Penetrant testing of products made of porous materials is hampered by the fact that the pores having exit to the surface cause the same (or even greater) intensity of luminescence as the defects do. It deteriorates the sensibility and reliability of the defects detection.

We have proposed the method for suppression of the background luminescence. This method can be implemented in two ways. According to the first way, the product is impregnated with the auxiliary penetrant (specially selected liquid) to the saturation state [4]. Then the auxiliary penetrant is removed from the surface to be controlled and the product is impregnated with the basic penetrant (ordinary penetrant used for the penetrant testing) in the ultrasonic field in the regime of the ultrasonic capillary effect.

In the second case, the product is penetrated with the auxiliary penetrant to the near saturation state when the cracks are filled only partially. Then the product exposure at the air for 1-10 minutes and putting the basic penetrant.

Due to this method the cracks will be filled with the basic penetrant to grater extent than the pores and this will provide the reduction of the intensity of the background luminescence in comparison with the intensity of the luminescence of the defect trace.

The tests of the developed method for defect revealing in the products of nitride ceramics have shown that the use of the preliminary impregnation with the auxiliary penetrant allows to increase the relationship between the luminescence intensity of the defect trace and background luminescence intensity 1.5-2 times and to provide the revealing of defects on the porous materials with the opening width more than 2 micron.

REFERENCES

1. P. P. Prokhorenko, N. P. Migun, Introduction into the Theory of Penetrant Testing, Minsk, p. (in Russian), 1988
2. P. P. Prokhorenko, N. P. Migun, A. P. Kornev, The Influence of gas dissolution and diffusion in Defects on Sensibility of Penetrant Testing, 6th European Conference on NDT, NICE 24-28 October 1994
3. P. P. Prokhorenko, N. P. Migun, Calculation of Penetrant Testing Sensibility for Powder Developer, Non-destructive Testing, Proceedings of the 4th European Conference, London, UK, 13-17 September, 1987, Vol. 4, p. 2774-2782
4. N. V. Dezkhunov, P. P. Prokhorenko, I. V. Stoicheva, Method of Suppression of the Background Luminescence for Products of Porous Materials, Defectoscopia, N 10, p. 62-67, 1983 (in Russian)