maintenance or other purposes. 2.YIELD & SUCTION NOZZLES Threeyieldnozzlesandonesuctionnozzleareprovidedforthetank.These nozzlesarealsofixedatthebottomshellcourse.Yieldnozzleisprovidedfro receivingfinished,intermediateorunfinishedproductsintothetank.Thisnozzle is designed according to the velocity of yielding and need for agitation.3.WATER DRAIN AND ROOF DRAIN Nozzles for water draw off and roof drain are provided in storage tanks. The water drains are fixed at 120 degree apart on the bottom shell course. 18 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. WIND GIRDER Windgirderorstiffeningringsareprovidedonstoragetankstopreventthe bucklingoftanksagainstwindloads.Windgirdersareusuallyconstructedas walkways to facilitate the inspection and repair of storage tanks. FLOATING ROOF Floatingroofareinstalledinoilstoragetanksprimarilytoreduceevaporation& handlinglosses,todecreasecorrosionandtoreducefirehazards.Floatingroofs may be of pan type, single deck pontoon type or double deck pontoon type. WHY USE FLOATING ROOF? 1.Floating roof tank reduces breathing loss Whenavolatileproductisstoredinafreelyventilatedfixedrooftankthe concentrationofvolatilevapourinthevapourspacewillvarydependingonthe tankoperationconditions.Duringholdingperiods,whennoliquidisaddedor removedthevapourspacewillcometotheequilibriumbasedonproduct temperatureandvapourpressure.Emissionsduringholdingaregeneratedbythe vapourspacebreathingprocess.Asaresultofdailyambientheatingandcooling processes,theair-vapourmixtureinthevapourspaceexpandsandcontracts. During the daily heating process, some of the air vapour mixture is expelled from the tank, resulting in the evaporative emissions. During the product cooling air is drawnintotheproductspacethathelpstodilutetheconcentration.Thisinitiates further evaporation that continues until the space again reaches equilibrium. 2.Floating roof reduces filling loss Normal tank filling and send out operations also affect the vapour space of a fixed-roof tank when product is removed from the tank air is drawn to the vapour space. Unless the tank is completely emptied, the air in the new, larger vapour space will become saturated with product vapour. During the holding period before the next tankfillingoperation,evaporativebreathinglosseswillincreaseduetothe 19 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. increasedvolumeofthevapourspace.Whenproductisaddedtotankthe increasingliquidvolumedisplacestheair-vapourmixturethroughthetankvent, resultinginsignificantevaporativeemissionsthananyothertankoperationina fixed-roof tank. 3.Safety Crudeandrefinedpetroleumproductsarevolatileinnatureandwillreadily evaporativeatnormalstorageandhandlingconditionsproducingvapourthatare combustibleoverarangeofconcentrationswithair.Ithasbeenshownthatthe additionofaweldedfloatingrooftoanopenrooftankcanproducethe evaporativeemissionsbymorethan98%.Properlydesigned,thefloatingroof, floatingroofsealsandfloatingroofdeckfittingscancontrolthequantityand releaseofproductemissionstotheenvironment.Topreventtherooffrom bottomingandfailingaccesspipesetclocatedinthetankbottomandalsoto [provideunderroofaccessforcleaningandinspection,verticallegsupportsare provided for holding the roof about I or 2m above the bottom. ToenablethefreemovementoftheroofupanddownintheshellIthenormal floating condition, a flexible seal is installed between the roof and the shell. The buoyancy of the roof is supplied by the pontoons which cover approximately 25% of the total area. The codes stipulate that the minimum pontoon volume shall besufficienttokeep.Therooffloatingontheliquidwithspecificgravitynot exceeding 0.7. if the single deck and two pontoon compartments are punctured and the primary roof drain in considered inoperative.ROOF LEGS Topreventdamagetothefittingslocatedbeneaththefloutingroof, clearancefor tankcleaningandrepair,rooflegsareprovidedtoholdtheflatlingroofata predetermineddistanceabovethetankbottomwhenthetankisemptied.The larger the diameter of the tank, the greater the number of legs required. Roof legs generally consist an adjustable pipe leg that passes through a slight larger diameter verticalpipesleeve.Thesleeveisweldedtothefloatingroof,extendingboth 20 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. aboveandbelowit.Steelpinspassedthroughtheholesinthesleeveandlegto permit height adjustment. ROOF OPENINGS Various roof openings generally [provided are 1.Deck manhole 2.pontoon manhole 3.roof drain opening 4.opening for bleeder vent 5.opening for gauging Deck Manhole A manhole is provided on the deck which facilities the inspection and checking by allowing the worker inside the tank. 21 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Pontoon Manhole Amanholeisprovidedoneachcompartmentofthepontoonforcheckingand inspection. It also facilitates the repair work of the pontoon. Opening for Gauging Anopeningofabout15inchdia.ismadeonthepontoonsfortheinstallmentof gauge pipes. ROOF DRAIN Roof drains are made such that minimum size drain shall be capable of preventing roof from accumulating a water level greater than design at the maximum rain fall rate,whentheroofisfloatingatminimumoperatinglegal.Roofdrainshallbe made of flexible hose or may be joined type. A check valve shall be provided near theroofendonthedrainpipetopreventbackflowstoredproductifleakage occurs. In joined type the drain pipes are connected using swivel joints.22 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. SEAL The space between the outer rim of roof and shell should be sealed by an approved sealing device and sealing material should be resistant top the stored product and durableagainstfrictionduetoroofofmovement.Sealingsystemshouldexert sufficientsealingpressureinalldirectionstopreventanyevaporationlossesand the arrangement should touch the product during the operation. 23 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Foamsealshaveexcellentflexibilityandrecoveryfromcompressionandatthe sametimepermittheroofmovementupanddownfreelywiththeleveloftank contents. AUTOMATIC TANK GAUGING AutomaticTankGauging(ATG)iscarriedtoobtaininformationaboutthetotal volumeorweightoftheproductinthetank.Thisinformationisobtainedfrom four parameter ie, liquid level, tank capacity tale, average temperature and relative density of individual tank. ADVANTAGES OF TANK GAUGING 1.Accurate and better inventory control 2.reduction of work load 3.tank level is displayed at the tank site and at the central monitoring unit for prompt attention 4.Accurate level measurements even under turbulent product condition COOLING SYSTEM Storagetanksareequippedwithwatercookingsystemtobringdownthe temperatureofthetankshell&protectthemfromdamagewhenafirehazard occurstoaneighboringtank.Thesystemconsistsofringsfittedthroughwhich water is sprayed to the tank shell at a particular pressure.FOAM SYSTEM Foam for fire fightingpurposes is an aggregate of air filled bubbles formed from aqueous solutions and is higher in density than the lightest flammable liquid. It is principally used to form a coherent floating blanket on flammable and combustible liquidslighterthanwaterandpreventsorextinguishesfirebyexcludingairand cooling the fuel.The foam generally used in modern tanks is AFFF (Aqueous Film FormingFoam).Itisasyntheticfilmformingconcentrateandisbasedon fluorinatedsurfactantsplusfoamstabilizersandisdilutedwithwatertoa3%to 24 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. 6%solution.ThefoamformedactsasabarriertoexcludeairorO2andto develop an aqueous film on the fuel surfacecapable of suppressing theevolution offuelvapour.ThefoamproducedwithAFFFconcentrateisdrychemically compatible and thus is suitable for combined use with dry chemicals. MATERIAL SPECIFICATIONS FOR STORAGE TANKS The materials used in the construction of storage vessels are usually metals, alloys, clad-metals,ormaterialswithliningsthataresuitableforcontainingthefluid. Wherenoappreciablecorrosionproblemexiststhecheapestandmosteasily fabricatedconstructionmaterialsisusuallyhotrolledmild(lowcarbon)steel plate. Lowcarbonsteelsarerathersoftandductileandareeasilyrolledand formedintothevariousshapesusedinfabricationvessels.Thesesteelsarealso easilyweldedtogivejointsofuniformstrengthrelativelyfreefromlocalized stresses.Theultimatetensilestrengthisusuallybetween380Mpaand450Mpa and the carbon content between 0.15% and 0.25%. ThematerialgenerallyusedformanufacturingstoragetanksinIndiaisIS2062 grade A. it is low carbon, hot rolled steel with the following specifications. Carbon (max)0.23% Manganese (max)1.50% Sulphur (max)0.050% Phosphorous (max)0.050% Silicon (max)0.40% It has a minimum ultimate tensile strength of 410.6 Mpa and anyield strength of 247.6Mpa.The pipe material used for making roof legs is AI 06 grade B. the chen composition is given below: 25 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Carbon (max)0.03% Manganese (max)1.06% Sulphur (max)0.048% Phosphorous (max)0.058% Silicon (max)0.1% Theminimumtensilestrengthis414Mpaandtheminimumyieldstrengthis241 Mpa. PROCEDURE Assume the values of Height of tank (H) and the diameter of tank (D) Divide the height into number of courses Find out the maximum allowable design stress and the maximum allowable hydrostatic stress for each course Also find out the volume of shell course Then find out the total volume of the shell Find out the total cost of shell plate in that case Repeat the procedure in 2 or 3 cases Design the wind girder based on API standards Location of wind girders based on API standards Data of shell openings based on API standards Data of man hole based on API standards Data of Bolts based on API standards Data of floating roof based on API standards Data of Pontoon based on API standards Data of Rolling ladders and spiral stairways based on API standards 26 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. FOUNDATION BITUMEN CARPETING Sieved river sand is mixed with 8-10 % by volume of bitumen (80/100grade) and islaidonthesiteandconsolidation,rolling,tampingetcaredone.Aslopeof 1:100 is maintained towards the shell from the core of the tank. LAYING OF SHELL COURSE Thelayingofshellcoursefromtoptobottom.Thetopmostshellcourseislaid first. Then the whole course is lifted with the aid of hydraulic jack. The next shell course is laid and so on. In case of a roof type tank, the roof may be erected on top mostshellcourseinthebeginningaslaterinstallingofroofatsuchgreatheight maybedifficult.Themetalplatesusedformakingtheshellcourseneedtobe rolleddependingontherequiredcurvature.Weldingisperformedtojointhe rolledplates.Verticalweldingisperformedtojoinmetalinasamecourseand horizontaltojoinadjacentshellcourses.Theweldingprocedureandmethods performed are mentioned as below: DESIGN AND CONSTRUCTION OF STORAGE TANKS ThedesignandconstructionoftanksisbasedonAPI650(11th edition2007) standards Deign and construction of storage tank number 350 for storing High speed diesel (HSD). Tank SelectionHigh speed diesel (HSD) highly volatile product. Its flash point is of 23 65o C. So it comes under class B of petroleum products and has to be stored in an internal floating roof tank. Height and diameter27 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. For fixing the height and diameter of the tank, the criterion to be maintained as per API 650 is that ratio of the total height of the tank to the internal diameter must be less than 1.5 Height of tank (H) Diameter of tank (D) Height and diameter mostly depends upon the space available on the site, distance betweentwoconsecutivetanksetc.italsodependsonthejudgmentofthe designer. By studying the H/D ratio of the existing tanks in BPCL. Design Capacity of the tank Diameter of the tank = 36.58m Height of the tank= 14.2m Volume of tank=

=

=

=14915.76057 14000 KL Here, H/D ratio= 14.2/36.58 = 0.38< 1.5 SoitispossibleaccordingtoAPI650.(Alsotheeconomicconditionis maintained).BOTTOM PREPARATIONCone penetration test Toassessthesoilbearingcapacityofsoilatlocationsunderthebottomplate penetration test was conducted by IIT Madras. Cone penetration resistance (CPR) wascalculatedbydeterminingthenumberofblowsrequiredtoattaina300mm penetration by a test cone. 1658 So design is feasible [as per API 650 requirements, calculated value of section modulus (Zxx) should be greater than required section modulus (Z)] Location of Primary Wind Girder The primary wind girder is provided as a walk way at a distance 1067 mm fromthetop.Herethereisnochangeindesignandlocationofprimarywind girder, because of there is no maintenance work. So we take the existing data from the previous design data according to API 650 11th edition 2007. Design calculation of secondary Wind girder Requirement of Second wind Girder Maximum height of the un stiffened shell = H1 = 9.47 x t (r/D)3* 190 2 V (According to API 650, cl5.9.7.1) t = Thickness of top shell course = 5mm 50 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. D = Nominal tank diameter = 36.58m H = 9.47 *5*(5/36.58)3* (

2 H= 3.370 m Transformed shell As per API codes the transformed shell shall be calculated as the change in actual width of each shell course into a transformed width of each shell course having a top shell thickness by the equation.Wtr = W{(t uniform / t actual)5} [API 650 cl 5.9.7.3] Where; Wtr= transformed shell course in mm W = Actual width of each shell course in mm tuniform=Thicknessoftopshellcourseinmmexcludingthecorrosion allowance. tuniform = 5 mm tactual = Ordered shell course thickness excluding the corrosion allowance in mm for which Wtr is being calculate. First,second and third courses Tactual = 8mm - 3mm C.A=5mm W=5640mm So Wtr=5640*[(5/5)5]0.5 = 5640mm Fourth course tactual=10mm - 3mm C.A=7mm W=2425mm So Wtr=2425*[(5/7)5]0.5=1045.7mm Fifth course 51 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Tactual=12mm - 3mm C.A=9mm W=2125mm So Wtr=2125*[(5/9)5]0.5 =488.8mm Sixth course Tactual=14mm - 3mm C.A=11mm W=2000mm So Wtr=2000*[(5/11)5]0.5 =278.59mm Seventh course Tactual=16mm - 3mm C.A=13mm W=2000mm SoWtr=2000*[(5/13)5]0.5 =183.48mm Transformed width wtr =5640+1045.7+488.8+278.59+183.48 = 7636.57mm According to API 650 (11th edition 2007, [3.9.7.3]), if height of transformed shell isgreaterthanmaximumunstiffenedheight,H1.anintermediatewindgirderis required. No: of secondary wind girders required =height of transformed shell Maximum un stiffened height = 7636.57/3370 = 2.26> 1 Since ratio is greater than one, one number of secondary wind girders is required. Location of intermediate wind girder As per clause No.5.9.7.3, 5.9.7.3.1, &5.9.7.3.4 the secondary wind girder shall beprovided,thegirdershouldbelocatedatthemiddleoftransformed shell(7636.57/2=3818mm),Theexistingwindgirderataheightof3320mmfrom primary wind girder. 52 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Thepreviouswindgirderwastoosmallforawalkway(200mm)thereforwe changedthedimensionandconstructedanewsecondarywindgirderofwidth 600mm, which made inspection around the tank possible. V.SHELL OPENINGS 1.MAN HOLE (SHELL) One -man hole provided to the tank shell at the bottom shell course. 0.790m 2.425m 2.425m 2.425m 2.125m 2m 2m 1067mm 3818 mm 53 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. It is enough to provide 600 mm manhole. Minimum thickness of cover plate, tc = 16 mm Thickness of bolting flange tf = 11 mm (API 650 table 3.3) Man hole diameter, Dm = 914.4 mm Cover plate diameter, Dc = 820 mm (API 650 table 3.5 page 5-18) BOLTS Number of bolts= 42 Diameter of bolts= 22 mm Diameter of bolt hole= 24 mm (API 650 3.4 A) e. DRAW OFF SUMP Twodrawoffsumpsisprovidedatthebottomplateinordertostorethewater content in the product and to remove it. (Note: Two is selected according to Tank no: 019KR) Diameter of sump, A= 1220 mm Depth of sump, B= 610 mm Distance from center pipe to shell, C= 150 mm Thickness of plates in sump = 10 mm Minimum internal pipe thickness = 114.3 mm Minimum nozzle neck thickness= 3 mm 54 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. VI.COOLING WATER SYSTEM DATA CoolingwatersystemisprovidedtothetankasperOISDcodes.Thecooling water is sprayed onto the tank with the help of nozzles. INPUT DATA Type of tank: floating roof tank Diameter of the tank: 36.58m Height of the tank: 14.2m Wind girder from bottom: 13.2m Design code: OISD 116 Thecoolingwaterissprayedontothetankwiththehelpofnozzleson three set of pipe rings around the shell as per the new design aspects. Area below primary wind girder (AI)= x36.58x13.2 Total surface area = 1556.16m2 55 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. SinceOISDspecifiesthataminimumof3litershastobesprayedper minute per unit. Area of the shell, the total amount of water required = 1556.16 x 3 = 4668.48 (1p liters per minute) Consideringthepressurelossesinthepipesconnectingtheringandthewater tank,theoperatingpressureofthenozzleiscalculatedtobebetween1.5to 3.5kg/cm2.Twosetsofcoolingwaterringsareprovided,oneabovetheprimary wind girder, and the other below the secondary wind girder. Ring no;1 Surface area to be cooled by the water from top ring = Dh D = dia of the tank= 36.58m H = distance between two wind girders = 6 m Surface area = x 36.58 x 6= 689.16 m2 Water required= 3 x surface area= 3 x 689.16 = 2067.50lpm VII.FOAM SYSTEM PROVIDEDFoam recommended= AFFF Foam application rate= 12 liters/min/m2 of seal area. (As per OISD 116) Foam dam width= 1 m D, diameter of the tank= 36.58m Height of the foam dam= 600mm= 0.6 m 56 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. VII.FLOATING ROOF Theroofandaccessoriesshallbedesignedandconstructedsothattheroofis allowedtothefloattothemaximumdesignedliquidlevelandthenreturntoa liquid level that floats the roof well below the top of the tank shell without damage to any part of roof and accessories. Deck plate data As per the API 650 standards deck plate shall have a minimum thickness of 5 mm (Cl C.3.3.2, pg C-1, API 650) So the thickness of deck plate selected = 5 mm Dimensions= 6300x1500x5thk Total weight=31527.56kgThe deck plate shall be provided with a roof manhole, rain-drains, support legs etc. Pontoon data No.of components(N)= 38+1=39Qty Pontoon bottom plate= 6300x1500x5thk Pontoon material= IS 2062 Gr A Weight of single pontoon= 39.25 kgTotal weight of pontoon=15318.17kg 57 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. 110 1050 1000.571000.571000.57

3.06m Pontoon Deck 36.58 m 3066.69 200 600 600 Pad Deckplate 58 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Data of Rolling ladder and spiral stairways Rolling ladder rolls over a certain path with the help of wheels which are made of steel and having a brass cap to prevent spark. Length of ladder = 17960 mm. Track slope = 1 : 100 Supporting legs The floating roof shall be provided with support legs. The length of support legs shall be adjustable from the top side of the roof. According to API 650 standards the length and attachment shall be designed to support the roof and uniform live load at least 1.2 KPa. 59 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. INSPECTION OF STORAGE TANKS INSPECTION PROCEDURES Beforecommencingtheinspectionofatank,alldetailsgiveninthehistorycard andrecordshallgonethrough.Inspectionoftankisneededtobecarriedoutat differentstagedofitsmaking.Thetankisinspectedforitsroundness,proper curvature, the welding carried out, local deviations. Inspection shall include:Study of all technical specifications and the code to which the tank is to be built.Checking the foundation pad and slope Identification of plate materials Qualification of welding procedure and welding operator Checking of painted underside of the bottom plate prior to these being laid Checking of each batch of electrodes as per specifications and assurance of its use as per suggested methods of their manufactures and codes. Checking of proper weldingsequence Evaluating spot radiology of butt welded annular (radial) joints and vacuum box test of the portion of the weld on the bottom plate in which shell is to be erectedChecking of fits ups and noting of curvature and plumb readings before and after welding of the shell courses 60 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Inspection of Welds Butt-Welds Completepenetrationandcompletefusionarerequiredforjoiningshellplatesto shellplates.Inspectionforqualityofweldsshallbemadeusingeither radiographicmethodsorultrasonicmethod.Visualexaminationmayalsobe done. Fillet-Welds Filletweldsshallbeinspectedbyvisualmethodofexamination.Thefinalweld shall be cleaned to slag and other deposits prior to inspection. Inspection of Tank bottom Uponcompletionofweldingoftankbottom,bottomweldsandplatesshallbe examined visually for any potential defects and leaks. In addition to it can be done by vacuum test tracer gas test. Inspection of Reinforcement plate welds Afterfabricationiscompletedbutbeforethetankisfilledwithtestwater,the reinforcementplatesshallbetestedbyapplyingupto100kPagaugepneumatic pressure between the tank shell and the reinforcement plate on each opening using the tell-tale hole specified.Testing of shell After entire tank and roof structure is completed, the shell shall be made tested by one of the following methods. (i)If water is available for testing shell, the tank shall be filled with water as follows (ii)To maximum design liquid level, H (iii)Foratankwithatightroof,to50mmabovetheweldconnectingthe roof plate or compression plate to top angle or shell (iv)To a level lower than specified in sub items i) or ii) when restricted by over flows. 61 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. a.If sufficientwater is not available to fill the tank, tank may be tested by paintingallofthejointsoninsidewithahighlypenetratingoiland carefully examining the outside of joint for leakage. b.Applyingvacuumtopeithersideofjointsorapplyingairpressureas specified in roof test. Testing of RoofIt can be done by Applyinginternalairpressurenotexceedingtheweightofroofplatesand applyingtoweldjointsasoapsolutionorothermaterialsuitablefor detection of leak. Vacuum testing of weld joints VISUAL INSPECTIONVisual external inspection of each tank shall be madeonce inayear. During the visual inspection, following shall be checked. Protective Coatings Conditionofpaintshallbecheckedvisuallyforrustspots,mechanicaldamage, blisters and film lifting. Roof Plates Roof plates shall be inspected for defects like pin holes, weld cracks, pitting etc, at water accumulation locations. Ladder, Stairways, Platform and Structures Theseshallbeexaminedforcorrodedorbrokenparts.Freemovementand alignment of wheels on rolling ladder shall be checked. ladder and staircase steps (trends) shall be checked fro wear and corrosion. 62 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Tank Pads Tanks pads shall be visually checked for settlement, sinking, tilting, sapling cracking and general deterioration. Propersealingofopeningbetweentankbottomandtheconcretepadshall bechecked (no water shall flow under the tank bottom). Slope of tank pad shall be checked to ensure water drainage Anchor bolts Anchorboltswhereverprovidedshallbecheckedfortightness,andintegrityby hammertesting.Theseshallalsobecheckedforthinning/bending.Distortionof bolts is an indication of excessive settlement. Concrete foundation atanchor bolt shall be checked for cracks. Fire Fighting System General condition of fire fighting facilities and sprinkler systemsprovided on the tankwithrespecttocloggingofspraynozzles,perforationoffoamconnections, etc,shallbechecked.Frequencyandprocedureforcheckingshallbeoverasper OISD-Std-142 (Inspection of Fire Fighting Equipment). Vents and Pressure Relieving Devices Allopenvents,flamearrestorsandbreathervalvesshallbeexaminedtoensure thatthewiremeshandscreensareneithertornnorcloggedbyforeignmatteror insects. Rim and bleeder vents for floating roof tanks shall be examined for proper working.Allventsandpressurerelievingdevicesshallbeinspectedasperthe frequencyandprocedureoutlinedinOISD-Std-132(InspectionofPressure Relieving Devices). 63 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Insulation Ifatankisinsulated,theinsulationandweatherproofsealingshallbevisually inspected for damage. The water proofsealing of the insulation shall be examined every year, since the entry of moisture will greatly reduce the insulating properties andmayalsoresultinseriousundetectedcorrosionofthetankplatesunderneath the insulation.Grounding Connections Grounding connections shall be visually checked for corrosion at the pointswhere theyenterearthandattheconnectionstothetank.Theresistanceofgrounding connectionsshall be checked annually before monsoon.Leaks Thetankshallbeinspectedfroanyobviousleakageoftheproduct.Valvesand fittings shall be checked for tightness and free operations. EXTERNAL INSPECTION Thedetailedexternalinspectionofthetankshallbecarriedoutasperthe frequency mentioned. Thefollowingshallbeinspected/checkedduringexternalinspection,besidesthe visual inspection. 1.Tank fittings, Accessories and Pipe Connection Allnozzlesshallbevisuallyinspectedforcorrosion/distortion.Thickness measurements shall be taken with ultrasonic thickness meter. On nozzle of size 50 mm NB above, minimum 4 readings should be taken. 2.Tank Shell Thetankshellbevisuallyexaminedforexternalcorrosion,seepage,cracks, bulginganddeviationfromthevertical.Cracksmostlyoccuratthewelded connectionsofnozzlestothetank,inweldedseams,attheweldconnectionsof 64 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. brackets or other attachments to the tank and the filletwelds of the shell to bottom plate. The following minimum requirement for the thickness survey is recommended in all tanks. All the plates of first and second course of the shell should be thicknessOnthefirstcourse,3to4readingsshouldbetakenoneachplate diagonally,thebottom,middle,andtoppositionsoftheplatemustbe covered. Onthesecondcourse,tworeadingsshouldbetakenoneachplate.One readingshallbenearthelowerweldjointandtheotheratapproachable height. 3.Tank Roofs Floating Roofs On a floating roof, during visual inspection, the following shall also be thoroughly checked. Paint condition Depressions Pontoonboxesandbuoysfromleakages,indications/marksofseepage and corrosion Roof and emergency drain Drain shall be checked for breakages and blockages on the check valve fitted on to theroofdraininletend.Emergencydrainsshallbecheckedforwaterleveloil spillage on roof deck.Floating roof seals Beforemakingaregularinspectionoffloatingroofseals,thedrawingsofseals shall be studied so that operation and possible damages are well understood. 65 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Floatingroofsealsshallbevisuallyinspectedeveryyear.Allsealsshallbe inspectedvisuallyforcorroded,erodedorbrokenpartsanddeterioratedsealing materials.Exposedmechanicalpartssuchassprings,hanfers,counter-balance, pantographsandshoesaresusceptibletomechanicaldamage,inadditionto mechanical wear and atmospheric or vapour space corrosion. The rubber seal have fairly close contact with tank shell plates. a.Hinge bolts at the top of ladder and its rollers b.Earthing of the ladder c.Lateral movement, rotation and titling of roof d.Electrical continuity between the floating roof and tank shell. 5.Projectingout portion of bottom plates Theprojectingoutportionofthebottomplates(annularplates)shallbevisually examined for any corrosion/thinking ultrasonically gauged. INTERNALINSPECTION Prior to internal inspection, an externalinspection of the tank shall be done as specified earlier.Beforecommencingtheinternalinspection,thetankmustbeemptiedofliquid, freed of gases and cleaned out.Roof and Structural Members Floating Roof Theundersideandinternaloffloatingroofshallbeinspectedforcorrosionand deterioration.Thefloatingroofsealsshallbeinspectedfromtheunderside.The legsandsleevedoffloatingroofshallbecheckedfordeterioration,bowingand shifting.Thicknesssurveyofthepontoonboxesandcheckshallbecarriedout. Any suspected pontoon/buoy compartment shall be checked with air and suds. II.Tank Shell Entire tank shell shall be visually scanned for signs of corrosion, pitting, cracking etc. Finding of external inspection, service condition and history shall be guiding 66 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. factorsforsuchobservations.Allweldjointsshallbeexaminedcarefully.The vapourspaceandliquidlevellinearelikelyareasofcorrosion.However,ifthe wallsarealternatelywetanddryortheconceptsarecorrosivechemicals,the entire can be attacked.III.Tank Bottom After the tank has cleaned of its sludge, it shall be visually inspected to obtain the firstindicationoftheconditionofthebottom.Thetankbottomplatesshallbe visually inspected for pitting, corrosion and weld cracks. The weld joints shall be thoroughlycleanedandvisuallyinspectedforcracksordefectsbymagnifying glasswhereverjointsofshellandannularringandinspectedforanyleakage. Depressions in the bottom and in the areas around or under the roof supports and pipecoilsupportsshallbecheckedclosely.Corrosionontheundersideofflat bottomtanksrestingonsoiloronpadscannotbecheckedfromoutside.From ultrasonicthicknessinstrumentarealsoindicationsofundersidecorrosion.To carryoutapositiveinspectionandaccuratecheck,itisrecommendedtocutout representativesectionsofcoupons(atleast30mminleastdimension)ofbottom plate.IV.Water draw-offWaterdrawoffsubjectedtointernalandexternalcorrosionaswellascracking. Theyshallbevisuallyinspectedandhammertestedalongwiththicknesssurvey as feasible. Bottom plate under dip hatch shall be checked for dents, etc. Drainsumpsshallbecarefullycheckedforcrack,pitting,leakintheweld,and measuredinparticularwhencorrosionattheundersideofthetankbottomplates has been suspected. V.Linings When the inside surface of a tank are lined with corrosion resistant material such as sheet lead, rubber,organic and inorganiccoatings, or concrete inspection shall bemadetoensurethattheliningisingoodcondition,thatisinproperpositionand it does not have holes or cracks in the rubber lining as evidenced by bulging. 67 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Hardness testing of the rubber lining shall be carried out while inspecting the tank internally. VI.Roof drains Roofdrainsonthefloatingroofcanbedesignedinmanyways.Theycanbe simpleopendrainpipes,swiveljointsorflexiblehosedrainsthatkeepthewater fromcontaminatingthecontents.Properfunctioningoftheroofdrainsshallbe ensured otherwise this may lead to sinking or over turning of the floating roof.TESTING METHODS1.Dye-penetrating testing It is used for detecting discontinuities open to the surface Basic process 1.Surface penetration and pre cleaning 2.Applying a visible or fluorescent liquid penetrant to surface 3.Wait for the penetrant to enter surface breaking discontinuities 4.Removing excess penetrant from the surface 5. Applying a developer to the examination surface 6.Interpretation of indication 7.Dye penetrant testing Advantages i.Easy to apply and cheap ii.Interpretation easier iii.Can be used for any metal Disadvantages i.Can detect only surface discontinuities 68 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. 2.Magnetic Particle Testing Used to detect surface and sub surface discontinuities Basic process 1.Magnetic field is induced in the specimen 2.The discontinuities lying in a direction transverse to the field will cause a leakage flux to develop around it. 3.Fine magnetic powder if sprinkled on this will adhere to in the vicinity of leakage flux. 4.Magnetizing yoke 5.Florescent iron powder 6.Black light source 7.BothACandDCcurrentcanbeusedforproducingmagneticfield permanent magnets are also used for the same Advantages i.Can be used for surface and sub surface discontinuities up to 5mm ii.Interpretation easy Disadvantages i.Can be used for only ferrous metals ii.Residual magnetism is a problem iii.Power requirement 3.Ultra sonic Testing Ultrasonicwavesaresoundwaveswithfrequencyabovetheaudiblerangeie, above 20000 Hz. This method is used to detect all types of defects ie, volumetric NDT. 69 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Basic process1.Ultrasonic waves propagated through the material 2.Anychangeofmediumreflectsthewavesduetochangeinacoustic impedance 3.Defects of material are change of acoustic impudence 4.The reflected waves are detected using cathode ray tubes 5.The amplitudeand distance in the CRT will give an indication on the type and position of the defect 4.Radiographic test (Applicable only at shell, annular plate joints)Used to detect all kinds of defects Basic process ItisavolumetricexaminationusingX-rayradiationornuclearradiation that penetrates through the specimen and produces an image on the film. Radiation is absorbed as it passes through the material Theabsorptiondependsontheamount,densityandatomicno.ofthe materialA discontinuity causes a condition of less material of lesser density. Theimagedependsontheamountontheamountoftransmittedraysthat strike the film Radiographic source can be either X-raytubes or Gamma radiation source X-ray gives better quality of image GammaraysourcescontainradioactiveisotopesofIridium192orCobalt 60 Advantages Any kind of defects can be detectedGives a permanent record Defect location and positioning is more accurate 70 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. Disadvantages Radiationsafetyisanareaofconcernespeciallyincaseofgammaray sources Theoperatorsarelikelytobeexposedtoradioactiveradiationandneeds constant monitoring The test results will take some time- processing time of film . 71 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. CONCLUSION Introducingafloatingtyperoofforthestoragewouldmeanincreased safetylevel.ThegivenparametersweretodesignandstoreHSDinatankof diameter 36.58 m to height of 14.2m of plate of IS-2062A was used. The tank was designedtostore14000KI.Thedesigningwasdoneaccordingtothefulldesign specification as required by the industry using American Petroleum Institute (API 650-11th edition, 2007) design data. After the designing was completed the design was checked with the existing parameters. The inspection of tank was also studied at different stages of its construction. 72 Design & Maintenance of storage tank for HSD AWH Engg. College CalicutDept. of Mechanical Engg. REFFERENCES 1.AMERICAN PETROLEUM INSTITUTE (API) 650, 11TH EDITION, 2007. 2.OIL INDUSTRIES SAFETY DIRECTORATE (OISD)116. 3.Text Book of Introduction to Storage Tank . 4.Guide to Storage Tank and Equipments 5.API 653 2009 (Only for repair)