Precision. Aggregate is dropped hundreds of meters with guided tubes to prepare |
bed. (Photo courtesy of Norsk Hydro)
...during the run to shore. A complex route through natural passageways and around obstacles has been chosen to reduce the spans of pipe suspended across low spots in the terrain. The seabed also is being prepared by remotely operated excavators and crushed rock emplacement. The first template and manifold was lowered into place Aug. 19.
Skanskas Eiken says working with Hydro has been good for Skanska. "Its a very good platform for developing the organization and inspiring Skanska Norway...inspiring, but also hard. Its hard to work with a very demanding customer." Strict attention to safety protocols has been one of Hydros demands, although the attention did not succeed in preventing the death of a Skanska worker July 28 in an accident while grouting fissures in a cavern. A crane fell in another incident, but no one was injured.
Construction on the plant has been aided by integrating all design and engineering into a single 3-D model built with Vantage Plant Design and Management System (PDMS) software from the Aveva Group plc, Cambridge, England. As elements are validated, engineers can lock features in the complex maze of foundations, the 12 km of utility trenches, 150,000 cu m of condensate storage caverns and the water intake and outfall tunnels. They began releasing construction documents at the 27% design stage.
|Manifolds are being set 3.6 km apart.|
Engineers also were able to quickly determine the "mass-balance" elevation plane for the 700-m x 1-km footprint of the plant. Virtually all of the 2 million cu m of material moved by 2,000 blasts and 20 months of excavation, including 600,000 cu m of crushed rock, will be used in construction. "Nothing is hauled off site as debris. Even the vegetation cleared has been mulched," says Rolf Jacobson, Hydros civil, structural and architectural supervisor. But even more importantly, adherence to the model and the early design commitments has let site clearing and infrastructure excavation be performed simultaneously.
click here to view diagram
"I cant start detailing a foundation until I know the load and design of the equipment that will be placed upon it," says Jacobson. "But the model, which is being worked round the clock in Oslo and Mumbai, India, is updated nightly and as engineering progresses, the status codes on elements advance from Stage 1, to 2 and then 3," says Jacobson. "When we reach S-3, I can issue drawings. Weve had no serious changes." He adds, "Norsk Hydro has taken the risk. Were pushing the schedule."
Jacobson says Hydro has adapted its 3-D plant-modeling practices from its offshore projects. It is incorporating for the first time underground-systems engineering because this "platform" is on land. "We never before had underground systems in the model," Jacobsons says. "Its an offshore project brought onshore."
Load calculations for foundations and structures go to extremes, literally. Pit depths are engineered for the lateral load foundations must resist if other plant components explode. Foundations are sized so equipment will not overturn, preventing an orderly shutdown. Depending on function, some buildings are designed to open relief vents in under 45 milliseconds, and others to sway and bend. "For three years weve been thinking on it," Jacobson says.
It takes 100,000 12-m sections of 40- and 44-in. pipe to form the long pipeline run from Nyhamna to England. Named the Langeled Pipeline, work is well under way, starting with the 540 km run from Easington, England to the Sliepen Platform, near the halfway point to Norway. The gas can be mixed there with gas from other wells, or diverted to Europe, as needed. A 33-km segment of pipe to start the trek from Nyhamna also is now being laid.
|Plumbing the Depths. Pipelaying brings the line to the Sleipen Platform, about half way to Norway from England on June 11. Gas can be mixed there with other wells or diverted to Europe. (Photo courtesy of Kim Laland/Statoil)|
Two of the worlds largest pipelaying vessels are involved in the work and more than 1 million tons of steel are being used for the pipe, which is painted on the inside and coated on the outside with asphalt for corrosion protection and covered with concrete for additional weight.
Hydros next innovation for the proj-ect involves experimentation with another piece of sea-floor equipmenta compressor to help keep Ormen Langes line pressure up after about 15 years, when it is expected to decline. The compressor will operate off electrical power and aggregate the gas from several wells. If Hydro is successful in developing the unit, it will eliminate the need for an offshore platform for the life of the Ormen Lange field. That could change the way offshore gas developments are done in many parts of the world.
"It has the potential to save maybe half the cost of a typical floating platform," says Stokset. "If we do that, it will be a technological leap for the whole industry."