Energy generation without leakage in the Swiss Alps: Story in the 2/2022 Issue of the German Trade Magazine 'KE-NEXT'

Focus Switzerland. “When leaks were found at the Limmern pumped storage plant in 2019, I was consulted as an ex- pert for hydraulic line systems. The damage analyses showed that cracks had formed in some of the cutting ring tube fittings.” This was caused by the permanent vibrations acting on the hydraulic lines in the power plant. Leak-free under extreme conditions 24° tube connectors with cutting ring are generally very durable and are regarded as the universal standard for connecting metric tubes with outside diameters bet- ween 4 and 42 mm in hydraulic systems reliably and without leaks. “For the application with the extreme conditions at the Limmern pumped storage plant, how- ever, it would have been better to use a different joining solution – tube forming – from the outset,” summarises Uwe Bröllos. He recommends STAUFF Form, which was specially developed for high-pressure applications and strong vibrations by STAUFF, the German manu- facturer and developer of all components for hydraulic line systems. The principle: The STAUFF Form machi- ne is used to reshape the tube end so that a positive connection is created during installation with a con- ventional fitting body and a union nut. The only con- ceivable leakage path is additionally secured with a Viton seal. So while STAUFF Form only changes the shape of the tube material, a cutting ring connection is achieved when a metal ring with two edges cuts into the tube surface. This incision into the material limits the vibration resistance. In contrast to this, the forming system has a higher tear-out strength, which offers a safety benefit under extreme conditions – like the strong pressure surges and vibrations as at the Lim- mern pumped storage plant. This is a crucial aspect for mechanical engineering and plant engineering manu- facturers in safety-critical fields, such as ship building, offshore plants or cranes and lifting devices. Operational safety and environmental protection Oswald Hauser, Head of the Mechanical Engineering division at Kraftwerke Linth-Limmern AG, chose STAUFF Form together with his maintenance team in 2020. Since then, the stainless-steel cutting ring fittings have gradually been replaced with formed connections. “Our focus is on operational safety, leak protection and prevention of environmental damage. The stainless-steel lines carry up to 18,000 litres of oil that must not leak into the plant or nature.” The use of highly durable tube connections also substantially reduces the service and maintenance costs. After all, several dozen kilometres of lines have to be checked at the Limmern pumped storage plant in tightly spaced maintenance intervals. The water is drained as required and can drive four turbi- nes with a total capacity of 1000 MW. Image: Axpo Power The STAUFF Form Evo is completely based on standard components. Image: STAUFF 1 Maschinenkaverne 2 Teensformatorenkaverne 3 Schieberkammer 4 Zugangsstollen 1 mit Standseilbahn Tierfehd-Kavernenzentrale (Los A1) 5 Zugangsstollen (Bestand) Chalchtrittli-Lirnmernstaumauer 6 Zugangsstollen 2 7 Fensterstollen 8 Sondierstollen 9 Oberwasserdruckstollen 10 Wasserschloss 11 Druckschächte 12 Unterwasserdruckstollen 13 Ein- und Auslaufbauwerk 14 Hochwasserentlastung und Grundablass 15 Bauseilbahn 2 Ochsenstäfeli-Muttsee ke NEXT · 02 2022 33 fluid · 01 2022 The Stauff Form EVO tube forming system is completely based on standard compo- nents and is available with the Viton seal. Image: Stauff The water is drained based on de- mand and can drive four turbines with a total power of 1000 MW. Image: Axpo Power AG Tube forming instead of cutting rings 24° tube co nectors with cutting ri gs are usually highly resistant a d ar egard d to be the universal standard for r liably connecting metric tubes with external dia- meters between 4 and 42 mm in hydraulic systems with- out leaks. “For the extreme conditions in the Limmern pumped st rage plant, however, it would have bee ad- visable to use a different connection solution from the outset – tube forming.” Uwe Bröllos recommends Stauff Form, which was developed specifically for high pres- sure applications and strong vibration loads by Stauff, the German manufacturer and developer of all compo- nents for hydraulic line systems. 1 Machine cavern 2 Transformer cavern 3 Valve chamber 4 Access gallery 1 with funicular Tierfehd– cent al cavern station (section A1) 5 Access allery (existing) Chalchtrittli– Limmern retaini g struct re 6 Access allery 2 7 Window gall ry 8 Probing gallery 9 Headwater pressure gallery 10 Surge tank 11 Pressure shafts 12 Underwater pressure gallery 13 Inlet and outlet structure 14 Flood relief and bottom outlet 15 Constructio cableway 2 Ochsenstäfeli– Muttsee lake barrage 2474 m Update for Stauff Form In 2021, Stauff updated its forming system that had been used success- fully in international mechanical and plant engineering since 2015: The previously used metal ad pt r ring wi its p rma ntly connect- ed elastom r s al was replace with a “simple” FKM (Viton®) seal. This is less expensive and therefor of particular interest to applications involving larger quantities, without safety being compromised. Both systems are still available and are formed with the same machines. For he changeover to Stauff Form EVO, ly the tool sets have to be re- placed and a software update has to b installed.