7/30/2015 FullyrefrigeratedtankersthatcarryLPG,Ammonia&Vinylchloridehttp://www.liquefiedgascarrier.com/FullyRefrigeratedShips.html 1/6Homepage|||LNGhandling|||LPGhandling|||OtherGasproducts|||Fire&Safety|||Emergencyresponse|||FullyrefrigeratedtankersthatcarryLPG,Ammonia&VinylchlorideFullyrefrigeratedtankersarebuilttocarryliquefiedgasesatlowtemperatureandatmosphericpressurebetweenterminalsequippedwithfullyrefrigeratedstoragetanks.Thetankershaveprismaticshapedcargotanksfabricatedfrom3.5%nickelsteel,allowingthecarriageofcargoesattemperaturesaslowas48C,marginallybelowtheboilingpointofpurepropane.Prismatictanksenabledtheshipscargocarryingcapacitytobemaximized,thusmakingfullyrefrigeratedshipshighlysuitableforcarryinglargevolumesofcargosuchasLPG,ammoniaandvinylchlorideoverlongdistances.TheeconomicadvantagesoftransportingLPGandammoniainafullyrefrigerated,nonpressurisedconditionaremoreevidentforlongerhaulandlargerquantitycargoes.Theselfsupportingprismaticshapeofthecargotanksallowsforabetterutilisationoftheavailableholdspacethanthetypeofshipsdescribedpreviously.Thetanksareusuallydesignedforamaximumworkingpressureofabout0.28kg/cm2(280milibars)andaminimumworkingtemperatureof50oCmakingthemsuitableforthecarriageofbutane,butadiene,VCM,ammonia,propaneandpropylene.WhyHarmonicsSolutions?SaveyourvariablespeeddriveswithMIRUS'harmonicssolution!MirusInternationalInc7/30/2015 FullyrefrigeratedtankersthatcarryLPG,Ammonia&Vinylchloridehttp://www.liquefiedgascarrier.com/FullyRefrigeratedShips.html 2/6Fig:FullyrefrigeratedLPGcarrieratseaCargocapacityTheshipsaretypicallyintherange15,000m385,000m3,withthreecommonsizesforLPG/Ammoniatradesof30,000m3,52,000m3and80,000m3.TemperaturecontrolThetrendforlongervoyageshasimposedademandlargerships,andwiththeincreasingsizeoftheship,thepumpingandrefrigerationplantcapacityhasincreasedproportionally.ConstructionThetanksnearlyextendtothefullwidthoftheship,withballastinthedoublebottomandupperhopperorwingtanks.Thesetanksnormallyhaveacentrelinebulkheadfittedwithtwoequalizingvalves.Youshouldbecautiousshouldthesevesselsdevelopalistalongsideasthetankscarryalargefreesurfaceareaandifthevesselhasproblemswiththeballastorlevellingthecargoduringloadtheycanquicklylistoverto2or3.Type'A'tanksType'A'tanksareconstructedprimarilyofflatsurfaces.Themaximumallowabletankdesignpressureinthevapourspaceforthistypeofsystemis0.7bargthismeanscargoesmustbecarriedinafullyrefrigeratedconditionatornearatmosphericpressure(normallybelow0.25barg).FigureshowsasectionthroughthistypeoftankasfoundonafullyrefrigeratedLPGcarrier.Thisisaselfsupportingprismatictankwhichrequiresconventionalinternalstiffening.Thetankissurroundedbyaskinoffoaminsulation.Whereperliteinsulationisused,itwouldbefoundfillingthewholeoftheholdspace.7/30/2015 FullyrefrigeratedtankersthatcarryLPG,Ammonia&Vinylchloridehttp://www.liquefiedgascarrier.com/FullyRefrigeratedShips.html 3/6ThematerialusedforType'A'tanksisnotcrackpropagationresistant.Therefore,inordertoensuresafety,intheunlikelyeventofcargotankleakage,asecondarycontainmentsystemisrequired.ThissecondarycontainmentsystemisknownasasecondarybarrierandisafeatureofalltankerswithType'A'tankscapableofcarryingcargoesbelow10C.ForafullyrefrigeratedLPGcarrier(whichwillnotcarrycargoesbelow55C)thesecondarybarriermustbeacompletebarriercapableofcontainingthewholetankvolumeatadefinedangleofheelandmayformpartofthetanker'shull,asshowninthefigure.Ingeneral,itisthisdesignapproachwhichisadopted.Bythismeansappropriatepartsofthetanker'shullareconstructedofspecialsteelcapableofwithstandinglowtemperatures.Thealternativeistobuildaseparatesecondarybarrieraroundeachcargotank.7/30/2015 FullyrefrigeratedtankersthatcarryLPG,Ammonia&Vinylchloridehttp://www.liquefiedgascarrier.com/FullyRefrigeratedShips.html 4/6TheIGCCodestipulatesthatasecondarybarriermustbeabletocontaintankleakageforaperiodof15days.Onsuchtankers,thespacebetweenthecargotank(sometimesreferredtoastheprimarybarrier)andthesecondarybarrierisknownastheholdspace.Whenflammablecargoesarebeingcarried,thesespacesmustbefilledwithinertgastopreventaflammableatmospherebeingcreatedintheeventofprimarybarrierleakage.Fig:FullyrefrigeratedgascarrierunderwayRelatedInformation:1. Thermalinsulationfittedtorefrigeratedcargotanks