Penetrating Liquids

The non-destructive liquid penetrant method is a test that helps determine surface damage on inspection parts. This method is used to detect surface-exposed discontinuities, defects or anomalies in metallic and non-metallic materials. Liquid penetrant inspection generally involves the following steps:

1. Cleaning and preparation of the material: The surface must be perfectly cleaned so that it is free of any contaminant such as grease or paint. Traces of rust must also be removed.
2. Application of the penetrant liquid: There are different ways to apply the penetrant liquid test, such as by immersion of the piece, spreading the liquid with a brush, pouring the liquid directly on the piece or by spraying. The objective is to completely cover the piece to obtain a thin and uniform film over the entire surface. When obtaining this film, a period known as “penetration time” must be waited, during which the liquid will enter the discontinuities.
3. Removal of excess penetrating liquid: In this phase we will proceed to remove the surface layer of the penetrating liquid. So that only what is stored in the discontinuities remains. This is the most important step of the process, since the result of the inspection will depend on its correct completion. Failure to correctly remove the penetrating liquid where there is no indication, as this may cause non-relevant indications to be evaluated.
4. Application of the developer: The developer is a white powder, which helps to contrast between the surface and the indication of the discontinuities, and also helps to extract the penetrant from them.

Liquid penetrant inspection is a very useful technique to detect discontinuities on the surface of the materials being examined, which may lead to future material failures.