Permanent magnet structure-based pipeline demagnetization device and application thereof

A pipeline demagnetization device based on a permanent magnet structure includes a central piece and permanent magnets distributed on the central piece. A magnetic field with alternating directions is formed in a wall of a pipeline in an axial direction from front to back, and strength of the magnetic field gradually decreases. The pipeline demagnetization device can be applied to the pipeline demagnetization using a built-in structure or an externally-built structure. The pipeline demagnetization device spatially constructs a set of stable alternately-decayed magnetic fields, so that the wall of the pipeline experiences the set of alternately-decayed magnetic fields when the pipeline that is magnetized spatially displaces relative to the set of alternately-decayed magnetic fields, thereby realizing demagnetization.