Fabricated of the SCC Reference Specimen for Increasing of In-Service Inspection Accuracy in Nuclear Power Plant

Abstract

To achieve the safety assurance of the nuclear power plants, in-service inspection have were enforced periodic for nondestructive test in weldment. Among them, the ultrasonic evaluation is widely used for the measurement of the defects. Generally, non-destructive inspectors have calibrated a UT machine using the reference specimen in the artificial cracks such as EDM, mechanical notch. As the reflected ultrasonic signal of real crack was detected amplitude value 50% lower than artificial cracks. Therefore, domestic ultrasonic inspectors have a little experience in measuring actual cracks generated in the nuclear power plant field, such as SCC(Stress corrosion cracks, below SCC) and thermal fatigue cracking. Accordingly, in order to improve the inspection accuracy of non-destructive inspectors during operation inspection of nuclear power plant structures, it is necessary to have a lot of experience in inspecting actual cracks.In this study, non-penetration SCC for using in educational specimen of the NDT inspector were fabricated by using the simulated nuclear environment system in base metal of STS 304 pipe. The size of the used pipe were 8 inch(80 sch., thickness 12.7mm). The end of the pipe was used a flange to simulating a fixed environment of the nuclear power plant structure. To accelerate the fabrication of SCC, a corrosive environment was composed by used a blending corrosion solution of the NaOH 1M and Na2S9-H2O 0.1M inside the pipe. The potential of hydrogen of the caustic solution was 14. The fabricated SCC was confirmed for crack size and shape by used UT and RT.