The Pencil Buoy Method TM – Installation and removal of subsea ...

The Pencil Buoy Method TM –
Installation and removal of subsea
structures
Subsea Lifting Operations
Stavanger 30th November 2011
Henrik Mork, EMAS AMC
30.11.2011

Agenda
• Project references
• Pencil Buoy Method TM Overview
• Movie from installation
• Pencil Buoy
• Heave Compensator
• Aspects from T&I
• Advantages
• Future developement
• Conclusion
30.11.2011

Reference projects for wet tow
Project Installations
Removals
Heidrun 1 template 1 template
Vigdis
2 protection structures
Snøhvit
4 templates
1 control distribution unit (CDU)
foundation
1 pipeline end manifold (PLEM)
foundation
Norne
1 pipeline end manifold (PLEM)
module
3 templates
Summary:
Langeled
1 subsea valve station (SSVS)
• Over 10 years in service
Oseberg
Delta
Ardmore
West Don
Kittiwake
1 template
1 SAL buoy suction anchor
1 SAL buoy suction anchor
1 SAL buoy suction anchor
• 9 project with Installation/
removal in Norwegian and
UK sector
• 17 structures installed or
removed
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The Pencil Buoy Method TM
1. Inshore pre-rigging
• Transfer of structure from inshore crane to
vessel winch
• Transfer from vessel winch to Pencil Buoy
2. Subsurface tow
• 3-4 kts towing speed
3. Lowering to seabed on site
• Transfer of structure weight from Pencil Buoy
to vessel winch, via heave compensator
• Lower to seabed
30.11.2011

Installation
Link
30.11.2011

Installation, cont’
.
Target tolerances: +/- 2.0 m and +/-1,0º
As-installed tolerances: +/- 0,5 m and +/-0,5º
30-Nov-11 Aker Marine Contractors Page 6

Pencil Buoy
• Carrying Capacity: 250 / 400 tonne
• Weight: 55 / 80 tonne
• Height: 29.5 / 35 m
• Diameter: 4.5 / 5 m
30.11.2011

Heave Compensator
■ Waves vessel heave motion
■ System loads depends on structure mass
and added mass
■ Nitrogen compression wire out
■ Nitrogen expansion wire in

Heave Compensator cont’
■ Single wire routing
■ Cylinder stroke length: ± 2 m
■ Wire stroke length: ± 4 m
■ Separate nitrogen containers
7-Sep-07 Slide 9/20

Method Advantages
• No need for large deck space
• No crane required offshore
• Avoid pendulum motions in air
• Avoid slamming loads
• Accurate installation
30.11.2011

Important aspects from T&I viewpoint
• Landing velocity
• Target 1.0 m/s
• Damper design (for manifold installation)
• Drain hole capacity
• Rigging and lift point design
• Avoid spreader bar
• Lift points at top of template
• Rigging angle, target 50 deg to the hor. plane
• Pay attention to fatigue in lift point detailing
• ROV friendly shackle release system, grab bar location, marking
• DAF = 2.0
• None of the above imposes significant cost, if addressed during design
phase
Summary
Early involvement -> installation friendliness -> limited cost impact(if any)
30.11.2011

Further development
• 10 yrs ago:
Limited number of AHC crane vessels
Method was developed to handle large structures in harsh
environment with simple equipment, with an AHT as offshore vessel
• Today; availability of AHC crane vessels has increased
• Next step in development:
• Better utilization of the lifting capacity of an AHC crane vessel for
wide cargos, by combination with the Pencil Buoy Method
• Step 1 and 2 as before
• Step 3: Transfer weight from Pencil Buoy to AHC crane, complete the installation
with AHC crane. The crane heave compensator is used instead of the extra deck
heave compensator

Concluding remarks
• Cost effective and safe
• Developed, tested and improved over
several years
• Offered for a wide range of module
weights and shapes
• Good and simple system
• Can be further developed
7-Sep-07 Slide 13/20

Thank you for
your attention!
7-Sep-07 Slide 14/20