Magnetic Memory Signal Characterization And Detection Analysis Of Defects In Pressure Equipment And Pipelines

The evaluation and judgment of the safety and reliability of pressure equipment and pipeline is related to the development of national economy and people’s life safety.If there are defects in the weld structure of the pressure equipment and pipeline,it is very easy to cause failure and destruction of the components.Conventional non-destructive testing methods can only detect macro defects such as cracks,pores and pits under shutdown conditions,but have limitations in detecting buried defects and stress concentration.Metal magnetic memory(MMM)testing technology is an emerging non-destructive testing technology based on electromagnetic non-destructive testing theory.It is the only non-destructive testing technology that can detect stress concentration at present.However,due to the lack of detection standards and evaluation standards,further theoretical and experimental research is needed.In this paper,the metal magnetic memory detection technology is applied to the flat plate and pressure pipeline structure with buried defects.Through the combination of ANSYS finite element simulation and experimental research,the change law of magnetic memory signal at the location of defects in different cases is extracted,and its characteristic parameters are analyzed quantitatively,which provides a theoretical basis for practical engineering application.In this paper,the plate,pressure equipment and pipeline with prefabricated defects are taken as the research object,and the pressure equipment structure is simplified to plate structure.The finite element simulation experiments of plate specimen under uniaxial and biaxial tensile loading are designed to analyze the pressure equipment under different loads.The finite element simulation experiment of internal pressure loading is designed.The changes of magnetic memory signal under different loading methods,different loads,different defect types and defect parameters are analyzed,and the magnetic memory characteristic parameters indicating the degree of stress concentration are extracted.The corresponding relationship between magnetic memory characteristic parameters and load and defect parameters is analyzed quantitatively.The finite element simulation results are further verified through the magnetic memory test of the plate specimen with defects under uniaxial tension and the magnetic memory test of the pipeline weld.The variation law of the magnetic memory signal of the pressure equipment weld defects is analyzed,and the characterization relationship of the characteristic parameters of the magnetic memory signal to the defects is obtained.The numerical simulation results show that the maximum value of normal gradient of MMM signal increases with the increase of defect depth and load.When the load is fixed,the increasing rate of the extreme value of the normal gradient increases with the decrease of the buried depth of the defect.When the depth of the defect is fixed,the increasing rate of the extreme value of the normal gradient decreases with the increase of the load.Then,in the simulation of uniaxial tension of cracked plate and internal pressure loading of cracked pipeline,the maximum points of normal gradient curve merge during the process of buried crack extending to the depth of 40% of the specimen thickness.The fitting curve between the extreme value of normal gradient and the load obtained from the magnetic memory test of a plate with a crack depth of 3mm under different tensile loads is the same as that obtained from the finite element simulation,which verifies the accuracy of the finite element simulation results.The magnetic memory test results of the pipeline with buried pores show that the extreme value of the normal magnetic field gradient near the hole with a diameter of 2mm is about twice that of the hole with a diameter of 1mm.Finally,through the field test results of pressure equipment,it is found that magnetic memory detection can not only effectively characterize the known defects,but also predict the crack growth trend by the distribution of normal gradient value of crack tip.The research of this paper realizes the organic combination of magnetic memory testing in three aspects: finite element simulation,testing experiment and engineering application.The characteristic parameters of magnetic memory signal,defect parameters and loading results are analyzed quantitatively.The research results provide technical support for the application of metal magnetic memory testing technology in pressure equipment and pipeline testing.