One of the world’s biggest geothermal power plants is currently under construction in southeastern California: After completion in 2012 the “Hudson Ranch” project will have a capacity of almost 50 megawatts – enough to light 100 football stadiums at once.
Or in this case to supply the city of Phoenix, Arizona with electricity. And the good thing is, it’s completely friendly to the environment, because geothermal power plants don’t cause any pollutant emissions. And nickel alloys of ThyssenKrupp VDM make them work.
Steam-spouting geysers in Iceland are an illustrative example of the power of geothermal energy, the heat stored beneath the surface of the earth. The deeper you go, the warmer it gets. And the greater the demands placed on the material used to make geothermal pipes. On average the temperature rises by roughly three degrees Celsius for every 100 meters of depth. With today’s technologies and materials, this environmentand climate-friendly energy resource can be used practically everywhere, which is why geothermal ranks among the most commonly used renewable energies. In a geothermal power plant, heat is converted into electric power by means of a turbine. Water is piped through an underground heat reservoir. The heat it collects is used to drive a turbine, which produces electricity via a generator. The cooled water is then piped through the heat reservoir again to complete the cycle.
The pipes are made from nickel alloy quarto plates, which display extreme resistance to corrosion and fatigue in demanding applications and environments. Because the high geometric requirements involved in pipe production are particularly difficult to meet with corrosion-resistant high-temperature nickel alloys, ThyssenKrupp VDM’s materials know-how and longstanding experience in rolling technology are vital in this application. In addition, in the middle of last year the Werdohl-based company installed a new, longer spray pickling line in its Siegen hot rolling mill, enabling it to produce twelve meter long quarto plates. This saves a huge amount of effort and expense in producing and assembling pipes from the plates. “This investment has allowed us to extend our product range significantly. We can run higher pickling temperatures, the process is substantially improved, and ThyssenKrupp VDM is now also able to process titanium and zirconium products on the line,” says Hanno Gerich, superintendent of ThyssenKrupp VDM’s Siegen and Altena plants.
“The pipe market is moving from six meter to twelve meter lengths wherever technologically and economically feasible,” explains Winfried Sterzl, Vice President Sales Oil & Gas at ThyssenKrupp VDM. But while the aim is for ever longer and thinner-walled pipes, the laws of physics impose limits. Above a certain length depending on wall thickness the pipes become unstable. Twelve meters also comes close to the length limits for road transportation.
Yet the advantages of 12 meter pipes are clear: Pipes in geothermal power plants are subjected to extreme mechanical, thermal and corrosive stresses. These requirements can only be met by a high-nickel material like ThyssenKrupp VDM’s Nicrofer 6020 hMo (Alloy 625). It also has to be remembered that the welds between pipes are always the weakest links in the chain. Extending the pipe sections to 12 meters cuts the number of welds by half and therefore considerably reduces the risk of premature failure of the pipe system,
as well as avoiding additional manufacturing costs. ThyssenKrupp VDM is exploiting these advantages
worldwide as a supplier of high-quality materials for demanding projects not only in the geothermal field but
also in the oil and gas industry. With its help, the lights can soon go on in Phoenix without causing harmful
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