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MEK 4450
Marine Operations
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Presenter name, location, date etc.
Kværner ASA / DNV, Fall 2012

2. Installation of flexibles and cables
Typical products
Rigid pipes
Flexible pipes
Cables and umbilicals
Installation and installation analyses
Installation of end terminations
Regular laying
Special challenges: shallow water, deep water, slopes, turns etc
Waiting on weather

3. Typical product categories
Pipe
Rigid
Flexible
Cable
Electric
Umbilicals
Beam theory.
Axial load
Compression
Bedning moment
Courtesy: Nexans
Courtesy: NKT Flexibles
Courtesy: Bredero Shaw
Courtesy: Nexans

4. Rigid pipe Large diameter High bending radius
Heavy
High laying tension
High bending radius
Large deck space
Expensive equipment
Some plastic deformation acceptable
Straightening before over-boarding
Avoid repeated plastic bending
Thermal insulation (wax formation)
Concrete weight layers (gas pipes)
Courtesy: Bredero Shaw

5. Flexible pipes Low elastic bending radius Separate layers for
Less expensive laying vessels / equipment
More competition
Separate layers for
Axial load
Outer pressure
Inner pressure
Courtesy: NKT Flexibles

6. Cables Power cables and umbilicals
Smaller bending radius, lower unit weight
Less expensive vessels / equipment
High density
Heavy load on a fully loaded vessel
Structural capacity and vessel stability
Limited plastic bending
Courtesy: Nexans

7. Theory slide. Installation aids
Flexible products are installed with various types of vessels with equipment 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 large space and high tension capacity required during deck handling and installation.
In the following slides some typical examples are given. The first example shows a laying vessels for electrical cables, where the cables are stored in a horizontal carousel. A horizontal tensioner is used that carries the weight of the cable during laying. The chute over the side of the vessel provides support and prevents damage to the cable as it is over-boarded.
We notice that the vessel is equipped with a big crane and a large open deck space. This means that the vessel may be used for other types of marine operations such as installation of subsea modules.
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 configuration, where the cable is routed via a vertical laying tower during installation. The tensioners are vertically mounted in the laying tower.
The third slide shows a vessel for installation of small diameter rigid pipe (typically < 12” or 16”). Steel pipes are spooled (and deformed plastically) on the large vertical drum in the center of the vessel and installed over a lay ramp. The ramp may be tilted, typically to support a pipe lay angle of degrees. A tensioner that supports pipe lay tension is positioned on the lay ramp, while the reel ensures back-tension. The lay ramp also includes a straightener and a welding/x-ray station.
The next two slides show installation vessels with stingers, typically used for installation of large diameter rigid pipes (> 16” or 20”). Pipe sections (typically 12 m long) are continuously welded to the pipe string during laying. The large stinger at the stern of the vessel ensures that the pipe is not plastically deformed as straightening is not possible.
The last slide displays a typical J-lay vessel for installation of large diameter rigid pipe in deep water. Pipe segments are lifted into the vertical “J-lay tower” by use of specialized cranes, and then welded to the pipe string during laying.

8. 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 stinger
DP vessel
Anchor vessel
Pipe lay vessel with J-lay tower

9. Installation vessel with horizontal tensioner and chute
Aker Connector

10. 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 chute
Support 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!

11. Chute Cable installation Provides continuous support
Introduces vessel heading restrictions
At maximum design tension
Chute structural capacity
Product integrity (bending + tension)
Over-bending at tip of chute (top angle from analyses)

12. Installation vessel with lay tower
Seven Seas
Scandi Neptune
Pertinacia

13. Pipe lay vessel with reel and lay ramp

14. Pipe lay vessel with stinger

15. 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

16. Pipe lay vessel with J-lay tower
Pipe sections raised into vertical
Vertical welding of pipe sections
Pipe tension supported by clamps

17. 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 formation
High tension: rupture, tensioner capacity, free spans
Ensure that all tolerances are accounted for
Determine and verify survival conditions

18. Installation analyses
Shore landing
Pull-in to shore
Shallow lay

19. Installation analyses
Uphill vs downhill lay
Downhill lay
More flexible catenary (reduced risk of cable over-bending/compression)
May cause high seabed tension and free spans
Uphill lay
Less flexible catenary (due to geometry) => reduced weather criteria
Risk of cable sliding downhill

20. Installation analyses
Laying in steep slopes
Difficulty in assessing where actual touchdown point is => step-by-step analyses as input to operational procedures

21. Installation analyses
General considerations (analyses)
Deep water
High top tension, tensioner capacity
Combined tension and bending at vessel interface
Curve lay
Sliding of product
Low lay tension (risk of over-bending/compression)
Possible solution: Laying around preinstalled piles etc

22. Installation analyses
Installation of buoyancy elements
Step-by step analyses to
Determine vessel movements vs. pay-out of pipe/cable
Establish procedure for attachment/lowering of clump weight
Main challenges
Over-bending/compression at vessel interface due to buoyancy

23. Installation analyses
Pull-in to platform
Step-by step analyses to
Determine lowering of pipe/cable from vessel vs pull-in to platform
Main challenges
Vessel positioning (available space)
Seabed clearance
Over-bending at I-tube inlet

24. Survival condition Cutting of product
More critical for power cables and umbilicals
Installation of buoyancy elements
Establish flexible ”S”- shaped configuration
Step by step analysis to ensure product capacity while over boarding buoyancy
Analysis gives guidance in when to pay in / pay out after installation
Analyses: can the vessel maintain heading and position?