The pressure pipeline in line inspection technology is the most effective nondestructive testing method to detect the quality of buried oil and gas pipelines at present. In line inspection tool usually uses magnetic flux leakage (MFL) technology to detect the change of leakage magnetic field to detect pipeline defects. Permanent magnets magnetize the wall of the pipeline as an excitation. During the detection process, the magnetic field performance of permanent magnets is required to be high. At the same time, the magnetic performance of the permanent magnet in the magnetic cleaning pipe also determine the cleaning effect inside the pipeline. In this paper, the magnetic distribution of permanent magnets is studied and the Nd-Fe-B permanent magnets with the best magnetic properties are taken as the objects. The finite element simulation is used to optimize the shape of the permanent magnets with better magnetic distribution, and the magnetic intensity factors of the preferred cylindrical permanent magnets are analyzed. In addition, three experiments of the influence of temperature, the influence of the ferromagnetic combination, and the influence of the environment medium are conducted.

As a result, the relationship between the magnetic intensity of the Nd-Fe-B permanent magnets and the factors is obtained. The conclusion is of great significance to the design and research of permanent magnetic circuit in line inspection magnetization device.

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