NDTnet 1998 Aug, Vol.3 No.8

Abstract

Gas turbine blades and vanes are operated in a high temperature and corrosive atmosphere. Due to this the lifetime of the blades is limited. In order to increase the lifetime different measures are applied. One important measure is the application of a protection layer against oxidation and corrosion. Despite of this, the generation of cracks is unavoidable. For livetime assessment the crackdepth is the most important parameter. So it is if vital importance to have an accurate nondestructive technique for the crackdepth determination.

We decided to apply an eddycurrent technique addapted to this specific problem. Because of the relevant crack depth in the order of 1 mm, an excitation frequency in the range from 1 MHz to 5 MHz was selected. Due to the small crack distance in the order of one mm an eddycurrent probe with a diameter in the same order of magnitude is demanded.

In order to determine the crack depth we applied a reference object made of the same material and provided with several notches of different depth. The EC-signals were evaluated according to their amplitude and compared with the EC-signals obtained from the real cracks. Interpolation of the measured values delivered the crack depth. The results were validated afterwards by a destructive me/allographic examination. The results obtained with both methods don't differ more than 20 %. Experimental results will be presented.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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