Many damages of the piping system in the nuclear power plants have occurred due to the vibration fatigue induced by the mechanical vibration of pumps and so on. One of the preventive measures for the problem of vibration is the evaluation of vibrational stress, which is the methods using the strain gauge and the accelerometer. However, these evaluation methods require highly specialized skills and many man-hours, and nuclear plants are awaiting the development of vibration-measuring techniques and evaluation techniques that are easy to perform and produce accurate results promptly. The purpose of this study is the development of the method and the device measuring the vibrational stress directory using the laser displacement sensor. The proposed method evaluates the vibrational stress as follows: Three laser displacement sensors measure the displacement of the piping induced by vibrating, and the strain of the piping is calculated from the difference among the sensor-measured displacements to determine vibrational stress. The measurement equipment isn’t direct contact with the piping evaluated, can be easily reduced in size, and can realize quick and accurate measurement. This paper describes the concept of the proposed evaluation method of vibrational stress in the piping system using three laser displacement sensors, along with its theory and measurement procedure. And then, refer to the proposal of the evaluation method of torsional vibration using six laser displacement sensors. This paper also compares the stress values calculated based on the cantilever vibration identified by this method and the stress values calculated based on material mechanics, and discusses the applicability of the method in actual plants.

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