What is the difference between continuous and residual magnetization in MPT?

Continuous magnetization refers to the process wherein an external magnetic field is applied to a test object during the magnetic particle testing (MPT) procedure. This field allows ferromagnetic particles to align and form indications around any discontinuities present. The magnetization only lasts for the duration of the applied magnetic field; once the field is removed, the test object may retain some magnetic properties but is not considered continuously magnetized.

Residual magnetization, on the other hand, is the magnetization that remains in the material once the external magnetic field is removed. This residual magnetization can result from the behavior of the ferromagnetic material itself, allowing the material to hold onto some level of magnetism even after the inspection has concluded.

Understanding this distinction is crucial for interpreting results in magnetic particle testing, as the indications formed during the test are primarily dependent on the continuous magnetization applied during the inspection, while any residual magnetization could lead to misinterpretation of results or unwanted magnetic attraction post-inspection.