2017 年 83 巻 853 号 p. 17-00148
Replacement of a damaged pipe is important to prevent an accident caused by the pipe. The major damage of the pipe in long-term use is pipe wall thinning. Thus, identification techniques of the location and the thickness of the pipe wall thinning are necessary to decide the appropriate time to replace the pipe. The ultrasonic testing (UT) and the radiographic testing (RT) are currently mainstreams in nondestructive inspections. However, the UT requires the surface preparation of the pipe, and the RT has the risk of the radiation leakage. This study has developed a novel technique of nondestructive identification of location and thickness of pipe wall thinning by using magnetic sensor. This technique aims at only nonmagnetic pipes, and estimates the location and the thickness of the thinning part in the pipe by using the measurement data of the magnetic flux density when the electric current is applied into the pipe. Furthermore, the measurement sensitivity of the magnetic flux density is improved by setting the high magnetic permeability material around the magnetic sensor. In order to verify the validity of the proposed technique, numerical simulations and actual experiments were performed by using specimens with several patterns of the location and the thickness of the thinning part. The results show that the direct analysis values agreed with the measurement data. The inverse analysis results show that the estimated values of the parameters to evaluate the thinning part successfully agreed with the correct values in most of the cases in this study. It is believed that the proposed technique can be applied to practical situations.