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Magnetic flux leakage (TFI or Transverse Field Inspection technology) is a magnetic method of nondestructive testing to detect corrosion and pitting in steel structures, for instance: pipelines and storage tanks. The basic principle is that the magnetic field "leaks" from the steel at areas where there is corrosion or missing metal.
Indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source. The presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak, since air cannot support as much magnetic field per unit volume as metals. To identify a leak ...
The field travels outwards from the exciter coil, through the pipe wall, and along the pipe. The detector is placed inside the pipe two to three pipe diameters away from the exciter and detects the magnetic field that has travelled back in from the outside of the pipe wall (for a total of two through-wall transits).
In this technique, permeability variations are suppressed by applying a magnetic field. The saturation probes contain conventional eddy current coils and magnets. This inspection is used on partially ferromagnetic materials such as nickel alloys, duplex alloys, and thin-ferromagnetic materials such as ferritic chromium molybdenum stainless steel.
Magnetic particle inspection (MT or MPI) is a form of MFL where small magnetic particles in the form of a powder or liquid are sprayed on the magnetized steel test object and gather at surface-breaking cracks. Alternating current field measurement (ACFM) is similar to eddy current applied to steel. Its most common application is to detect and ...
Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). The magnetic moment induced by the applied field is linear in the field strength, and it is rather weak. It typically requires a sensitive analytical balance to detect the ...
Magnetic field-assisted finishing, sometimes called magnetic abrasive finishing, is a surface finishing technique in which a magnetic field is used to force abrasive particles against the target surface. [1] As such, finishing of conventionally inaccessible surfaces (e.g., the inside surface of a long curved pipe) is possible.
However, the magnetic domains in a material are not fixed in place; they are simply regions where the spins of the electrons have aligned spontaneously due to their magnetic fields, and thus can be altered by an external magnetic field. If a strong-enough external magnetic field is applied to the material, the domain walls will move via a ...