Automated ultrasonic inspection technique for main coolant pipes

As ultrasonic wave propagation properties specific for cast stainless steels are well-known, a number of researches on their experimental procedures and computer simulation have been progressed. On ultrasonic probes, for measures on scattering and damping at crystal grains, it is developed or recommended to use ultrasonic waves with relatively low frequency and convergent effect of ultrasonic waves in materials based on large oscillators and transmit-receive crossover systems. And, some researches on improvement of SN ratio based on signal processing on space averaging method, split spectrum method, and so on, are under development. In special, as a part of works on PISC (Program for the inspection of steel components), a large scale round robin test using cast stainless steel welded specimen is carried out to clarify inspection technology and procedure effective to the material. Under results on these R and Ds and verification works, in this study, was developed a large two oscillators probe loaded a large spherical oscillator with 76 mm in diameter at both transmitting and receiving sides, for probes suitable for ultrasonic inspection of coarse grain materials such as cast stainless steel used for main coolant pipes of PWRs. The probe can effectively transmit ultrasonic waves to aimed positions in the material, by convergent effects of both the spherical and the two oscillators. By mounting the probe onto a drive mechanism with local water immersion part developed in special, to perform automated ultrasonic inspection. And, the obtained inspection data enabled defect distinction easier by using their image displays. (G.K.)