Novel X-ray Backscatter Technique for Detecting Crack below Deposit

We are studying X-ray backscattering technology with uncollimated X-ray irradiation (XBU), which is expected to detect a crack below deposit without removing the deposit and to inspect a large area of an object surface at once. As a first step of this study, we evaluated fundamental XBU performances in the viewpoint of application to Visual Testing (VT). Using a pinhole X-ray 2D camera and an industrial X-ray tube, we measured artificial cracks in stainless steel test pieces. Those results were as follows. (1) The artificial slits of greater than 0.05 mm width were detected. Theoretical analysis showed that the targeted 0.025 mm width crack can be detected by increasing an intensity of irradiation X-rays. (2) From the analysis based on the experiments, crack-detectable deposit thickness is 0.7 mm when the crack is 0.025 mm width and 0.5 mm depth and the deposit is metal-oxide deposit of 1.2 g/cm. (3) An artificial stress corrosion cracking in a curved test piece below artificial deposit of iron oxide was detected. From its measurement time, requirement for the X-ray generator to apply XBU to VT was evaluated. In the case of setting the X-ray irradiation head within 50 mm from an object surface, about 38 mA of the X-ray tube current is required to measure a crack in 5 minutes (one third of the VT measurement time including removing the deposit).