Development And Testing Research On Nondestructive Testing System Based On Magnetomechanical Effect

Ferromagnetic materials have been widely applied to many kinds of equipment in service such as oil and gas transmission pipeline,tank pressure vessel and so on,because of their good mechanical,mechanical properties and low cost.These devices are in need of long time work in harsh temperature and high pressure environment.In the long service period,the materials would be failure due to corrosion,fatigue,stress and deformation.If the defective components could not be timely found,they may cause huge economic losses or even disastrous consequences.Therefore,it is necessary to detect the early damages of ferromagnetic materials.The ferromagnetic materials early damage detection system was developed in this thesis based on the magnetomechanical effect.The main contents are as follows.Firstly,the magnetic domain of ferromagnetic materials and the magnetization mechanism are explained from the microscopic scope.And the change of the magnetic domain in the process of magnetization is analyzed.The hysteresis characteristics of materials and the corresponding parameters of the magnetic properties of meaning are studied.A theoretical foundation was built for failure analysis of materials.And the design and working principle of the device was illustrated.Secondly,the ferromagnetic material nondestructive testing system was developed based on magnetomechanical effect technology.The system includes hardware detection system and software testing system.The hardware system is consists of three parts,including the design of magnetizing current source circuit,demagnetization circuit and magnetic sensor.The software testing system of the upper computer includes the design of the signal acquisition module,the data processing module,the database access module,the generating report module and the parameter display module.Finally,the magnetic hysteresis loop and magnetic property parameters of the sample were tested by the test system.The changes of the parameters such as coercive force,remanence and hysteresis loss were analyzed with the influence mechanism of stress on the magnetization process.The results show that the device can detect the stress changes inside the material sensitively.In addition,by measuring the change of magnetic property parameters before and after hydrogen corrosion,it is found that the hysteresis loop of the material is broadened and the coercive force abrupt after hydrogen corrosion,which indicates that the mechanical properties have changed.Thus the early damage prediction of ferromagnetic materials is realized.