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Planer for MEK 4450Marine operasjonerKværner ASA, June 2011

Safety moment

Installation of flexibles and cables

Typical productsRigid pipesFlexible pipesCable and umbilicals

Configurations at platform

Installation aids

Installation and installation analyzesInstallation of end terminationsRegular laySpecial challenges: shallow water, deep water, slopes, turns etcWaiting on weather

Typisk produktinndeling

PipeRigidFlexible

CableElectricUmbilicals

Beam theory. Axial loadCompressionBedning moment

Courtesy: Bredero Shaw

Courtesy: NKT Flexibles

Courtesy: NexansCourtesy: Nexans

Rigid pipe

Large diamterHeavyHigh laying tension

High bending radiusLarge deck spaceExpensive equipment

Plastic deformations acceptableRightning before over boardingAvoid repeated plastic bending!

Thermal isolation (wax formation)

Concrete 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

Small radius, bending radius, unit weightLess expensive vessels / equipments

High densityHuge loads on a fully loaded vesselStructural capacity and vessel stability

Combined functionality

No plastic bending

Courtesy: Nexans

Theory slide. Installation aidsFlexible products are installed with various types of vessels equipped with means / tools for storage and controlled

over boarding of the products. Typically, the installation of rigid steel pipes requires bigger and more expensive vessels due to the huge space and holding capacities required during deck handling and installation.

In the following slides some typical examples are given. The first example show a laying vessels for electrical cables, where the cable are stored on a horizontal turntable. A horizontal caterpillar is used, where a tensioner will carry the weight of the product during overboarding. The vertical U- shaped unit at the side of the vessel is called a chute and prevent damages to the product when it goes into the sea.

We notice that the vessel is equipped with huge crane and a large open deck space. This means that the vessel may be used for other types of marine operations, like subsea lifting.

Separate slides display the installation equipment used by this vessel. We notice the belt with the orange pads forming the tensioner. The pads are pushed toward the cable to ensure sufficient friction. By running the belt the cable may be pulled in or out. The other slide shows the chute.

The next slide shows an alternative configurations, where the product are routed via a vertical or almost vertical laying tower during over boarding. The tensioner are mountd in the laying tower.

The third slide shows a vessels for pipe lay. Steel pipes are spooled on the enormous vertical drum in the centre of the vessel. The hold-back force is taken by the drum itself. In the stern part there are equipments for straightening out the pipes if there have been plastic deformations and a laying ramp for smooth transition of the product to the sea.

The last two slides shows two other options, particularly useful for laying of rigid pipes. The first case shows a vessel where the new pipe sections are welded to the pipe continuously during over boarding and laying. The huge stinger in the stern of the vessel will prevent critical over bending of the product,- plastic deformation is no longer acceptable as the product are going into the sea and there are no means for straightening it out again.

The last slide displays another alternative, where huge cranes are lifting pipe segments into a vertical “J-lay tower”. Here the segments are welded to the pipe being laid, again continuously during laying. This solution is particularily popular in deep water, while the previous solution may be more suited in shallow water.

Typical installation vessels

Installation vessel with horizontal caterpillar og chute

Installation vessel with lay tower

Pipe lay vessel with reel and lay ramp

Pipe lay vessel with stingerSemi-submersibleAnchor vesselDP vessel

Pipe lay vessel with J-lay tower

Installation vessel with horizontal caterpillar and chute

Aker Connector

Tensioner / Caterpillar

Used to pay in / out product, and maintain tension

Belts with pads pushed toward the product. Friction

Sufficient force to Pull in and overcome friction over chuteKeep cable in position in a storm

High tension + low radial load capacity = long tensioner / many pads

Internal friction may be lower than friction against pads.

ChuteCable installation

Smooth and even load distribution

Vessel heading restriction

At maximum design tensionChute structural capacityProduct integrity (bending + axial load)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

Stable support for pipes

Checking with analysis

Rollers to reduce frictionPoint loads

Stinger radius below elastic bending radius

Departure angle high enough to ensure smooth exit

Avoid lift-up of pipe in whole stinger

May impact vessel motion characteristics

NOTE: picture shows stinger in elevated, not operational mode

Pipe lay vessel with J-lay tower

Typical laying situation

Picture displaying vessel, water depth, product, and key geometric parameters

A salesman's death

RwH

HDw

H1sin

)sin(1

Dw

T

)sin(

)cos(1ln

RX

Bunnstrekk:

Toppvinkel:

Toppstrekk:

Avstand til touchdown:

hvorH = Horisontalt strekk i produktet i touchdown [N]w = Neddykket produktvekt [N/m]R = Minste bøyeradius over touchdown (i ”sag bend”) [m] = Produktvinkel med vertikalen [radianer]D = Vanndyp [m]T = Produktstrekk i øverste ende [N]X = Avstand mellom toppunktet og touchdown

Oppgaven var: en selger vil skaffe firmaet ditt en jobb der en kabel med gitt en gitt kabel skal installeres av et fartøy som tåler et gitt toppstrekk. Bør du gripe inn?

D=1000mW=10 kg/mR=5m

H=500N

=0.29 deg!

T=100500N

X=29.98m

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

Determine and verify survival conditions

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?

Steep slopes

Uncontrolled sliding of the productAxial compressionFree span formation

Anchor at top of slope?

Another anchor further down?

Other special considerations

Deep waterHigh top tension, tensioner and chute capacityCombined tension and bending at vessel interface

Curve laySliding of productLow laying tensionLaying around preinstalled piles etc

Power cable/umbilical from shore to offshore First end to shore:

Shallow conditions: Attach buoyancy elementsFloating

Onshore winch pulls in through ditches or tunnelsFriction, uncertain factor

Actual bottom topography, strong currents etc may lead to changes in vessel position. Robustness needed

Last end to shore:

More complicated floating

Power cable/umbilical from shore to offshorePlatform end:

Installation through platform J- tubes

Platform winch and forerunner through J- tubes

Coupling of power cable / forerunner at vessel deck.

Pull-in through J- tubes by platform winch.

Challenges:

Plans for vessel positions changed due to wind, platform managers and other unsteady phenomenon.

Floating platform offset

Clash with mooring lines, other risers etc

Over bending at start of J tube

Power cable/umbilical from shore to offshoreInstallation of buoyancy elements:

A “S”- shaped cable configurations at platform may be required.

Buoyancy elements in final stages

Use of clump weights or sea bed abnchoring may also be required

Power cable/umbilical from shore to offshoreChallenges

Compression / overbending near termination of buoyancy elements, touch down etc

Clump weight tangles up

Analyses to determine vessel movements and clump weight

Power cable/umbilical from shore to offshoreSubsea termination

Heavy end termination for subsea plug-in

Bending restrictor or similar at neck

Focus on bending moments at neck

Lowered by the cable: head fall over

Lowered by crane more controlled, but requires separation

Analysis Reveal need for crane Determine required separation between crane tip and

termination during lowering Calculate design loads for product loading