Norway's Den norske stats oljeselskap AS (Statoil) has let contract to ABB Offshore Technology AS, Sandnes, Norway, to develop a giant subsea riser base for gas exports from Aasgard field in the Norwegian Sea.
The base will connect risers from Aasgard B gas production semisubmersible to a 700-km, 40-in export trunk pipeline extending from beneath the platform to Kaarsto terminal in Norway.
The 40-in. riser base will be much larger than any similar design to date and is expected to cost much less than the alternative: a fixed riser platform in 300 m of water estimated to cost 1-1.5 billion kroner ($150-225 million).
The riser base will house valves and connections to the 40-in. trunkline and six 10-in. risers in a structure 60 m long by 20 m wide and weighing 700 tons in total.
A 40-in. subsea pig launcher will project from one end of the base like a scorpion's tail, an ABB official said. The pig station will be lifted and lowered from a vessel or from Aasgard B.
The base will incorporate a 40-in. diverless subsea connector, which will be an adaptation of the well-established Grayloc connector that so far has been made for offshore operations only in diameters up to 13.5-in.
However, ABB has supplied Grayloc connectors for pipe sizes of more than 40-in. for the onshore power generation industry.
The ABB official said, "The challenge will be to bring a known technology into an unknown dimension. With this contract, subsea technology has taken a giant step."
ABB's engineering and development work will be carried out under a 15 million kroner ($2.25 million) contract, due for completion in October. An engineering, procurement and construction contract will be put out to bid in the fall.
Statoil recently let contract to Kvaerner AS, Oslo, to build Aasgard B (OGJ, Feb. 10, 1997, p. 30). Since then, Kvaerner has let a subcontract to South Korea's Daewoo Heavy Industries to build the hull.
The 17,000-metric ton hull will be delivered to Stavanger in August 1999 for fitting of topsides. Hull construction cost will be $85 million.
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