Giant moves
How to move a 15-story oil and gas platform deck from its construction site to final location offshore.
With high seas and winds offshore, it is easier to construct oil and gas platforms on land. But then the challenge is moving the massive structures out to sea.
French company Technip has solved that problem with the float-over method, a technique for moving a platform deck to its permanent offshore location.
“Installing a large deck onto its jacket, or legs, using the float-over method is gaining popularity,” says David Emery, a Project Manager in the Offshore Platforms Product Business Unit of Technip. “This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single-piece installation by a heavy lift barge. Also, a high proportion of the pre-commissioning work can be completed onshore prior to load-out, significantly reducing the duration and cost of the offshore commissioning phase.”
Trelleborg’s Orkot material is used for low-friction pads that facilitate the “skidding“ of oil and gas decks onto transportation vessels and from them to the support structures at sea. The decision to use Orkot bearings was based on the material’s properties such as a high load capacity and compression strength, a low friction coefficient and strong chemical resistance. Demands are high in a float-over operation. The material must remain stable during the skidding operation, while continuously withstanding high loads during the time the decks are under construction, about two years.
(Click on the image for a larger view)
(fig. 1) Orkot material is used for low-friction pads that facilitate the “skidding” of oil and gas platform decks.
Loadout (fig. 2) – The platform deck’s journey begins at the construction site. The entire deck rests on Orkot pads laid on a runway to “skid” the deck onto its transport barge. Due to the pads’ low friction properties, hydraulic cylinders (stand jacks) can push the platform deck from the quay and onto the barge (fig.3).
The deck is then towed to the offshore installation site (fig.4).
Docking: Vessel Entry (fig.5) – At the installation site, the vessel is docked to the support structure, called the jacket.
Vessel positioning – At the final destination, the vessel is moored inside the jacket by eight mooring lines to ensure accurate positioning of the deck’s legs over the jacket legs.
Load transfer: The vessel is ballasted to make contact with the support structure and then prepared to transfer the deck.
Separation: After completion of the deck load transfer, a separation occurs between the deck and the vessel and the vessel is retrieved from the jacket using tugboats.
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