Development of the advanced phased array UT technique for accurate sizing of cracks in the nozzlewelding
西田 純一朗 Jun-ichiro NISHIDA 川浪 精一 Seiichi KAWANAMI 井手尾 光司 Mitsushi IDEO 松浦 貴之 Takayuki MATSUURA 千種 直樹 Naoki CHIGUSA 平野 伸郎 Shinro HIRANO 瀬良 健彦 Takehiko SERA
Dissimilar Metal WeldingMatrix Phased ArrayPhased ArrayUltrasonic TestingUT Sizing
Recently, preventive maintenance tasks for welding of safe-end nozzles of reactor vessels and steam generators of PWRs in Japan had been carried out sequentially. Before the maintenance tasks, inspection services were carried out and several crack indications were found by eddy current testing (ECT). These indications were found in the welding which made b y 600 series nickel base alloy and evaluated as stress corrosion cracks which were oriented to the axial direction of the nozzle. Then investigations to evaluate the depth of cracks were carried out by ultrasonic testing (UT) from inner surface of the nozzles. However they were difficult to evaluate the depth of cracks due to the high attenuation of the ul trasonic propagation caused by large grain structure of welding. And also it was required high resolution near surface region for accurate sizing. Therefore development of advanced phased array UT techniques specialized for the sizing at this portion was carried out. This paper reports the development status and verification test results. Firstly simulatio ns of the ultrasonic propagation in the welding were carried out to optimize beam profiles of phased array probes. Next prototype probes were manufactured and verification tests were conducted to evaluate the accuracy of depth sizing. It is shown that the developed techniques have high sizing accuracy for artificial stress corrosion cracks in the welding.