Magnetic Particle Testing
Dry Powder Method
Dry Powder is an inexpensive and very portable method of NDT. It is suitable for detecting surface discontinuities. Used where portability of test method is important. This method is typically used on miscellaneous parts and large surface areas and best for examining rough surfaces
The limitations of this method are that the surface must be clean and dry and the yoke must be repositioned systematically to ensure that randomly oriented discontinuities are detected and are difficult on parts with complex geometry or with a coating.
Black on White Wet Method
This method is portable and good for detecting near-surface type discontinuities. It is used for the inspection of localized areas on miscellaneous parts and large surface areas. Black on White, wet method is a more sensitive method then the dry method.
The limitations of this method are similar to that of dry powder, the part must be clean and dry, and the yoke must be repositioned systematically to ensure that randomly oriented discontinuities are detected. This method is also may not be effective on parts with complex geometry.
The most significant limitation to this method is that the penetrant material and the surface of the item to be used at temperatures between 15C and 50C
The fluorescent method can only be used where lighting can be controlled and also only for near-surface type discontinuities. Like the other methods, it is used for localized areas on miscellaneous parts and large surface areas. The fluorescent method is the most sensitive of the three MT methods and used for critical components.
Fluorescent MT has the same limitations as both Dry and Wet Black on White, with the addition of requiring a dark area in which to work.
Note: in large manufacturing/aerospace a “wet bench” would be utilized for both MT and PT.
Until next week,