The non-destructive test by means of penetrating liquids is a type of test that allows to check the integrity of a sample and to detect the presence of surface defects thanks to the application of a particular type of liquid that can penetrate inside the discontinuities.

Penetrating liquid testing uses the method of capillarity, i.e., the ability of a liquid to rise inside a capillary tube, and the physical characteristics of liquids such as viscosity and surface tension. Penetrating ability is a very important requirement that defines the sensitivity of the test.

The test can be performed by two types of methods: the colour contrast method and the fluorescent liquid method

The inspection with penetrating liquids is a particularly suitable method to highlight and locate surface discontinuities, such as cracks, porosity, folds, in a fast and economic way and with great accuracy.