DNV Marine Operations' Rules for Subsea Lift Operations

DNV Marine Operations’ Rulesfor Subsea Lift OperationsSimplified Methods for Prediction of Hydrodynamic ForcesTormod BøeDNV Marine Operations29th November 2011

Content• Brief overview of relevant DNV publications• DNV Rules for Marine Operations, 1996,Pt.2 Ch.5 Lifting – Capacity Checks• Simplified Methods for prediction of Hydrodynamic Forceso in Splash Zone, DNV-RP-H103 Ch.4o in Deepwater, DNV-RP-H103 Ch.5DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 2

Relevant DNV PublicationsLifting- and subsea operations :DNV Rules for Planning and Execution ofMarine Operations – 1996 andDNV-OS-H101 Marine Operations, General - 2011’Specially planned, non-routine operations oflimited durations, at sea. Marine operations arenormally related to temporary phases as e.g.load transfer, transportation and installation.’DNV-OS-E402 OffshoreStandard for Diving SystemsOctober 2010DNV Standard for CertificationNo.2.22 Lifting AppliancesOctober 2011DNV Standard for CertificationNo. 2.7-3 Portable Offshore UnitsMay 2011Specially planned non-routine operationsRoutine operationsDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 3

Relevant DNV Publications - Other• DNV-RP-C205 Environmental Conditionsand Environmental Loads October 2010• DNV-RP-H101 Risk Management inMarine and Subsea Operations, January2003• DNV-RP-H102 Marine Operations duringRemoval of Offshore Installations,April 2004• DNV-RP-H103 Modelling and Analysis ofMarine Operations, April 2011DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 4

Content• Brief overview of relevant DNV publications• DNV Rules for Marine Operations, 1996,Pt.2 Ch.5 Lifting – Capacity Checks• Simplified Methods for prediction of Hydrodynamic Forceso in Splash Zone, DNV-RP-H103 Ch.4o in Deepwater, DNV-RP-H103 Ch.5DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 6

Capacity Checks - DNV 1996 RulesPart 2 Chapter 5• Dynamic loads, lift in air• Crane capacity• Rigging capacity,(slings, shackles, etc.)• Structural steel capacity(lifted object, lifting points,spreader bars, etc.)Dynamic loads for subsea lifts are estimated according to DNV-RP-H103DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 7

Capacity Checks – DAF for Lift in Air• Dynamic loads are accounted for byusing a Dynamic Amplification Factor(DAF).• DAF in air may be caused by e.g.variation in hoisting speeds or motionsof crane vessel and lifted object.• The given table is applicable foroffshore lift in air in minor sea states,typically Hs < 2-2.5m.• DAF must be estimated separately forlifts in air at higher seastates and forsubsea lifts !Table 2.1 Pt.2 Ch.5 Sec.2.2.4.4DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 8

Capacity Checks - Crane CapacityThe dynamic hook load, DHL, isgiven by:DHL = DAF*(W+Wrig) + F(SPL)ref. Pt.2 Ch.5 Sec.2.4.2.1• W is the weight of the structure,including a weight inaccuracy factor• The DHL should be checked againstavailable crane capacity• The crane capacity decrease whenthe lifting radius increase.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 9

Capacity Checks - Sling LoadsThe maximum dynamic sling load, Fsling,can be calculated by:Example :Fsling = DHL∙SKL∙kCoG∙DW / sin φref. Pt.2 Ch.5 Sec.2.4.2.3-6where:• SKL = Skew load factor → extra loadingcaused by equipment and fabrication tolerances.• kCoG = CoG factor → inaccuracies in estimatedposition of centre of gravity.• DW = vertical weight distribution → e.g.DWA = (8/15)∙(7/13) in sling A.• φ = sling angle from the horizontal plane.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 10

Capacity Checks - Slings and ShacklesThe sling capacity ”Minimum breaking load”,MBL, is checked by:FslingMBLγsfslingThe safety factor is minimum sf ≥ 3.0.(Pt.2 Ch.5 Sec.3.1.2)”Safe working load”, SWL, and ” MBL, of theshackle are checked by :a) F sling < SWL∙ DAFand b) F sling < MBL / 3.3Both criteria shall be fulfilled (Pt.2 Ch.5 Sec.3.2.1.2)DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 11

Capacity Checks – Structural SteelLifting points:The load factor f = 1.3, is increased by aconsequence factor, C = 1.3, so that totaldesign faktor, design , becomes:design = c∙ f = 1.3 ∙ 1.3 = 1.7The design load acting on the lift point becomes:Other lifting equipment:A consequence factor of C = 1.3should be applied on lifting yokes,spreader bars, plateshackles, etc.Structural strength of Lifted Object:The following consequence factorsshould be applied :Fdesign = design∙ Fsling = 1.7∙ FslingA lateral load ofminimum 3% of thedesign load shall beincluded. This loadacts in the shacklebow !(ref. Pt.2.Ch.5 Sec.2.4.3.4)Table 4.1Pt.2 Ch.5 Sec.4.1.2DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 12

Capacity Checks – SummaryCheckComputeApplyDAF• Lift in air: VMO Rules Pt.2 Ch.5• Subsea lift: DNV-RP-H103CranecapacityDHL• Weight of lifted objectand lifting equipmentCapacityof liftingequipmentF sling• Skew load, CoG and sling angle• Safety factorsDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 13

Content• Brief overview of relevant DNV publications• DNV Rules for Marine Operations, 1996,Pt.2 Ch.5 Lifting – Capacity Checks• Simplified Methods for prediction of Hydrodynamic Forceso in Splash Zone, DNV-RP-H103 Ch.4o in Deepwater, DNV-RP-H103 Ch.5DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 14

Simplified Method, Splash Zone - DNV-RP-H103• The Recommended Practice; ”DNV-RP-H103 Modelling and Analysis of MarineOperations” was issued april 2009. Latestrevision is april 2011.• A Simplified Method for calculatinghydrodynamic forces on objects liftedthrough wave zone is included in chapter 4.• This Simplified Method supersedes thecalculation guidelines in DNV Rules forMarine Operations, 1996, Pt.2 Ch.6.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 15

Simplified Method, Splash Zone - AssumptionsThe Simplified Method is based upon thefollowing main assumptions:• the horizontal extent of the lifted object issmall compared to the wave length• the vertical motion of the object is equal thevertical crane tip motion• vertical motion of object and water dominates→ other motions can be disregardedThe intention of the Simplified Method is togive simple conservative estimates of theforces acting on the object.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 16

New Simplified Method - AssumptionsTime-domain analysis:• Coupled multi-bodysystems with individualforces and motions.• Wind, wave and currentforces.• Geometry modelled.• Motions for all degreesof freedom computed.• Non-linearities included.• Coupling effects.• Continous loweringsimulations.• Varying added mass.• Statistical analysis ofresponses.• Visualization of lift.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 17

Simplified Method, Splash Zone - Crane Tip Motions• The Simplified Method is unapplicable if the crane tiposcillation period or the wave period is close to theresonance period, Tn , of the hoisting systemMKAT33n 2• Heave, pitch and roll RAOs forthe vessel should be combinedwith crane tip position to findthe vertical motion of the crane tip• If operation reference period iswithin 30 minutes, the mostprobable largest responses maybe taken as 1.80 times thesignificant responses• Unless the vessel heading isfixed, vessel response should beanalysed for wave directions atleast ±15° off the applied vesselheadingDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 18

Simplified Method, Splash Zone - Wave PeriodsThere are two alternative approaches:Alt-1) Wave periods are included:Analyses should cover the following zerocrossingwave period range:H s8.9 Tzg13A lower limit of Hmax=1.8·Hs=λ/7 withwavelength λ=g·T z 2 /2π is here used.Alt-2) Wave periods are disregarded:Operation procedures should in this case reflect that the calculations are only valid forwaves longer than:Tz 10. 6 HgSA lower limit of Hmax=1.8·Hs=λ/10 with wavelengthλ=g·T z 2 /2π is here used.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 19

Simplified Method, Splash Zone - Wave KinematicsAlt-1) Wave periods are included:The wave amplitude, wave particlevelocity and acceleration can be taken as:• aH Sv• wa• w 0. 9 aa 2eT z 2 T z 2e42dT2zTg42d2zg• d : distance from water plane to CoG ofsubmerged part of objectAlt-2) Wave periods are disregarded:The wave particle velocity and acceleration canbe taken as:v• wa• w0.30 g Hs0.10g ee0.35dHs0.35dHsDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 20

Simplified Method, Splash Zone - Hydrodynamic ForcesSlamming impact forceSlamming forces are short-term impulseforces that acts when the structure hits thewater surface.A S is the relevant slamming area on theexposed structure part. Cs is slamming coeff.The slamming velocity, v s , is :vsvcv2ctv2w• vc = lowering speed• vct = vertical crane tip velocity• vw = vertical water particle velocityat water surfaceVarying buoyancy forceVarying buoyancy, Fρ , is the change inbuoyancy due to the water surfaceF V gelevation.δV is the change in volume of displacedwater from still water surface to wave crestor wave trough.FV V g~A w2a2ct• ζa = wave amplitude• ηct = crane tip motion amplitude• Ãw = mean water line area in thewave surface zoneDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 21

Simplified Method, Splash Zone - Hydrodynamic ForcesDrag forceDrag forces are flow resistance on submergedpart of the structure. The drag forces arerelated to relative velocity between object andwater particles.The drag coefficient, CD, in oscillatory flow forcomplex subsea structures may typically beCD ≥ 2.5.Relative velocity are found by :Mass force“Mass force” is here a combination of inertiaforce, Froude-Kriloff force and diffractionforce.Crane tip acceleration and water particleacceleration are assumed statisticallyindependent.Fvrvcv2ctv2w• vc = lowering/hoisting speed• vct = vertical crane tip velocity• vw = vertical water particle velocityat water depth , d• Ap = horizontal projected areaM2M A a V A a 233 ct33 w• M = mass of object in air• A33 = heave added mass of object• act = vertical crane tip acceleration• V = volume of displaced water relative tothe still water level• aw = vertical water particle accelerationat water depth, dDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 22

Simplified Method, Splash Zone - BasicsProperties:• Mass, M [kg]• Volume, V [m 3 ]• Added mass, A 33 [kg]Forces:• Weight [N]• Buoyancy [N]Weight = M*g moonBuoyancy = ρ*V*gWeight = M*gDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 23

Simplified Method, Splash Zone - Added MassHydrodynamic added mass for flat platesExample:Flat plate wherelength, b, abovebreadth, a, isb/a = 2.0 : 2A33 0.76 a b4DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 24

A33/A33oSimplified Method, Splash Zone - Added MassAdded Mass Increase due to Body HeightAdded Mass Increase due to Body HeightThe following simplified approximation of theadded mass in heave for a three-dimensionalbody with vertical sides may be applied :2 1A 33 1 A2 33o2(1 ) and h ApAp1.81.71.61.51.41.31.21.111+SQRT((1-lambda^2)/(2*(1+lambda^2)))0 0.5 1 1.5 2 2.5ln [ 1+ (h/sqrt(A)) ]where• A33o = added mass for a flat plate with ashape equal to the horizontal projectedarea of the object• h = height of the object• Ap = horizontal projected area of the objectDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 25

Simplified Method, Splash Zone - Added MassAdded Mass from Partly Enclosed VolumeA volume of water partlyenlosed within large platedsurfaces will also contributeto the added mass, e.g.:• The volume of waterinside suction anchorsor foundation buckets.• The volume of waterbetween large platedmudmat surfaces androof structures.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 26

Added Mass Reduction FactorSimplified Method, Splash Zone - Added MassAdded Mass Reduction due to PerforationRecommended reduction:AAAA33 33S3333SAA3333S1.0 0.7 0.3cos (p 5 ) / e10p28if p< 534if 5 < p < 34if 34 < p < 50A 33S = added mass for a nonperforatedstructure.10.90.80.70.60.50.40.30.20.10Effect of perforation on added mass.e^-P/28BucketKC0.1-H4D-NiMoBucketKC0.6-H4D-NiMoBucketKC1.2-H4D-NiMoBucketKC0.5-H0.5D-NiMoBucketKC1.5-H0.5D-NiMoBucketKC2.5-H0.5D-NiMoBucketKC3.5-H0.5D-NiMoPLET-KC1-4Roof-A0.5-2.5+Hatch20-KCp0.5-1.8Hatch18-KCp0.3-0.8BucketKC0.1BucketKC0.6BucketKC1.2RoofKCp0.1-0.27RoofKCp0.1-0.37DNV-CurveMudmat CFDPerforation0 10 20 30 40 50• No reduction applied in added mass when perforation is small. A significant drop in theadded mass for larger perforation rates. Reduction factor applicable for p

Simplified Method, Splash Zone - Hydrodynamic ForcesThe hydrodynamic force is a time dependent function of slamming impactforce, varying buoyancy, hydrodynamic mass forces and drag forces. In theSimplified Method the forces may be combined as follows:Fhyd2( FD Fslam) ( FM F)2• The structure may be divided intomain items and surfaces contributingto the hydrodynamic force• Water particle velocity andacceleration are related to thevertical centre of gravity for eachmain item. Mass and drag forcescontributions are then summarized :FM F M iiF D F DiiFMi and FDi are the individualforce contributions from eachmain itemDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 28

Simplified Method, Splash Zone - Load Cases ExampleThe static and hydrodynamic force should be calculated for different stages. Relevantload cases for deployment of a protection structure could be:Load Case 1Still water level beneath top of ventilated buckets• Slamming impact force, Fslam, acts on top ofbuckets. Inertia force to be included.• Varying buoyancy force, Fρ , drag force, FDand hydrodynamic part of mass force, FM arenegligible.Load Case 2Still water level above top of buckets• Slamming impact force, Fslam, is zero• Varying buoyancy, Fρ , drag force, FD andmass force, FM, are calculated. Velocity andacceleration are related to CoG of submergedpart of structure.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 29

Simplified Method, Splash Zone - Load Cases ExampleLoad Case 3Still water level beneath roof cover.• Slamming impact force, Fslam, acts on the roofcover.• Varying buoyancy, Fρ , drag force, FD and massforce, FM are calculated on the rest of thestructure. Drag- and mass forces acts mainly onthe buckets and is related to a depth, d, down toCoG of submerged part of the structure.Load Case 4Still water level above roof cover.• Slamming impact force, Fslam, and varyingbuoyancy, Fρ, is zero.• Drag force, FD and mass force, FM are calculatedindividually. The total mass and drag force is thesum of the individual load components, e.g. :FD= F Droof + F Dlegs + F Dbuckets applying correct CoGsDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 30

Simplified Method, Splash Zone - Load Cases ExampleDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 31

Simplified Method, Splash Zone - Static Weight• In addition, the weight inaccuracy factor should be appliedDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 32

Simplified Method, Splash Zone - DAFCapacity ChecksThe capacities of crane, lifting equipment andlifted object are checked as for lift in air. Thefollowing relation should be applied:DAFFMgtotalwhereMg : weight of object [N]Ftotal : is the characteristic total force on the(partly or fully) submerged object. Taken as thelargest of;F total = F static-max + F hydF total = F static-max + Fsnapor• Fstatic-max is the maximum staticweight of the submerged objectincluding flooding and weightinaccuracy factor• Fhyd is the hydrodynamic force• Fsnap is the snap load (normallyto be avoided)DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 33

Simplified Method, Splash Zone - Slack SlingsThe Slack Sling Criterion.• Snap forces shall as far as possiblebe avoided. Weather crietria shouldbe adjusted to ensure this.• The following criterion should befulfilled in order to ensure that snaploads are avoided:F0.9 hyd F static min• Fstatic-min = weight before flooding,including a weight reduction impliedby the weight inaccuracy factor.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 34

Simplified Method, Splash Zone - Results• Tables can becomputed givingan overview ofoperableseastates• Maximumallowable Fhydis derived frommax allowableDAF and theslack slingcriterion• Red results areaboveinstallation limit• ”Outside” meansnon-existentseastatesHydrodynamic force on object, FhydTz\Hs 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.02.0 12.24 Outside Outside Outside Outside Outside Outside Outside2.5 8.33 Outside Outside Outside Outside Outside Outside Outside3.0 6.14 20.45 Outside Outside Outside Outside Outside Outside3.5 4.79 15.54 32.45 Outside Outside Outside Outside Outside4.0 3.89 12.34 25.53 Outside Outside Outside Outside Outside4.5 3.29 10.19 20.89 35.40 53.71 Outside Outside Outside5.0 2.87 8.73 17.76 29.97 45.35 63.92 Outside Outside5.5 2.57 7.70 15.57 26.17 39.52 55.61 74.44 Outside6.0 2.35 6.92 13.90 23.30 35.10 49.32 65.96 85.006.5 2.16 6.27 12.53 20.94 31.49 44.18 59.02 76.017.0 2.00 5.72 11.36 18.92 28.40 39.79 53.10 68.337.5 1.85 5.24 10.34 17.17 25.72 35.98 47.97 61.688.0 1.73 4.82 9.46 15.65 23.39 32.68 43.52 55.918.5 1.62 4.45 8.68 14.32 21.36 29.81 39.66 50.919.0 1.52 4.13 8.01 13.17 19.60 27.31 36.30 46.569.5 1.43 3.84 7.42 12.16 18.06 25.13 33.37 42.7610.0 1.36 3.59 6.90 11.27 16.71 23.22 30.79 39.4410.5 1.29 3.37 6.43 10.48 15.51 21.53 28.52 36.5011.0 1.23 3.17 6.02 9.78 14.45 20.03 26.51 33.9011.5 1.17 2.99 5.66 9.16 13.50 18.69 24.71 31.5812.0 1.12 2.83 5.33 8.60 12.65 17.49 23.10 29.5012.5 1.07 2.69 5.03 8.09 11.89 16.41 21.65 27.6213.0 1.03 2.55 4.75 7.63 11.19 15.42 20.34 25.93DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 35

Simplified Method, Splash Zone - SummaryCheckNo slackslingsComputeF d, F m,F slam and F ρF hydApply• Object motion equal crane tip• Wave kinematics dependent onassumed Hs,Tz seastate• Different deployment levels• Structure divided in main itemsDAF withincapacityrequirementsDAFDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 36

Simplified Method, Splash Zone - SummaryThe simplified methodassumes that:• Vertical motion ofstructure is equalto the crane tipmotion.• The horizontalextension of thestructure is small.• Only verticalmotion is present.More accuratecalculations can beperformed applying:• Regular designwave approach(Ch. 3.4.2)• Time domainanalyses• CFD analysesDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 37

Content• Brief overview of relevant DNV publications• DNV Rules for Marine Operations, 1996,Pt.2 Ch.5 Lifting – Capacity Checks• Simplified Methods for prediction of Hydrodynamic Forceso in Splash Zone, DNV-RP-H103 Ch.4o in Deepwater, DNV-RP-H103 Ch.5DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 38

Deepwater Operations - ChallengesChallenges :• Static weight at crane tipincreases linearly with cablelength.• The resonance period of thelifting system increases withcable length. Dynamic forcesmay increase due to resonantamplification induced by thevertical crane tip motion.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 39

Dynamic Forces – Vertical resonanceDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 40

Simplified Method, Deepwater - AssumptionsDNV-RP-H103 Chapter 5 includes a simplifiedmethod for estimating dynamic response oflowered object.The following main assumptions are applied:• the subsea structure is lowered intodeepwater and is unaffected by waveforces• the vertical motion of crane tip andsubsea structure dominates → othermotions can be disregarded• Offset due to current forces isdisregarded• Heave compensation systems are nottaken into accountDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 41

Case Study – Main Data• The subsea structure mass is 97 tonnes• Water depth is 3000 m• The crane cable is a conventional steel wire• No heave compensation systemDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 42

Case Study – Crane Tip Motion• Lift at side ofcrane vessel• Wave heading15° off bow• RAO in heave,pitch and roll arecombined inorder to find thevertical motion atthe crane tip• Vessel’s naturalperiod in roll atT=9s dominatesDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 43

Case Study – Dynamic Load at Lifted Object• Comparison with anon-linear timedomainFE analysis• Dynamicamplification 20%higher at naturalperiod T 0 =9s• Dynamic amp. atT=1.5s due tolongitudinalpressure waves• No wave energy atT=1.5s, hencedeviation isacceptableCable length L=2750mDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 44

Case Study – Dynamic Load at Lifted Object• Transfer functionsfor dynamic loadin cable andcrane tip motionare combinedwith a wavespectrum S(ω)• Jonswap wavespectrum withHs=2.0m andTp=9s is applied• Most probablelargest responsefor dynamic forcein cable is foundby:A duration time t =30 minutesgives F d =530kN in this caseDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 45

Case Study – Dynamic Load at Lifted Object• Calculationsare repeatedfor a range ofseastates• Hs=2.0m givesacceptabledynamic loadsfor all waveperiods• Natural periodof the liftingsystem isT 0 =9sDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 46

Case Study – Dynamic Load at Lifted Object• Calculations arerepeated for arange of cablelengths• Max Fd for allTz values• Fd2250mdue to weight ofcableNon-operableseastatesDNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 47

Simplified Method, Deepwater - Summary DNV-RP-H103 chapter 5 contains a simplified method forestablishing dynamic loads and limiting weather criteria duringdeepwater lifting operations Most probable largest dynamic load in the lifting line is computedtaking into account dynamic amplification due to resonanceeffects The simplified method is well suited for common spreadsheetprograms or other computer software for engineeringcalculations.DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 48

.. Questions ??DNV Marine Operations' Rules for Subsea Lift Operations 29. November 2011Slide 49

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