Pipeline material detection method based on magnetic compression effect

JIN Xinjiu; YANG Lijian; GENG Hao

doi:10.7688/j.issn.1000-1646.2025.06.15

Abstract：[Objective]With the longer service life of oil and gas pipelines,the failure to identify the pipeline material due to data deficiency has become increasingly prominent.Traditional detection methods are unable to meet the engineering requirements for material identification and aging status assessment.A novel non-destructive testing method is expected to be proposed based on the magnetic compression effect.By analyzing the base value variation of magnetic flux leakage(MFL)signals in different steels under an applied external magnetic field,a correlation model between material and magnetic signal was established to provide a theoretical basis and technical approach for achieving rapid,accurate,and non-contact identification of pipeline materials.[Methods]The magnetic charge theory was integrated with the magnetic compression effect to develop a mathematical model describing the MFL field on the surface of steel under the influence of an external magnetic field.A theoretical derivation was performed to establish the functional relationship among the MFL signal base values,the external magnetic field intensity,and the material's magnetization intensity.The degree of the magnetic compression effect was proposed to be quantitatively characterized by the magnetic compression coefficient.Through the systematic experimental design,six representative structural and pipeline steels were selected as test materials,including Q235,Q345,X52,X65,X70,and X80.The specimens were machined into a standardized dimension of 270 mm × 140 mm × 10 mm.On a custom-built high-precision MFL testing platform,the external magnetic field was incrementally increased from 0 to 48 kA/m in steps of 1 kA/m,and the corresponding MFL signal base values were recorded in real time.To further validate the stability of the method,comparative tests were conducted between the signals obtained from original state steel plates and those obtained from polished plates with a surface roughness of 0.8 μm.All experiments were replicated to ensure both repeatability and accuracy of the results.[Results]According to the experimental results,with the enhancement of external magnetic field intensity,the MFL signal base values in all tested steel materials exhibit an initial increase followed by a subsequent decrease.The peak position varies significantly with the magnetic properties of the material.Specifically,the signal base values for Q235 and X65 peak at 24 kA/m,for X70 and X80 at 25 kA/m,while for Q345 and X52 with higher magnetization intensity,the peaks occur at 26 kA/m.This variation pattern highly coincides with the saturation magnetic characteristics of each steel's M-H curve,which indicates the close relation between the critical field strength for the onset of the magnetic compression effect and the material's magnetic properties.Furthermore,tests conducted under varying surface conditions of the steel plates reveal that,although the signal amplitudes differ,the critical point at which the base value begins to decline remains consistent for the same material.This finding confirms that the method is insensitive to surface conditions,with good anti-interference capability and adaptability to diverse operational environments.[Conclusions]A non-destructive testing method was proposed for pipeline material identification based on the magnetic compression effect.By establishing the correspondence between the MFL signal base values and the external magnetic field intensity,an effective differentiation between various structural and pipeline steels was achieved.This method exhibits not only good repeatability but also strong engineering applicability.The detection results are unaffected by complex factors such as internal pipeline surface roughness or corrosion state,making it suitable for complex working conditions such as internal pipeline detection.The research results provide a new technical means for material identification and safety assessment of aging pipelines,holding significant theoretical importance and engineering application value.