Development of wall thickness estimation by scattered gamma-ray energy

In recent years, many plant facilities have been aging and require appropriate maintenance. To perform proper maintenance, it is necessary to evaluate the integrity of piping and other components. However, conventional inspection methods for pipe thinning detection, such as ultrasonic inspection method and eddy current method, may require the removal of heat-insulation or restrict the installation conditions of inspection equipment. Therefore, we proposed a new non-destructive inspection method to detect pipe wall thinning by energy analysis of scattered gamma rays. The proposed method based on the phenomena that the energy of scatted gamma rays varies with the number of scatterings, even when the final scattering angles are same. Large objects, i.e. thicker object, are expected to have more events with higher number of scattering. This method is expected to eliminate the need to remove pipe insulation during the inspections. Experiments were carried out at the Cobalt Irradiation Facility at Nagoya University with multiple thicknesses of steel plates and a CdTe detector. We have experimentally confirmed that an increase in plate thickness causes a difference in the measured spectrum of the scattered gamma rays. This fact showed that the thickness estimation is capable within the steel thickness range of 3mm∼15mm. (author)