Research On Pipeline Stress Detection System Based On Coercivity

With the large-scale use of oil and gas pipelines in China,the operational safety of pipelines is more worthy of attention.At present,oil and gas pipelines are usually made of low-carbon steel and other ferromagnetic materials,the pipeline in the long-term practical operation of the project will not avoid the stress concentration area,the existence of stress concentration area will lead to rupture and corrosion pipeline defects,resulting in adverse consequences and Huge economic losses and safety of life and property.It is an important means to avoid the accident occurrence of the stress concentration area of the active pipeline.The magnetic parameters of ferromagnetic materials are affected by stress,in which coercivity and stress there is a certain relationship and the measurement is not easily affected by the outside world,the use of coercivity indirect measurement of stress,the pipeline stress detection is of great significance.This paper mainly studies the characteristics of ferromagnetic materials,magnetization process and other basic theory.Through the theoretical exploration and analysis of the coercivity of ferromagnetic materials,it is proved that the coercivity can measure the stress of the pipeline: the application of stress will hinder the irreversible magnetization phase in the magnetization process,and the coercivity is generated At this stage,the application of stress will have an effect on the ferromagnetic material.In this paper,a pipeline stress detection method based on coercivity is proposed,and the hardware and software system of pipeline stress detection based on coercivity is constructed.The system uses U-shaped probe to detect,which even wound a certain number of turns of the excitation coil and induction coil,the probe placed on the surface of the test object,the use of low-frequency sinusoidal signal through the power amplifier circuit access excitation coil U-type probe with the test Pieces of AC magnetization,the induction signal through the induction signal conditioning circuit to generate the induction pulse.After the main control chip receives the pulse signal,the excitation current value is collected through the coercive force acquisition circuit,and the coercivity value of the material is processed by the algorithm.Through the analysis of the coercivity value can be indirectly obtained by the stress level of the material,so as to carry out stress assessment.The experiment,the induction effect of U-shaped probe was analyzed by different frequencies,and the accuracy and stability of the system were tested.Q235 steel was used as the workpiece material to detect the coercivity at the elastic deformation stage.The linear relationship between the coercivity and the X70 pipeline is selected.The X70 pipeline low-carbon,X80 pipeline low-carbon steel as the material of the workpiece in the elastic deformation stage of the tensile test,the thickness of the stress-free Q235 steel workpiece to measure.The experimental results show that the U-shaped probe has the best magnetization at the frequency of 30Hz-50 Hz,the coercivity of the Q1235 and other materials in the thickness range of 6mm thickness.The error range of the system is ± 2%.The measurement accuracy is 0.1A/M;the standard deviation is1.92.The stress of the ferromagnetic material is linearly related to the measured coercivity value.The different pipe materials have some influence on the initial value of the coercive force,but it does not affect the linear relationship between the stress and the coercivity.The same thickness of the same material in 12 mm does not affect the coercivity value detected by the system device..