The magnetoscopy is a system of non-destructive investigation that is realized magnetizing a piece to examine evidencing the dispersed flow that is recorded in correspondence of the discontinuities that will bring out superficial and subcortical defects of every type:
A ferromagnetic material can be magnetized either by passing it through an electric current inside it, or by placing it inside a magnetic field originating from an external source. It can be magnetized the whole body or only a part of it, depending on the size of the material and the power of the instrument used.
To be detected, a break shall interrupt the normal path of the magnetic field lines. If the workpiece is homogeneous, parallel and uniform lines of magnetic flux will be determined in the workpiece, but when discontinuities occur, the presence of air, unable by its nature to sustain the same amount of magnetic field per unit volume of metal, causes an interruption of the flow that disperses to the outside of the piece.
In order to detect such anomalies of the path, the technique requires the use of ferromagnetic powder, to be evenly distributed on the surface of the body to be examined, which powders, once magnetized the body, will concentrate in the areas where the dispersed flow lines thicken, resulting in a small mound visible to the naked eye.