A methodology of nondestructive testing for cracking in PHWR feeder pipe

In order to develop a long-range nondestructive testing technology to detect a flaws in the PHWR (Pressurized Heavy Water Reactor) feeder pipe, dispersion curves for the feeder pipe were calculated. After STFT (Short Time Fourier Transformation) of acquired signals, it was confirmed that the modes of ultrasound were L(0,1) and L(0,2) modes. The circumferential notch with 20% of wall thickness was detectable with L(0,1) mode at the frequency of 500 kHz. However, the axial notches were not able to resolve the signal. On the contrary, an axial notch in the bent region was detectable with same experimental condition. It seems that the initial L(0,1) mode are converted to another modes at the bent and the converted waves were sensitive to the axial notch at the bent. The rocking guided wave technique was attempted to evaluate the axial notch quantitatively. It was found that -the wave generated by rocking guided wave was Rayleigh wave (surface wave) after review of acoustic velocity. This technique is relative simple and easy to implement at the field inspection, but it is expected heavy radiation exposure for the examiners and only possible to the accessible bent pipe. It is suggested that the long-range guided wave method be applied to general examination of feeder pipe and rocking guided wave method be useful for accurate location and size of the flaws.