Liquid penetrant inspection
In practice liquid penetrant inspection is usually only applied on non-ferro materials such as aluminium, but it could also be applied on ferro materials and non-metals. Liquid penetrant inspection is only suitable to find surface discontinuities which have an open connection with the surface. A disadvantage of liquid penetrant inspection is that this method of non-destructive research is quite a slow technique compared to other methods, because of the penetration time and drying time.
The penetrant method is based on the physical phenomenon of ‘’capillary action”. The red penetrant fluid is distributed across the clean surface and will enter the openings in the material. After the penetration time has expired, the superfluous penetrant will be removed with cloths and a cleaner. The next step in the process is that a developing agent is applied on the surface, so that any discontinuities will be visible after some time. On the basis of the acceptance criteria it will be assessed whether it concerns a relevant indication or not.