What is the term for an inspection method where an initial magnetizing force is applied and then reduced to a lower continuous value?

The term that describes an inspection method where an initial magnetizing force is applied and then reduced to a lower continuous value is the residual method. In this context, after the initial magnetization, the magnetic field strength decreases but the residual magnetism remains, allowing for defect detection through the observation of magnetic particles.

This technique is particularly useful in identifying subsurface defects and cracks in ferromagnetic materials. By applying a strong initial magnetization followed by a reduction, the residual magnetic field still holds enough strength to attract magnetic particles to any surface discontinuities. This creates a clear indication of defects even once the initial application of magnetization has concluded.

The surge method involves a rapid application of magnetization but does not focus on maintaining a lower continuous value afterward; the alternating method constantly changes the direction of the magnetic field; and the continuous magnetization method maintains the magnetic field at a constant level without initial surging. Each of these methods serves different purposes in magnetic particle testing and is characterized by varying techniques of magnetization.