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Liquid penetrant Testing (PT)

Liquid penetrant Testing (PT)

Non-Destructive Inspection (NDT) is used to detect any surface defects present on different types of materials, such as castings, welds, pipes, and so on.
Specifically, the liquid penetrant testing method is based on visual observation of the surface after sequential application of a penetrant product and a detector.


Of the Method with Penetrating Liquids

The liquid penetrant method is used in various industries to detect surface discontinuities on components.

In the field of welding components under pressure in the chemical, petrochemical and energy industries, this method offers greater sensitivity than traditional visual inspection, allowing the success of a weld bead to be identified with precision.

In the field of plastics and composites, the liquid penetrant method is an effective alternative to magnetoscopic and eddy current methods for detecting surface discontinuities.

In the aviation industry, the liquid penetrant method is used with high-sensitivity products to detect even the smallest cracks on aircraft components subjected to fatigue or thermal stresses.

In the automotive and motor industry in general, the automation of the control with penetrating liquids allows to associate the high productivity with a higher and constant quality of the components of motor vehicles, turbines and other products.


Of the Method with Penetrating Liquids

Among the ADVANTAGES of nondestructive testing with liquid penetrants the most important are:

  • Theapplicability on all materials, metallic and non-metallic;
  • The wide applicability, independent of the geometry of the parts to be examined;
  • The highlighting of outcropping discontinuities in surfaces, even very small ones;
  • A fair speed in the application of the process.

The method never allows the detection of sub-surface discontinuities, nor discontinuities surfaced on the surface but with traces of contaminants such as: paints, fats and oils, oxides, liquids, etc.
For this last reason, in the application process, the surface preparation stage is very important, which consists, essentially, of its thorough cleaning.

The method does not allow, for obvious reasons, the control of very porous materials.

In Control with Penetrating Liquids

Two products are always required for the application of the process: the PENETRATING LIQUID and the DETECTOR.
Depending on the method of penetrant removal, the following may also be required: emulsifier or solvent remover

It is that liquid which, with its penetration characteristics resulting from the three properties, surface tension, wetting power and viscosity, is capable of penetrating even very small discontinuities.

The colored trace that is created as soon as the application process is completed highlights the geometry of the discontinuity itself.

Penetrating liquids are mixtures generally consisting of a base product made up of petroleum or light oils from aromatic and aliphatic hydrocarbons, modified with specific additives so as to increase the flash point, and colored or fluorescent pigments.

Depending on color, penetrants are divided into:

  • COLOR CONTRAST: Usually red in color, they contain colored pigments visible in natural light. Defect detection is by color contrast between penetrant and detector blank.
  • FLUORESCENTS: yellow in color, they contain fluorescent pigments visible on inspection only by exciting their fluorescence with special Idi Wood or ultra violet black light lamps), in a darkened environment.
  • COLOR CONTRAST FLUORESCENTS: usually reddish in color, they are a special mixture of the two types of penetrants described above.

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