Today, the energy demand of mankind is growing with each passing day, and the need for construction and operational stability of all power plants including thermal power plants is increasing. Therefore, many non-destructive testing (NDT) methods have been developed and used in safety analysis of power plants worldwide. X-ray inspection, ultrasonic inspection and magnetic particle inspection are typical ones. But these methods do not provide a guarantee for the safety of structures since they are not suitable for regular full-scale inspection of various structures in the industrial sector due to their high cost of inspection, artificial magnetization process of objects to be tested, complex operating conditions and high time consumption.
Recently, metal magnetic memory (MMM) method is widely used in the world for its cost-effectiveness, easy operation, time saving and high sensitivity. In particular, MMM method has two advantages. First, fatigue failure occurring in stress concentration zones (SCZ) can be diagnosed and prevented. Second, the inspection device is effective for regular whole inspection of different structures like power plants for its simplicity and high inspection speed.
Based on the metal magnetic memory test principle and the data on the sensor type, Ryu Yong Chol, a researcher at the General Assay Office, has selected sensor material for weak magnetostatic field measurement and made an SCZ inspector.
First, he determined the optimum excitation method for highest sensitivity, the influences of various factors on the characteristics of the sensor and the method of measuring the leakage magnetic field. Then, he conducted a tensile test and inspection on different specimens to verify its reliability.
The results show that MMM device enables fast inspection of ferromagnetic structures and diagnostics and prevention of fatigue failure in SCZ, which is impossible with other non-destructive testing methods.
© 2021 Kim Chaek University of Technology