Underwater pipelines in SwitzerlandCustomer/Project: Underwater pipelines in Lake Zug and Lake Lauerzer
Dimensions (mm)/Steel grade: 273.0x10,0 / St 37.0
Order volume: 6+3 km
Special features: Underwater pipeline, depth 140m
In 2005, an ambitious project was started in Switzerland to connect "Innerschwyz" (central Switzerland) to the natural gas network. The energy providers in the cantons of Zurich, Zug und Schwyz agreed to work together on the project.
The required pipelines are to be laid over land and under water and linked up to the areas around Zug. The biggest challenge was the construction of two underwater pipelines. A 3-km long pipeline was laid across Lake Lauerzer in January 2006. The advantage of doing this in winter was that the lake was then very calm, although work did have to be stopped for a short period when it froze.
The second underwater pipeline was laid across Lake Zug by the end of August 2006. Pipes from Salzgitter Mannesmann Line Pipe, measuring 273.0 x 10.0mm, were used in both pipelines. The St 37.0 grade pipes were provided with a PE coating together with the additional protection of a reinforced fibre cement coating. This combination of materials gave the pipes the necessary weight to counteract buoyancy. At the same time the pipeline had to be able to resist the tensile and bending loads to which it was subjected as it was lowered to the bed of the lake. This necessitated the use of high quality material, backed up by a considerable level of know-how on the part of the pipe layers. Very few companies had the experience needed to sink a pipeline to a depth of 140 metres under the very difficult ground conditions in Lake Zug. Josef Muff AG (to be reached at http://www.muff.ch via internet), which has decades of experience in laying pipelines under extreme conditions, was awarded the order.
Groups of 8 pipes, each 16 metres long, were welded together to create strings 128 metres long. Floats were attached to the strings, which were then towed onto the lake. The strings were welded together on a floating pontoon to create the complete pipeline. GPS positioning, divers, survey boats, camera monitoring and above all experienced professionals were the prerequisites for embedding the pipeline in the lake bed in the desired S shape with the correct elastic bend radius. Great care had to be taken, as any error would have resulted in the loss of the entire pipeline. The work also had to be carried out to a tight schedule, so that the lake could be handed back on time to tourists, water sports enthusiasts and the local population. The use of a professionally installed underwater pipeline is the safest and environmentally friendliest, non-land-consuming means of gas transportation. Fortunately the Swiss have lots of lakes.