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UsingdimensionalcontroltomitigateriskforATPTitan
installation
Published:May1,2010
TomGreaves,SparPointGroup
RobertShivers,ATPOil&GasCorp.
JoseVasquez,RoyCottrell,Bennett&AssociatesLLC
IanMackie,KeithMedley,IntertekHiCad
Theclientisasmallindependentthatjustmadea$600millionbetonanew
deepwaterfloatingplatformtodevelopaGulfofMexicofieldthemajorsconsidered
toosmalltodevelopthemselves.Getitrightandtheclientdoublesproductionnext
year.Getitwrongwell,donotgothere.Mitigatinginstallationriskwith
dimensionalcontrolmakesalotofsensewhenthestakesaresohigh.Hereishow
BluewaterIndustriesdiditforATPOilandGasCorp.(ATP)ontheTitanMinDOC
projectearlierthisyear.
Themomentoftruthforalloffshoreinstallations:Willthetopsidestohull
integrationbe
performed
successfully,
on
the
first
attempt
and
without
interferences?BluewaterIndustriesdeployeddimensionalcontrolservicesfrom
IntertekHiCadatrelevantstagesoffabricationtolimitthepotentialforinstallation
problems,andcostandscheduleimpactsforATP'sMinimumDeepOffshore
(MinDOC3)floatingplatformproject.Installationandintegrationofthetopsides
moduleswascompletedoffshoreinJanuarywithoutincident;nodimensionalfitting
orclashproblemswereencountered.
TheATPTitanproject,adeepwaterdrytreeplatform,isthefirstofitstypetobe
usedintheGoM.ThepatentedMinDOChull,designedbyBennett&Associates
(BASS),consists
of
three
circular
columns
connected
by
triangular
pontoons
and
a
toptensionedriser(TTR)framethatsupportstherisersthroughthecenterofthe
hull.Ontopofthehullsetsatwomodule,"Tshaped"facilitydesignedbyMustang
Engineering.Thestructuremeasuresapproximately726ft(221m)fromthebaseto
thetopofitsderrickandhasadesigncapacityof25Mbbl/dofoiland100MMcf/d
ofgas.TheTitanMinDOChasbeendeployedintheMiragefield(MississippiCanyon
block941),aspartoftheTelemarkHub,andwillbeinitiallyproducingpartofthe
Telemark(AtwaterValleyblock63)andMorgus(MississippiCanyonblock942)fields
viasubseatiebacksinwaterdepthsofapproximately4,000ft(1,219m).Thestakes
arehighdevelopmentoftheTelemarkHubisexpectedtodoubleATP'sproduction
thisyear.
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TitanhullfloatinghorizontallyingravingdockatGulfMarine
Fabricatorspriortosailaway.
Atfirstglance,Titan'sthreecolumnstructureresemblesasemisubmersible,but
motionwise,itsdeepdraftandlowcenterofgravitygiveitpitch,roll,andheave
motionsmoreinlinewithspardesigns.ThisisparticularlyimportantforpostKatrina
designconditions.Thenaturaloscillationperiodsfortheplatformfallwelloutside
thewaveperiodstypicallyexperiencedintheGoM.Furthermore,theMinDOCwas
designedto
be
moved
to
new
locations
over
its
expected
service
life.
The
Titancan
operateindepthsrangingfrom2,000ft(610m)to7,500ft(2,286m)with
comparablepayloadandenvironmentconditions.Moreover,theunitcanbetowed
toanewlocationwiththetopsidesinplace.Assuch,theTitanallowsATPto
considerfieldsthatwouldotherwisebecommerciallymarginalwithconventional
completions.
The18,000ton(16,329metricton),485ft(148m)longhullwasconstructed
horizontallybyGulfMarineFabricatorsatthecompany'spurposebuiltgravingdock
inIngleside,Texas.Duringconstruction,twoofthethree52ft(16m)diameter
uppercolumns
were
supported
by
saddles
located
directly
on
the
concrete
floor
of
thegravingdock,whilethethirdcolumnwasassembledmorethan100ft(30m)up
intheair.Afterhullfabricationwascompleted,the40ft(12m)deepgravingdock
wasfloodedandTitanwasfloatedandtowedtoitsdeepwaterinstallationsite
whereitwasupendedtoitsoperationalpositionbycontrolled,freefloodingofits
lowerhull.
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ProcessmodulebeingloadedoutatGulfIsland
Fabrication.Photo
by
Jeff
Rushing.
Thetopsidesconsistofa3,600ton(3,266metricton)processmoduleanda2,500
ton(2,268metricton)utilitymodulethatwerefabricatedatGulfIslandFabricators
inHouma,Louisiana.Inplanview,thetopsidesstructureisTshapedwiththe
processmodulespanning150ft(46m)acrosstheportandstarboardcolumns.The
utilitymodulespansfromtheforwardcolumntotheprocessmodule,wherethetwo
areconnectedviaastructuralinterface.Weightconstraintsmadeitimpracticalto
fabricatethetopsidesasoneunit;theliftwouldhaveinducedunacceptable
deflectionsorrequiredanimpossiblylargespreaderbarortwocranebargestolift.
UtilitymoduleatGulfIslandFabricationpriortoloadout.
PhotobyJeffRushing.
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IntertekHiCaddelivereddimensionalcontrolforpreinstallationstructuralinterface
compatibilityandidentificationofpotentialinterferencesbetweenthemodulesand
hull.
BluewatercontractedIntertekHiCadinApril2009toprovidedimensionalcontrol
(DC)services
for
the
Titan.In
addition
to
general
construction
support
for
key
components,IntertekHiCad'sscopeincludeddetailedandhighaccuracyasbuilt
dimensionaldatathatassuredcompatibilitybetweenthetopsidestohulland
moduletomodulestructuralinterfaces.Thiscompatibilityanalysisincludedclash
checkingoftheinterfaceenvelopestoidentifypossiblehardclashesandclose
proximitycomponentsthatcouldcauseproblemsduringmoduleinstallation.Asthe
projectprogressed,BluewaterelectedtoexpandIntertekHiCad'sscopetoinclude
assistancewiththeinstallationofthefour80ton(73metricton)risertensioners
andpreinstallationverificationofthetopsidestohullinterconnectpipingspools
basedonasbuiltmodulelocationsrelativetothehull.
Discoveringclashesandinterferencesduringinstallationisaprojectteam's
schedule andbudgetbustingnightmare.Withdayratesforoffshoreinstallation
operationsoftenexceeding$1millionperday,thereiseveryincentivetoshorten
thedurationrequiredforinstallation.Dimensionalcontrolislowcost,highvalue
insurancetosignificantlyreducethatduration.Althougharrangementscanvary,
dimensionalcontrolcontractstypicallyamounttolessthan0.2%oftotalinstalled
cost."ThecostofIntertekHiCad'sserviceswasinsignificantincomparisontothe
negativescheduleandcostimpactsthatcouldhavebeenencounteredduring
fabrication,installation,oroperations.Theirattentiontodetailandcommitmentto
maintainingour
project
schedule
have
solidified
their
involvement
in
future
projects
ofthismagnitude,"saysGeorgeFriedel,VPofOperationsforBluewaterIndustries.
Ofcourse,safetyalwayscomesfirst.Whenliftingsignificantloads,whetheratseaor
onland,thepriorityistosafelyandefficientlylandtheload.Leavingaloadthat
weighsthousandsoftonshangingonthecrane,foranylengthoftime,while
resolvinginstallationissuesintroducesseriousadditionalrisks,includingthe
potentialforacatastrophicaccident.
Inthecaseofoffshoreinstallations,successininstallingmodules(whosetendencyis
to
flex
in
the
lift
condition)
from
a
barge
onto
a
floating
hull
structure
demands
understandingthepotentialdimensionalissuesthatcanbeencounteredduringthe
approach,engagement,andtouchdownofthemodulestothehull.
"Withmatingtolerancesaslittleas0.5in.orlessonmajorstructuralcomponents
fabricatedinseparatelocationsindifferentstates,youneedtheprecisionand
accuracyofDCtomakesureitallfitstogether.Inmostinstances,youonlygetone
shottoinstallmodulesthesizeoftheTitan's,"saysJeffRushingwithBluewater
Industries."Physicalinfluencesinanoffshoreenvironmentmakeitimpracticalto
haveasecondchance."
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InstallationoftheprocessmodulebyJ.RayMcDermott'sDB50.Photo
byJamieArmstrong.
Thismakesreversingtheprocedure(i.e.,liftingthemodulesbackuptofieldcorrect
forstructuralcompatibilityandinterferenceissues)animpractical,andsometimes
impossible,option.
Dimensionalcontrolworkflow
IntertekHiCadoperationsmanager,KyleMcNeil,ledtheteamthatconductedthe
dimensionalcontrolwork.SteponewastomeetwithBluewaterprojectpersonnel
tounderstandthedesigntolerances,deflection,andmovementissuesspecifictothe
Titaninstallationactivities.McNeilisnostrangertooffshoreworkhe'sbeenwith
IntertekHiCadforthreeyearsandspent26yearswithKBRandMcDermottbefore
that.McNeilviewsdimensionalcontrolasaninvestment:"It'sdowntotheclientand
the
investment
in
managing
potential
risk."
UnderMcNeil'ssupervision,IntertekHiCadsurveypersonnelvisitedthehulland
topsidesfabricationfacilitiesatappropriatetimestoexecutethesurveyworkusinga
proprietarysurveyingprocessesandsupportingsoftware.Theaccuracyanddetailof
thesurveyworkwascriticaltoassessthestructuralinterfacecompatibilityandto
detectandvisualizepossibleclashesthatcouldariseduringinstallation.Aseachpart
oftheasbuiltsurveyworkwascompleted,IntertekHiCadprogressivelycalculated
andfittedthepiecestogethertoobtaina"bestfit"amongallstructures.
Constructionsupport
Atonestageofconstruction,theforwardcolumnoftheTitanwassupported
elasticallybystrandjacksandtrusses100plusft(30m)intheairafterassemblyand
justpriortotheinstallationoftheTTRframewhichwouldtieallthreeoftheupper
columnsoftheTitantogether.BASScalculatedtheamountofdeflectionexpectedas
thestrandjackswerereleasedandthestructurewaspositionedinalocationthat
wouldminimizelockedinstressesonthehull.Aspartofthiscriticalconstruction
activity,IntertekHiCadwasaskedtomonitorthepositionoftheTTRframerelative
tothetargetpositionsprovidedbyBASStoanaccuracyof1/16in.(1.586mm)
duringtheweldout.EndResult?Thestresseswereminimizedaspredicted.
Topsidestohullstructuralinterface
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Toproperlymatewiththemodulelegs,stabbingguidesonthehullweredesignedto
allowadjustmentinthex,y,andzdirectionbeforeweldingthemtothehull.This
adjustmentallowancehadtoaccountforfivefactors:1)theasbuiltgeometryofthe
modulelegs,2)theasbuiltgeometryofthemoduletomodulestructuralinterface,
3)theasbuiltgeometryofthehull,4)theweldingtoleranceofthehull,and5)the
geometrychange
anticipated
as
the
hull
moved
from
the
horizontal,
laterally
supportedconditiontotheuprightandfreefloatingconditionoffshore.IntertekHi
Cadsurveyedtheasbuiltlocationsofboththemodulelegsandmoduletomodule
structuralinterfacestodeterminethe"bestfit"ofthemodulesrelativetothehull.
Withthisinformation,BASSwasabletopinpointtheoptimumlocationsforthe
stabbingguidesonthehullwhichsignificantlyreducedinstallationrisksoffshore.
Oncefittedandinplace,IntertekHiCad'sscopecontinuedwithmonitoringthe
stabbingguidesduringweldoutrelativetotargetpositionsthatwereestablished.
WithIntertekHiCad'sexperienceandtwiceadayreadings,theseoptimum
locationswere
accomplished
despite
the
movement
of
the
target
positions
due
to
expansionandcontractionofthehullduringthesummerheat.
OffshoreDCverification
IntertekHiCadcarriedonwiththeDCservicesbymeasuringpossibledeflections
thatmayhaveresultedfromtransportationandupendingofthehullonceitwas
floatedtotheuprightservicepositionandfullyballasted.Thesurveyreadingsthen
werecalculatedandmodeledinAutoCADtodeterminethepositionofthestructural
interfaces,primarilythestabbingguides.ResultsfromIntertekHiCad'swork
confirmedthat
the
forward
leg
column
had
deflected
out
board
by
close
to
the
predictedoffsetandallelevationsheldtoplanewithin3/16in.(4.75mm).
Loweringoftheprocessmoduleontothehullstabbing
guides.PhotobyIsidroRodriguez.
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Oncethehullandtopsidesweremated,thenextstepwastoconnectthepiping
systemsandinstallthespecificallydesignedrisertensionersystem.WithIntertekHi
Cad'sforesighttopresurveythepositionsofthepipingtieinpointsonboththe
topsidesandhullpriortoinstallation,itwasstraightforwardtocarryouttheminimal
surveyworknecessarytocalculatethegeometryoftheclosingspools,which
includedlengths,
flange
angles,
and
bolt
pattern
orientation,
where
applicable.
The
requireddimensionalinformationforselectedspoolswascompletedandissuedto
pipingpersonnelforfabricationcompletionthegoal:firsttimefit.
Theutilitymodulebeinginstalledatnight.PhotobyColes
Hairston.
Confinedwithinthewellbaystructureoftheutilitymodule,therisertensioners
hungsuspendedinmidairforthetransportationoffshore.Surveyworkhadbegun
manymonthsearlierinpreparationoftheinstallation.IntertekHiCADhadplaced
targetsinstrategicpositionsonthetensionersthatwouldallowtheproper
alignmenttobeachievedasthetensionerswereloweredtotheirfinalresting
positionontheTTRframe.Thisalignmentwascritical,asthetensionerswereonly
abletobeloweredintopositionpriortobeingputintoservice.Considerationofthe
utilitymodulewellbaypositionswasincludedintheIntertekHiCADbestfit
calculationsforlocatingthemoduletothehull.Onceagain,goodsurveypreparation
allowedforefficientandaccuratepositioningofthetensionersduringtheoffshore
installation.
DCtechnology
TotalstationsurveyinstrumentsandaccessoriessupportedbyDIMES(IntertekHi
Cad's3Dcalculationsoftware)andAutoCADsoftwarewereusedasthemaintools
fortheprojectsurveywork.TheDIMESsoftwareiscompatiblewithAutoCAD.
IntertekHiCadsurveyorsareexperiencedwith3DCADmodelingtechniques,
allowingtheassurveyeddatatobemanipulatedinAutoCADforthepurposeof
modelingrelevant
information
and
possible
overlay
against
the
design
model
for
interrogation.Inthisinstance,threeseparatemodelswerepreparedforthetopof
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thehullandtheundersidesoftheprocessandutilitymodules.Basedonthe
calculations,themodulesweremovedintopositiononthehullmodel,thereby
allowinginterrogationofthefullinterfaceenvelope.Workingoffshorewithatotal
stationinstrumentoftenrequiresflexibilityandknowledgeoftheacceptable
parameterstobeabletosetuptheinstrumentindifficultsituationsandmaintain
highaccuracy
in
order
to
achieve
the
required
tolerances.
Howisdimensionalcontroldifferentthaninspection?
Here'swhereexperiencewithdesign,fabrication,andinstallationpaysoff.A
dimensionalcontrolexpertengagedthroughoutfabricationcannotonlyidentify
potentialfabricationdimensionalproblemsandtoleranceaccumulationsbutcan
alsoadviseonpracticalsolutionstocorrectfortheaccumulations.Dimensional
controlinsightintofabricationprocesses,experienceandunderstandingof
installationproceduresaswellasknowledgeaboutthecapabilitiesofindividual
contractorslets
DC
experts
inform
project
teams
about
how
to
make
mid
course
correctionsandadjustmentstoavoidpotentialseriousexpensiveproblemsfrom
occurringatthecriticalstages.McNeilsays"ittakesaclientwithanopenmindto
getfullvaluefortheinvestmentbecauseitisnotbusinessasusual."
Otherlessonslearned
Constructionofsomeoffshorestructuresrequiresthecoordinationofmultiple
fabricationcontractors,eachresponsibleforproducingcomponentstoaspecified
tolerance.Thechallengefortheprojectteamistomanagetheaccumulationofthe
variationsbetween
the
nominal
design
dimensions
and
the
as
fabricated
dimensions.Tighteningthespecificationshascostandscheduleimplicationsandin
mostcasesbecomesimpractical.Duetocostandscheduleconcernsaprojectteam
canbepushedtotakeriskonoutoftolerancedimensions.Dimensionalcontrol
appliedaccuratelyandwithconstructionexperienceandknowledgecanprovidethe
assurancethatcomponentswillfittogetherwhenitreallycounts,thefirsttime.
ends
IntertekMediaenquiries:http://www.intertek.com/news/mediacontacts/
IntertekSalesEnquiries: NorthandSouthAmerica:+17134754022
EAME:+390295383833/AsiaPacific:+81352450648
AboutIntertek(www.intertek.com)
Intertekisaleadingproviderofqualityandsafetysolutionsservingawiderangeof
industriesaroundtheworld.Fromauditingandinspection,totesting,qualityassuranceand
certification,Intertekpeoplearededicatedtoaddingvaluetocustomers'productsand
processes,supportingtheirsuccessintheglobalmarketplace.Intertekhastheexpertise,
resourcesandglobalreachtosupportitscustomersthroughitsnetworkofmorethan1,000
laboratoriesandofficesandover25,000peopleinmorethan100countriesaroundthe
world.
http://www.intertek.com/http://www.intertek.com/