High-tech Layer Shields Turbines from Super Heat

2008-Mar-29 | New materials are the key to success when it comes to boosting the energy efficiency of conventional power plants. Micrometer-thin layers developed by Siemens experts in Mülheim and in Munich increase the heat resistance and service life of these high-tech blades — and higher combustion temperatures mean higher efficiency. The protective layers are also used in the largest gas turbine in the world, which is currently being tested at the Irsching location, near Ingolstadt, Germany. In combination with a steam turbine, efficiency of over 60 percent is the target. In comparison with the previous most efficient plant, this corresponds to a saving of roughly 40,000 tons of CO2 annually.

A two-layer system ensures the super gas turbine’s durability, with a ceramic layer acting as heat insulation and making the record-breaking turbine resistant to combustion temperatures of over 1,400 degrees Celsius. The adhesive layer beneath, between the metal of the turbine blade and the ceramic coating, ensures a long service life and protects the metal against oxidation. Recently, Siemens experts have begun adding one or two percent rhenium to the adhesive layer, which previously consisted of a mixture of cobalt, nickel, chromium, aluminum, and yttrium. This improves its mechanical properties and provides a total service life of 25,000 hours — six times longer than pure metal would survive in the hot flow of the combustion gases.

A special inspection technique guarantees that the turbine blades are absolutely flawless, allowing them to withstand the extreme operating conditions. With this technique, an optical triangulation method developed by Siemens Corporate Technology creates a fully three-dimensional image of the surface, detecting even the tiniest hairline crack or bump. The information reveals the thermal load, among other data. If UV lighting is used in combination with the measuring system, the tester can even obtain information on the position and size of otherwise invisible cracks. The data collected in the process can be evaluated and used to improve the design and manufacture of turbine blades in the future.