David A. Raulerson

Economical approach to automated eddy current inspection

Eddy current inspection has long been recognized as a very sensitive and highly reliable means of detecting surface cracks in aerospace components, especially gas turbine engines. A number of factors such as equipment cost, false rejections, and throughput impacts have limited its application in the industry. All of these factors ultimately relate to the cost associated with the inspection. In the Air Force products produced to the ENSIP or PPSIP criteria, fracture critical components with relatively small flaw sizes are typically inspected as part of the production process and at their predetermined overhaul interval. The use of a hard inspection interval that requires the engine be disassembled and inspected at predetermined points in its life is fundamental for Air Force engines. In both the production and overhaul environment, dedicated facilities that utilize fully automated systems have become the norm. Fully automated systems utilize as many as seven axes and typically cost well over 1 million dollars per system require highly trained individual s to program them for new inspections. Typically, these systems are housed in their own facility which also adversely affects cost effectiveness. Once in operation, these systems can achieve crack sensitivities as small as 0.005 inches deep. To use these systems, the parts must be fully disassembled and cleaned prior to inspection. In the case of very small flaw size requirements, the parts are frequently polished to achieve an acceptable surface condition. These systems have been used very effectively in the maintenance of modern fighter engines.