Dye / fluorescent penetrants (PT)

Principle of the method
This non-destructive test exploits the capability of some fluids of penetrating inside surface defects (cracks, cavities, etc) by capillarity and not by gravity.

The low surface tension and the good wettability of these fluids ensure their penetration inside the thinnest irregularities. After the fluid application and penetration (the fluid is thus called “penetrant”) requiring a variable time depending on the kind of product used, of material to be inspected and of irregularity to find out, the excess of penetrating fluid is removed from the surface by running cold water.
Since water has a higher surface tension and a worse wettability than the penetrant, this is not removed from the cracks in which it is penetrated by capillarity. After washing - once again exploiting the capillarity principle - the penetrating fluid still inside the defect is extracted; to do this, a properly thick layer of white powder (detector) is laid on the piece surface. The penetrating fluid “comes up” and leaves in the detector a signal bigger than the defect generating it. Depending on the technique used, the defect can be highlighted in different ways: as a red or fluorescent spot that can be easily detected by irradiation with Wood’s light, in the dark. This method involves some difficulties in the defect evaluation as well: sometimes, mechanical machinings give some defect “indications” that can be solved by a particularly experienced operator, only.

Application
The inspection by penetrating fluids is a method particularly suitable for highlighting and locating surface irregularities such as cracks, porosity and pinching, in a rapid, cheap and accurate way. Contrary to magnetic checks, penetrating fluids can be successfully applied to any component, irrespective of the component geometry or material (except for porous pieces, e.g. sintered pieces, cast iron or pieces with very rough surfaces). To carry out this test, TEC Eurolab S.r.l. has a tank bank ideal for checking aluminium and titanium pieces. The check at the customers’ is carried out by means of aerosol bombs. 
Dye / fluorescent penetrants (PT)
Dye / fluorescent penetrants (PT)
Dye / fluorescent penetrants (PT)
Dye / fluorescent penetrants (PT)
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