Saving the CF6 air seal

CDP now repairable
Superior repair solution

Advanced repair: Lufthansa Technik has developed an innovative repair method that eliminates the need to scrap an expensive engine component. The compressor rear frame stationary CDP air seal in the CF6-80C2 engine can now be repaired, a solution clearly superior to purchasing a spare part, both financially and technically. 

Avoiding problems

Lufthansa Technik's Engine Parts and Accessories Repair (EPAR) unit has a whole series of advanced repairs available, by means of which the cost of an engine overhaul can be reduced substantially. A current example is the stationary CDP air seal of the CF6-80C2 turbofan.
The CDP seal is used to seal the core engine bearing housing against compressed air and is designed as a knife edge – Honeycomb seal with three stages comprising two knife edges each. This design has proved problematic during overhauls in the Lufthansa Technik shop. Replacement of the honeycomb which the knife edges of the seal enter during operation does not merely require that the braze layer is removed. Because the braze filler material diffuses into the base material, this layer also has to be removed. As a result, the wall thickness of the remaining honeycomb land is already below the permitted minimum limits on the first overhaul.
 

Repair process and benefits

Because of this the CDP, which has a price tag of around $100,000, is effectively scrap. When it came to developing the new repair method, the responsible development department therefore focused its attention on the objective of enabling multiple repairs to be carried out. These greatly increase the service life of the component. The repair itself entails removing the honeycomb land and welding in a prefabricated spare part alternative detail (SPAD) by using electron beam welding. Because of the design of the LHT fabricated SPAD, there is a sufficient reserve to allow multiple repair cycles. Lufthansa Technik now has another technique in its armory for containing the costs of an engine overhaul. The customers can also benefit from the financially and technically superior solution. Due to the possibility to perform this repair beyond an engine overhaul expensive CDP can be saved from scrapping and bring enormous cost savings for the engine parts customers.