78 |
OilfieldTechnology
February
2014
thedeckof thevessel via rollers laidout inconcentric ringsbeneath
the turntableandmounted to thedeckonhardpointsoragrillage to
distribute the load.
Thereare two typesof carousel storageavailable:
Ì
Ì
Basket carousels intowhich theproducts loaded fromaboveand
storedunder zero tension inhorizontal layers.
Ì
Ì
Reel carouselsontowhichproduct is loaded from the sideand is
storedunder tension in successive radial layers.
IHCMerwedecarouselsuseahydraulic roller suspensionsystem
to reducehighpoint contact loadsbeing transferred into thevessel
from themassof carousel andproduct. Thesehigh loadsarecaused
bymanufacturing tolerancesanddifferences indeckstiffnesswhich,
if left ‘unsmoothed’,would result ina reduced fatigue lifeofboth
thecarousel andvessel. Aspartof thedesignprocess, thecompany
undertakes rigorous fatiguecalculationsbasedon thevessel
accelerationsandwavespectracausing fluctuating inertial loading,
that insomecases, drive thedesign requirementsmuchmoreso than
peakoperational loading.
Compared toa fixed roller support system, theeffectofone
ormoreof the fixed rollersbeing installedhigher than the rest is
included in thedesignmodelby forcingadisplacementon the
highest loaded roller inananalysis thatassumesall rollersare
incontact. This increases the loadingsignificantlyon the roller;
generallybya factorofbetween1.7and2 times. Toavoid these
extremelyhighpeak loadson the fixed roller system, apassive
load‑balancinghydraulic rollerarrangement isgreatlyadvantageous.
The rollerunits throughwhichvertical forcesareprimarily
transmittedcomprisea fabricated roller supportand two roller
wheels. Eachwheel hasasteel treadand is tapered toaccommodate
thecircular runningpathof the roller,minimisinganycrabbingof
the rolleras the turntable rotates. The rollerunits for thecarousel
arearranged intoconcentric rings, alignedwith thehardox running
tracks. The rollerunitsaremounted to thegrillage, alongwith
interconnectinghydraulicpipeworkandhoses.
The rollersarearranged inpairswithinabogeyallowing load
share. Thebogey isplacedwithina framepivotedatoneendand
supportedbyahydrauliccylinderwithastainlesssteel rodat
theotherend. Turntable roller loadsarebalancedandoverload
protection isprovidedby thehydraulicsupport cylinders. Thisallows
the loadingateach roller tobecalculatedwithhighcertainty, thereby
minimising thedepthof grillageandmodification to thevesseldeck,
as thepeak loadsare lowerandevenlysharedwithneighbouring
rollers. Thehydraulicsystem therefore reduces thenumberof rollers
andoverallmass. Thedeterministicnatureof loading the rollersalso
dramatically increases the lifespanof thecarousel from10years to
15 ‑20years.
Access to the rollers isviahatcheswithin the table floor, by
rotating thecarousel to theappropriatepositionand lowering the
roller from thehardox track toallowmaintenanceor removal.
Thehydraulic rollersaresuch thatoperation isstillpossiblewitha
failed rollerunitas thiscanbe isolatedand loweredso that it isoutof
contactwith the running track.Thisalsoallows foreasiermaintenance
and roller removalas local jackingof the table isnot required.
Keyadvantagesof ahydraulic roller systemcompared to fixed
roller system:
Ì
Ì
Increased lifespanof carousel.
Ì
Ì
Continuedoperational functionalitywith failed rollers.
Ì
Ì
Improvedaccess to rollers for easymaintenance.
Ì
Ì
Reducedmassandvertical centreof gravity, relative toa
turntablemounted toa fixed support grillage.
Ì
Ì
Minimisedgrillageandmodifications tovessel deck.
Ì
Ì
Rapid supplyof interface information.
Ì
Ì
Rapiddeployment.
Additional equipment canbeprovided toassist in thespooling
ofproductonandoffof thecarousel. This is in the formof a loader
arm forbasket carouselsanda level‑wind tower for reel carousels.
Loaderarmsarenormallymounted toacentralpost inside thecore
Figure2.
Loaderarmandtower.
Figure3.
SapuraKencana-2000tand500tbelowdeckbasket
carousels.
Figure1.
Boskalis–5000tbasketcarousel.
OT_Advert
