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Smart
Leg - Float-over-Deck Installation
The Need
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The installation of decks for large offshore platforms frequently require the
use of large barge crane vessels because of their size and weight. However, if the
platform needs to be located in a place with long period swell conditions, the cargo barge
will suffer from large amplitudes that will difficult the mating of the deck's legs with
the piles. |
Barge Entrance into the Jacket
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The Technology
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Developed and patented by ETPM
the principle of the Smart-Leg technology is based on using passive hydraulic devices to
neutralize the vertical movements of the barge and to transfer the deck weight from the
cargo barge to the piled jacket structure. The Smart-Leg jacks allows the mating of each deck leg onto the corresponding
jacket pile to take place at the precise time when the deck leg vertical speed is zero,
therefore eliminating the kinetic energy and the risk of impact. The deck mating is
completed in a few seconds less than the swell period. During the abandonment phase,
the deck can be removed by reversing the operation (Labbé, 1998.)
Hydraulic jack assemblies are fitted on the
deck above the jacket legs. A cargo barge carries the deck on a special support called
Smart-Shoes. The barge is positioned in front of the jacket. A set of devices called
Smart-Fins are first deployed to establish contact at the four corners of the jacket and
to contain the barge in the space allowed for mating. The Smart-Fins are equipped with
hydraulic shock absorbers that will reduce the aft and fore motion of the barge to under
25 millimeters. Afterwards, Smart-Fenders are used to eliminate the sideways motion of the
barge. (Labbé, 1998.)
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Stopping Cargo Barge surge and sway with
Smart-Fins and Smart-Fenders
Stopping Deck with Smart-Leg jacks.
Cargo Barge pull out after collapsing the
Smart-Shoes
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When the cargo
barge carrying the deck has been positioned inside the jacket, the jacks are activated to
deploy extension pipes in order to establish contact with the jacket top of piles. The
jack extension pipes extend and contract as the deck moves up and down according to the
swell. A check-valve located between the jacks will close and lock the deck at the peak of
its motion when the velocity of the deck legs and the kinetic energy forces are zero. At
this point the deck and barge are totally immobilized with the deck load shared by the
jacket and the barge. The final load transfer is achieved by ballasting the barge and
collapsing the Smart-Shoes. |
The Benefits
- After the deck is installed all the
hydraulic devices can be easily retrieved to be ready for another project. A regular
float-over operation could be done in less than 6 hours.
- The Smart-Leg system should be expected to
handle decks in the 3,000 tonne to 40,000 tonne range. The heavier the deck the easier the
installation since the heavier decks would have less motion.
- The acceptable limit in terms of waves is
usually no more than 2.8 meters in a long period of 15 seconds.
- The cost and risk of lifting and installing
heavy decks in places with long swells is considerably less than using heavy-lift barge
cranes.
The Status
- A float over deck installation was
succesfully completed offshore Nigeria in June 1997 by McDermott-ETPM for the EKPE Gas
compression platform. The barge preparation was done in 3 days. The float-over operation
was done in 6 hours. This was the first operation made with the Smart-Leg Technology.
- This technology was succesfully used in a
totally different project. The completion of the bridge crossing the strait between Prince
Edward Island and New Brunswick in Canada. On November 1996 the Smart-Leg system was used
to positioned the heavy bridge spans (192 meters long and 8,000 tonnes weight.)
- The system won the Offshore Northern Seas
Innovation Award in Stavanger in August 94.
- Saipem, an international contractor within the oil and gas
industry is studying a similar system
with the Danish Hydraulic
Institute.
Points of Contact
- Michael Mugnier-Pollet. McDermott-ETPM S.A.
32, Avenue Pablo Picasso TSA 76001 92754 Nanterre Cedex France. Phone: 33 (0)1 40 97-6143.
Fax: 33 (0) 1 40 97 6555.
References
- Labbé, J.P., Allègre, V., Volker J.,
Agdern, F. 'Ekpe Gas Compression Project - Float-over Deck Installation,' 1998
Offshore Technology Conference, Houston, Texas. May 1998.
- McDermott-ETPM S.A. 'First Smart.Leg
Float Over Operation on EKPE field in Nigeria for MOBIL,' Photo Report. June
1997.
- 'The GTM-ENTREPOSE Group completes the
bridge crossing the strait between Prince Edward Island and New Brunswick, Canada
(20/11/96).' News Update. Groupe
GTM.
- 'ETPM's smart float-over solution.'
ONS News. March 1998. Offshore Northern
Seas, web site.
- EKPE Project. J.Ray McDermott, web site.
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
LHM06
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