Work on installing a 6 km steel pipeline from Capolago to Bissone has been under way for about one year. This pipeline, which transports natural gas at a pressure of 5 bar, is laid in the lake. A main gas distribution network is already in place to supply consumers in the Lugano and Mendrisiotto regions. The aim is to make distribution of this energy vector to users safer and more efficient. The tender issued by Aziende Industriali di Lugano (AIL) SA led to the engagement of three specialised companies as a consortium. These are Josef Muff AG for the pipeline construction, Willy Stäubli AG for the underwater work and Comal.ch SA as construction manager.
Construction of the 6,000 m pipeline is a careful step-by-step process. Three individual 100 m sections of steel pipe (diameter: DN 300) are welded together directly on the lake shore. A rail system is then used to transport the 300 m sections into Lake Lugano. Boats carry the sections to the welding pontoon; one after another, they are welded to the existing section and lowered to the lake bed. The sections must be pressure tested every 100 metres. Before the pipes are installed and submerged, the 20 kV insulation test must be completed and the pipe must be mechanically protected; these procedures must be performed carefully in accordance with precise work instructions.
One of the most challenging aspects is the geometry of the lake shore, which makes it difficult to install the 32 m initial section. As the lake bed is less than 10 m below the surface at Capolago, it was first necessary to dig a trench so that this section of the pipeline could be lowered and installed. The S-shaped section was welded together from two cold-bent components. It then had to be lifted at the correct angle and welded onto the existing straight section of pipe. Swivelling the S-section over the prepared trench in the lake without touching bottom or overloading the crane was the difficult part of the operation. At the same time, the boats on the lake had to align the existing 400 m length of pipe that was to be welded to the S-section. The interaction between the boats and the crane called for maximum precision.