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09.04.2008 
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 Mühlheim 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.
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