조대 결정립 스테인레스강에서 위상배열 초음파를 이용한 결함 평가

Abstract

Ultrasonic inspection of austenitic stainless steel components had to face major difficulties due to the coarse grained structure of these materials. Attenuation losses and structural noise were encountered, which limits the performances of defect detection ability, mostly in terms of degraded signal-to-noise ratio and poor sensitivity. To overcome such problems, many studies had been achieved in many countries. This study consists of 2 main ideas. Firstly, ultrasonic beam simulations were done with various design factors of phased array probe to obtain the best condition of detecting the defects in coarse grained stainless steel. By using this results, a phased array probe with the best design factors was made. In order to compare the new probe and conventional phased array probes, Measurements of the sensitivity were performed over stainless steel specimen of coarse grained structure containing artificial reflectors. The signal-to-noise ratio of the new probe was about 3 times greater than that of the conventional phased array probe. Secondly, a new method was suggested to improve the accuracy of a defect sizing in case of inspecting defects of coarse grained stainless steels with phased array probes. Ultrasonic beam simulations were done with various attenuation factors to infer the sound pressure at defects in the material with unknown attenuation factor. The size of defect was derived from this sound pressure. The new method of was very useful to evaluate the defects size in coarse grained stainless steel with a high attenuation factor.