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Ferromagnetic pipelines provide a major means for the conveyance of oil and natural gas. The self-magnetic leakage field (SMLF) generated by ferromagnetic pipelines has therefore attracted considerable attention in the field of pipeline examination and defect detection. This paper has the objective of analysing the magnetomechanical effect, which can be observed in the geomagnetic field, by establishing a mathematical model of the SMLF based on the theory of magnetic dipoles and the magnetomechanical effect, and to discuss the influence of factors such as the outer diameter, the geomagnetic field intensity, the operating pressure, etc. The results show that the length of oil and gas pipelines can be considered as infinite for the calculation of the SMLF. In addition, both the total flux density and the gradient modulus of the SMLF are shown to reach their maximum values above the pipeline. The parameter analysis indicates that the pipeline diameter and the height of the covering soil are two crucial factors in determining the SMLF. Finally, in an experiment to test the model, the error between the theoretical calculation and the actual measurement was 4.6%. Therefore, the model proposed in this paper can provide technical support for the calculation of the SMLF induced by pipelines, which has significance for the inspection of pipeline locations and pipeline defects. [ABSTRACT FROM AUTHOR]

Non-contact pipeline magnetic testing (NPMT) is a novel and non-destructive technology based on the metal magnetic memory (MMM) method, which can detect pipeline defects under trenchless conditions. There is a peak on the gradient modulus of the ground leakage magnetic field (GLMF), which is a signal characteristic of a defect. In this study, the physical principles of this technology were first discussed. Next, a spatial distribution model of the GLMF was built based on the theories of magnetic charge and magnetic dipole, which indicates the quantitative relationship between the defect and GLMF. The effects of the model parameter values on the gradient modulus were also discussed. The reliability of the model was verified by comparing the field testing signal with the model calculated value. Directions of further research are formulated, including factors affecting the model accuracy and the classification of defects. [ABSTRACT FROM AUTHOR]