Turbine pipeline for the Seebachschleife hydropower plant

Seebachschleife is located in the municipality of Bayerisch Eisenstein in the Regen district of Lower Bavaria, Germany. As far back as 1934, the glassgrinding factory in Seebachschleife – now a listed building – was using water power as its energy source. In 1997 the hydroelectric power plant changed hands and some innovative changes have since been made to the turbines and pipelines. For example, a new, 3 km long DN 500 power station pipeline has been installed to supply water to the turbine building.

Stresses in the pipe wall:
tangential stresses σt due to internal pressure and axial stresses σa due to the positive locking push-in joints of the pipes.

Waiting for installation:
DN 500 pipes with BLS® socket joints, wall thickness class K14. High-alumina cement lining and zinc-aluminium coating with a reddish brown epoxy finishing layer.

Ductile cast iron pressure pipeline 

This ductile cast iron pressure pipeline carries water from the Großer Arbersee lake (approx. 935 m above sea level) to the turbines at Seebachschleife (approx. 640 m above sea level). The lower part of the pressure pipeline runs through the hamlet of Seebachschleife for a length of around 300 m. The altitude difference of approximately 295 m produces an operating pressure of about 30 bar; also the route of the pipeline makes a sharp change of direction at this point. To take up the pressure fluctuations and to provide an additional safety margin, the pipes and pipe joints in this area needed to be designed for a pressure of 40 bar. The developers decided to use ductile cast iron pipes (GGG) with positive locking BLS® socket joints, which can absorb both the tangential stresses st caused by the internal pressure of 40 bar and the axial stresses sa produced by the positive locking joints of the pipes.

288 m of GGG pipes in nominal size DN 500 with BLS® socket joints in wall thickness class K14 (minimum cast iron wall thickness 12.2 mm) were installed. The pipes are lined on the inside with high-alumina cement and coated on the outside with zinc-aluminium and a reddish brown epoxy finishing layer. They were produced specifically for this project and delivered within 4 weeks. This meant that the tight time schedule set by the client of around 8 weeks from placing the order to completion of the construction project was able to be met.

A 30° change of direction of the power station pipeline in Seebachschleife with a MK 500/30° fitting and BLS® socket joints, lined and coated with epoxy blue.

Once the ductile iron pipes had been laid alongside a forest road, the backfill material is compacted layer by layer.