Gas from the North Sea is processed at Karsw, Western Norway, before it isexported to the European Continent. The pipelines are placed in a 600 metresconcrete tunnel, consisting of 5 bridge elements, at the shore approach.
Cracks developed in the foundations and the elements shortly afterinstallation, and they appeared to be caused by environmental loads.
To carry out a permanent repair, substantial engineering work to modify thedesign was necessary.
The repair was carried out in 1991 and 1992, and included the following underwater work:
Repair of cracks in the concrete.
Installation of new lateral support bearings and reinforcing the foundationsfor lateral forces.
Installation of new flexible vertical bearings. These bearings weighed up to4.5 tonnes, and required jacking up 500 mm elements weighing up to 5000tonnes.
Gas transportation in the pipelines was never reduced due to the repair.
This paper describes the cause of the damages, the repair design and thecomplex underwater operations required to carry out the repair.
The shore approach at Kalsw is part of the Statpipe Transport System and isshown as Figure 1. This pipeline system transports rich gas from Statfjord, Gullfaks and Veslefrikk fields in the North Sea to the Karsw Gas Terminal inWestern Norway for processing. Dry gas is thereafter exported to the EuropeanContinent.
The Norwegian coastline is very rugged, and the bottom is most often rockywith large topographical variations. At Kalsw the problem of having unevenbottom was solved by taking the pipelines ashore in a 600 m long bridge tunnel. Figure 2 shows the tunnel approach with the bottom profile.