The pipeline installation ship "Castoro Sei" welded a total of 16,650 sections of pipe measuring 12 meters long to complete the Grane to Sture transport system. Hydro's contractor for the work offshore was European Marine Contractors.
The Grane to Sture system - designed by Norwegian engineering company Reinertsen - crosses several other pipelines and cables and is laid into a furrow of stone and gravel just meters away from the Oseberg to Sture pipeline.
The greatest sea depth the pipeline traverses is 355 meters - through the Norwegian Trench. More than 110,000 tonnes of rock and gravel was dumped onto the most difficult seabed areas to establish a foundation for the pipeline, says project controller Terje Thorsen, Hydro Technology and Projects.
"The work was very demanding, but it went exceptionally well." Thorsen is especially satisfied to have avoided using divers to join the pipe sections. It was also possible to move the drilling rig "Scarabeo 6" to and from the field without interrupting the pipe-laying operation. It saved NOK 20 million and even more important, the risks associated with diving operations was avoided.
Now that the offshore and land-based parts are connected, the pipeline will be filled with water, scoured with a "pipe pig" and pressure-tested with sea water at the Sture terminal.
The pipline-installation vessel "Castoro Sei" has already started laying the 50 kilometer and 18-inch diameter gas pipeline from Grane to Heimdal, says Per Harald Hansen, pipeline activities manager in the Grane project. Installation work is expected to take 14 days. Plans call for both pipelines to be finished with pressure-testing by October 1.
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