Thermal Shock and Cyclic Loading of Ceramic Parts in Stationary Gas Turbines

Abstract

A further increase in the efficiency of stationary gas turbines operating in the combined cycle process could save a huge amount of fuel costs while sharply reducing the output of environmental pollutants. Higher effective turbine inlet temperatures are therefore a requirement for the future. This goal can be reached by applying uncooled ceramic parts of high temperature resistance. Possible candidates are the combustion chamber and transition duct lining, stator vanes and rotor blades.

Ceramic parts are loaded with thermomechanical stresses that are caused by temperature gradients. An emergency shut-down in particular leads to a gas temperature decrease of more than 800 K within one second. Together with a very high heat transfer coefficient, this leads to a tensile stress of several hundred MPa. This thermal shock has to be withstood more than 100 times during the extremely long service time of 100000 h demanded for a stationary gas turbine.

Advanced ceramic materials seem to be suitable for short-term application but for long-term use subcritical crack growth by thermal cycling may be a hazardous failure mechanism. To provide sufficient reliability, a high quality standard in components production, excellent high temperature properties and a ceramic specific design methodology including life time prediction based on comprehensive test results are necessary.