Eddy Current Inspection of Turbine Blades.
Technical rept. Aug 69-Mar 71,
GENERAL AMERICAN TRANSPORTATION CORP NILES ILL GENERAL AMERICAN RESEARCH DIV
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This report presents the results of a nondestructive field inspection technique which will detect cracks in the leading and trailing edges of jet engine turbine blades. Various nondestructive inspection methods were considered and experimentally evaluated. Field and lab test data is presented. It includes response characteristics, speeds of inspection, and micrographs of typical cracks detected in the turbine blades of built up rotors from various engines. The system is capable of detecting cracks down to 0.020 inch in length, 0.0005 inch wide, and 0.005 inch deep. On built up rotors of an engine having 108 cleaned blades per stage cracks could be detected at an inspection rate of one stage in 15 minutes. The penetrant system could detect cracks at an inspection rate of one stage in 1 hour and 50 minutes. The good sensitivity to cracks using eddy currents can be explained on the basis of surface magnetic oxides. The signal response is much greater to the oxide-included cracks than to a clean crack. The ease of operation, speed of inspection of built up rotors, and excellent crack detection sensitivity of the eddy current system make it attractive for field maintenance inspection of turbine blades. It is recommended that several such systems, with appropriate application instructions, be provided to maintenance to allow an extended field evaluation of the technique. Author, modified-PL
- Test Facilities, Equipment and Methods
- Jet and Gas Turbine Engines