## 4 Conclusions  
In this study, we developed an automated device for real-time internal defect detection in pipeline welds by combining passive RT techniques using conventional films with digital RT technology. Furthermore, this study developed an automated inspection device using DRT technology, facilitating seamless integration with automation for real-time feedback and the automatic detection of internal defects in welded pipe sections. Conservative theoretical models and FLUKA simulations were employed to predict the path and intensity of radiation scattering, enabling the development of a device capable of automatically inspecting hazardous radiation sources on the circumferential welds of pipes. The findings of this study were as follows:  
1. Using gamma rays instead of X-rays offers advantages for placing inspection equipment in narrow spaces between pipes. However, gamma ray radiography quality is generally inferior to that of X-rays. Specifically, the Se-75 radiation source can produce high-contrast images for thinner materials compared to Ir-192 and meets DRT quality standards. 2. The theoretical calculation results from the conservative approach and the FLUKA simulation results differed by approximately 5 m from the safety distance and the error rate was small. However, concerning the leakage angle of the tungsten collimator through micro processing and the theoretical shielding area, the actual measured  
Figure 11: Derivation of radiation dose measurements through field installation pipes. (**a**) Appearance of dose measurements in field-installed pipes. (**b**) Result of dose measurements in field-installed pipes. radiation dose and safety distance differed considerably. This phenomenon could be attributed to differences in the amount of scattering in the transmission path of radiation and different variables such as absorption and reflection. 3. When applying the atomic regulation authority's conservative safety constant in the theoretical formula, the corresponding distance was 21.6 m if the target dose of 1 uSv/h was satisfied. Because of using the inspection device with the supplemented shielding conditions through FLUKA simulation to test pipes installed in the field, a value of approximately 2.15 uSv/h was measured at 12 m. When converting this value using the inverse square law, the target dose of 1 uSv/h could be satisfied at approximately 17.5 m. This phenomenon could lower dose values measured in the field when compared to those in the simulation results because of the additional shielding effect of the surrounding structures. 4. Through this study, we developed equipment capable of automatically inspecting welds by rotating them using radioactive sources. To further develop the equipment in the future, the following research directions and needs were identified: (1) Prolonged exposure to radiation in Digital Detector Arrays (DDAs) can introduce noise that may adversely affect image quality. Although this study confirmed satisfactory performance for pipe thicknesses around 10 mm, it is necessary to assess potential degradation in image quality with pipes of maximum thickness. (2) X-rays are essential as radiation sources that can produce the optimal quality of digital radiography tests. It is expected that there will be a need to develop inspection devices using small-sized X-rays that can be integrated into the equipment. (3) Lastly, it is expected that the development of an automatic inspection device using a video-type inspection method will be necessary to improve inspection efficiency. There will still be difficulties due to the image distortion of test results but research to overcome these and establish optimal conditions is expected to continue to be necessary. Conceptualization, D.-S.K. and J.K.; methodology, D.-S.K. and S.-H.H. ; software, S.-U.H. ; validation, D.-S.K., S.-H.H. and S.-U.H. ; formal analysis, J.K. and S.-U.H. ; investigation, J.K.; resources, J.K.; data curation, D.-S.K. and S.-H.H. ; writing--original draft preparation, D.-S.K. and S.-H.H.