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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


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


Laying in steep slopes

Difficulty in assessing where actual touchdown point is=> step-by-step analyses as input to operational procedures


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?

Documents

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