Damage Testing Of The Metal Pipeline Based On Metal Magnetic Memory And Research On Evaluation Methed

The pipeline is a main tool of transportation for our country’s energy. But the corrosion, perforation, fracture of pipeline cause a great deal of security problems. It is a task of top priority to take safety assessment on a regular basis for underground pipeline and to prevent accident happen. However, The traditional non-destructive testing(NDT) request the pipeline either smooth surface or the magnetization device, such as ultrasonic testing and magnetic flux leakage(MFL) testing. They can’t meet the new requirements of the new situation. As a result, with its simplicity, non-contact and unexpected, the metal magnetic memory(MMM) NDT technology is born at the right moment. This paper mainly studied by the following several aspects:First of all, the paper analyzes magnetic properties of the ferromagnetic material in the condition of elastoplastic deformation and fracture. The JilesAtherton model is introduced into elastic stage to reflect the changing rule of effective field which has magnetostrictive change with the stress change. The modified J-A model based on the theory of dislocation is used in plastic stage and four factors which can cause the change of the magnetization is considered: mass multiplication of dislocation, magnetoplastic energy, residual stress energy and demagnetizing energy. And effective field model of plastic deformation is established. Pull the pinning coefficient and interdomain coupling coefficient have influences on the plastic strain; In fracture stage, materials have a peak-topeak saltation in magnetization. The magnetic dipole model are established to simulate the mutation.Then with Q235 ferromagnetic pipeline as the research object, the threedimensional model is established and the magnetic characteristic of it is analyzed by the finite element method. The change rule of magnetic signals in elastic stage, plastic stage and fault stage is studied. It shown that magnetization mutation in fault stage is greater than in elastic-plastic stage. Based on different magnetic signal characteristics in different deformation stages, the influence of shape defects, defect diameter, lift-off valve and the orientation of defects on the magnetic signal is studied futher. It is found that defect shape and diameter affect the size of the magnetic signal mainly by changing the magnetic leakage area, mutation signal enhanced with the increase of magnetic leakage area. Liftoff valve and orientation of defects defects are mainly affected by radiation distance and orientation, away from the source of radiation, magnetic signal weakened. The paper explored corresponding magnetic signal evaluation parameters, then established the quantitative relationship between defect features and characteristics of the magnetic signal.Next, the sensor module of MMM testing equipment is developed including the choice of sensors, host module and peripheral devices. The improved adaptive wavelet threshold de-noising method is put forward to reduce the magnetic signal noise. Again, samples’ s model is trained by BP neural network. A matlab GUI is established and the MMM quantitative evaluation system is got. Finally, the paper make the function that can intelligently evaluate defect number, defect depth and defect types come true.