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LAKE RESCHEN POWER PLANT TRUSTS IN DUCTILE CAST-IRON PIPE SYSTEM

The old hydroelectric power plant Guido Donegani in Glurns near the Reschen Pass is even today considered a technical ­masterpiece in power plant construction.

Especially impressive is the extensive system of pressure lines and pressure tunnels, ­through which nearly every water resource of the region is directed into Lake Reschen. This power plant system has thus been drawing water from a total of seven bodies of water from both sides of the valley since its commissioning in 1949. For the ­power plant operator Hydros GmbH, the time had now come to renew a section of this feed water system and to trust completely in the know-how of the Tiroler Rohre GmbH in the process.

Known as the topmost level for the run-of-river power plant Kastelbach, the hydroelectric power plant Guido Donegani is one of two power plants that are fed by the 116 million m³ Lake Reschen.
The sophisticated waterway system of the so-called “Reschen lakes concession” extends from the tributary valleys of the Vinsch­gau through Lake Reschen down to Schluders. The Etsch, with its inflow streams Arundabach, Meltzbach, Marienbergbach, Zerzerbach, Punibach and Saldurbach, plays a central role for the Lake Reschen reservoir. A considerable expanded flow rate of up to 22 m³/s is achieved for power plant operations. The works water falls from a ­waterfall drop of 586.2 m onto 2 horizontal twinned Pelton wheels. The power plant produces 248.74 GWh in an average standard year.

LAYING PIPES IN THE TUNNEL
Following a pipe break on the right shore below Lake Reschen, the renovation of the old sheathed concrete line was already commenced with in 2015 and was renewed piece by piece. As with the first section previously, the operating company Hydros GmbH this year once again decided in favour of ductile cast-iron pipes from Tiroler Rohre GmbH, which are exceptionally well-suited for the rocky terrain thanks to their high compressive and fracture strength. Another advantage is provided by the BLS®/ VRS® T-connection, which guarantees rapid laying of pipe regard­less of the weather. “Winter comes very early at 1,500 metres above sea level and the snow remains on the ground for a long time. Every­thing has to happen fast”, says Christoph Obkircher, sales manager at TRM for Italy. This year around 600 metres of pressure lines were replaced. In the process, the ­situation for the routing through rocky ground resembles that of the previous year. However, the special feature here is the 180 metre long tunnel through which the old concrete pipe was also laid. “The difficulty was in the fact that the new pipe, in contrast with the old concrete pipe, was twice as heavy”, says Obkircher. This presented a real challenge for the laying team. The local construction company had previously refurbished the tunnels for the most part, poured a concrete floor in the approximately 1.75 m high and approximately 1.75 m wide tunnel and then sealed its top side. This created the prerequisites for installing the pipe. Nonetheless, the handling of the 2,500 kg ­pipes proved to be difficult.
The pipes were laid on galvanised steel cradles in the tunnel itself. “A special vehicle was built for laying in the tunnel in order to lay pipe by pipe together with the steel cradles. The spatial conditions in the tunnel were just adequate for allowing one person each to the left and the right of the pipe to find space to connect the cast-iron pipes with the TRM plug-in sleeve system. “If the tunnel were any smaller, we would have had to dimension the pressure line differently”, Obkircher adds.

THE CONNECTION
The quick and problem-free laying of the pipe is also made possible by the socket joint restrained against longitudinal forces. Whereby a weld bead at the narrow end of the cast-iron pipe ensures the mechanical shear and tensile strength and the interior of the coupling is designed according to the principle of the 2-chamber system. The TYTON® seal is inserted into the first chamber. Lubricant is then applied to the seal and the narrow end and the cast-iron pipes are pushed together with a 1.5t chain tackle block. The 14 locking segments planned for the DN1000 are then deployed. These are inserted by way of a so-called “window” and pushed around the entire coupling. It is also possible to loosen this connection at any time. This simple but clever socket joint can in any case withstand pressure of 16 bar and tolerates a maximum permitted tensile strength of 1,560 kN. This is appropriate for the area around Lake Reschen with a maximum operating pressure of 10 bar. When the narrow end and the pipe are properly connected, the line is still bendable to 1.5° even at DN1000, which offers considerable room to manoeuvre. Thanks to the sophisticated socket system, the exertion of force when pushing together is still many times less than with other manufacturers, even with large pipe diameters. Time-consuming follow-up work, such as welding, weld bead checks or the retroactive application of a surface treatment are also unnecessary. The trench can thus be closed again immediately after the laying of the pipe.

THE INSTALLATION OF THE PIPES
The ductile cast-iron pipe from TRM, as the name suggests, is malleable. The malleability prevents the formation of cracks. Precisely this fulfils the difficult requirements in the steep Alpine terrain with its rocky substrate. “A shear and tensile strength-proof connection is thus imperative for this reason”, says Obkircher. The pipe itself is made of spheroidal iron, with a ferritic basic matrix, and is manufactured in a centrifugal process. Inside it is coated with grouting and a cement mortar sheath out­side ensures the retention of mechanical properties. “The grain size of the bedding material can thus be very high, whereby it can in some cases even be dispensed with, which saves time and effort throughout the entire construction phase”, according to Obkircher. An experienced team manages about 8 pipes per day, which is around 48 metres. A total of 4 different bends can be chosen from, whereby the repertoire of TRM includes a complete series of piping fittings and components, suitable for any application.

COMPLETION IN SPRING 2017
The second section was now completed in the context of refurbishment for the connection of the Etsch with the tributaries Arundabach, Meltzbach, Marienbach and Zerzerbach. The second of three stages was thus realised. “The tunnel required many measures that made more rapid work progress impossible. The last section will be tackled in spring”, says Obkircher. After passing through the tunnel, the TRM cast-iron pipe ends in the old pump house above Lake Haider at 1,450 m above sea level. It is waiting to be connected in spring to the Etsch, which is very rich in water resources. In order that Lake Reschen can once again be supplied with valuable water, like in the past 58 years.


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