Which statement about residual magnetizing inspection is true?

Which statement about residual magnetizing inspection is true?

• A. Subsurface discontinuities are readily apparent
• B. It is used in practically all circular and longitudinal magnetizing procedures
• C. It may be used with all steels which have been heat treated for stressed applications
• D. It cannot detect surface cracks

Answer: (C)

Residual magnetizing inspection relies on the magnetization that remains in a ferromagnetic part after the external field is removed. The leftover (remanent) field concentrates around flaws that interrupt the magnetic circuit, so magnetic particles gathering at those leakage fields reveal crack-like indications on the surface or just beneath it. This approach is particularly suitable for steels that have been heat treated for stressed applications because such components are designed to withstand high loads and are commonly inspected for cracks that could grow under service; their ferromagnetic nature and the presence of residual stresses make the residual field useful for exposing surface-breaking defects. Subsurface discontinuities aren’t typically revealed as clearly with this method, so they aren’t described as readily apparent. It isn’t claimed to be used in virtually all circular and longitudinal magnetizing procedures, since residual magnetizing is one of several inspection approaches and isn’t universally applicable in every scenario. And indeed, surface cracks can be detected with this method, so saying it cannot detect surface cracks isn’t accurate.

Residual magnetizing inspection relies on the magnetization that remains in a ferromagnetic part after the external field is removed. The leftover (remanent) field concentrates around flaws that interrupt the magnetic circuit, so magnetic particles gathering at those leakage fields reveal crack-like indications on the surface or just beneath it. This approach is particularly suitable for steels that have been heat treated for stressed applications because such components are designed to withstand high loads and are commonly inspected for cracks that could grow under service; their ferromagnetic nature and the presence of residual stresses make the residual field useful for exposing surface-breaking defects.

Subsurface discontinuities aren’t typically revealed as clearly with this method, so they aren’t described as readily apparent. It isn’t claimed to be used in virtually all circular and longitudinal magnetizing procedures, since residual magnetizing is one of several inspection approaches and isn’t universally applicable in every scenario. And indeed, surface cracks can be detected with this method, so saying it cannot detect surface cracks isn’t accurate.