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MEK 4450Marine OperationsKværner ASA / DNV, Fall 2012
Installation of flexibles and cables
Typical productsRigid pipesFlexible pipesCables and umbilicals
Installation and installation analysesInstallation of end terminationsRegular layingSpecial challenges: shallow water, deep water, slopes, turns etcWaiting on weather
Typical product categories
PipeRigidFlexible
CableElectricUmbilicals
Beam theory. Axial loadCompressionBedning moment
Courtesy: Bredero Shaw
Courtesy: NKT Flexibles
Courtesy: Nexans
Courtesy: Nexans
Rigid pipe
Large diameterHeavyHigh laying tension
High bending radiusLarge deck spaceExpensive equipment
Some plastic deformation acceptableStraightening before over-boardingAvoid repeated plastic bending
Thermal insulation (wax formation)
Concrete weight layers (gas pipes)
Courtesy: Bredero Shaw
Flexible pipes
Low elastic bending radiusLess expensive laying vessels / equipmentMore competition
Separate layers forAxial loadOuter pressureInner pressure
Courtesy: NKT Flexibles
CablesPower cables and umbilicals
Smaller bending radius, lower unit weightLess expensive vessels / equipment
High densityHeavy load on a fully loaded vesselStructural capacity and vessel stability
Limited plastic bending
Courtesy: Nexans
Typical installation vessels
Installation vessel with horizontal tensioner and chute
Installation vessel with lay tower
Pipe lay vessel with reel and lay ramp
Pipe lay vessel with stingerDP vesselAnchor vessel
Pipe lay vessel with J-lay tower
Installation vessel with horizontal tensioner and chute
Aker Connector
Tensioner / Caterpillar
Used to pay in / out product, and to maintain/ support cable tension
Belts with pads press against the product
Sufficient force to Pull in and overcome friction over chuteSupport maximum cable tension (e.g. storm)
High tension + low radial load capacity => long tensioner / many pads
Internal friction in the cable may be lower than friction between cable and pads!
ChuteCable installation
Provides continuous support
Introduces vessel heading restrictions
At maximum design tensionChute structural capacityProduct integrity (bending + tension)Over-bending at tip of chute(top angle from analyses)
Installation vessel with lay tower
Scandi Neptune
Pertinacia
Seven Seas
Pipe lay vessel with reel and lay ramp
Pipe lay vessel with stinger
Stinger
Provides support for pipes
Rollers to reduce friction (=> point loads)
Stinger radius above elastic bending radius of pipe
Departure angle high enough to prevent over-bending
Avoid lift-up of pipe in stinger
Will impact vessel motion characteristics
NOTE: picture shows stinger in elevated, not operational mode
Pipe lay vessel with J-lay tower
Pipe sections raised into vertical
Vertical welding of pipe sections
Pipe tension supported by clamps
Installation analyses
Establish weather criteria and a plan for laying (laying tables)
Ensure robust and safe operations for personnel, equipment and flexible product
Low tension: over bending, axial compression, loop formationHigh tension: rupture, tensioner capacity, free spans
Ensure that all tolerances are accounted for
Determine and verify survival conditions
Installation analyses
Shore landing
Pull-in to shore
Shallow lay
Installation analysesUphill vs downhill lay
Downhill layMore flexible catenary (reduced risk of cable over-bending/compression)May cause high seabed tension and free spans
Uphill layLess flexible catenary (due to geometry) => reduced weather criteriaRisk of cable sliding downhill
Installation analyses
Laying in steep slopes
Difficulty in assessing where actual touchdown point is=> step-by-step analyses as input to operational procedures
Installation analyses
General considerations (analyses)
Deep waterHigh top tension, tensioner capacityCombined tension and bending at vessel interface
Curve laySliding of productLow lay tension (risk of over-bending/compression)Possible solution: Laying around preinstalled piles etc
Installation analysesInstallation of buoyancy elements
Step-by step analyses to Determine vessel movements vs. pay-out of pipe/cableEstablish procedure for attachment/lowering of clump weight
Main challengesOver-bending/compression at vessel interface due to buoyancy
Installation analysesPull-in to platform
Step-by step analyses to Determine lowering of pipe/cable from vessel vs pull-in to platform
Main challengesVessel positioning (available space)Seabed clearanceOver-bending at I-tube inlet
Survival conditionCutting of product
More critical for power cables and umbilicals
Installation of buoyancy elementsEstablish flexible ”S”- shaped configurationStep by step analysis to ensure product capacity while over boarding buoyancyAnalysis gives guidance in when to pay in / pay out after installationAnalyses: can the vessel maintain heading and position?