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Ropax Ltd

Dye Penetrant Inspection (DPI) Services

Dye Penetrant Inspection (DPI) is a widely used technique for identifying surface breaking defects such as cracks, cold laps and porosity in all non-porous materials. Typical uses include the detection of fine defects in aircraft components and on non-ferrous welded parts including stainless steels, aluminium and duplex. Advantages of DPI are:

  • It is simple to carry out
  • It is a relatively inexpensive technique

DPI Theory

DPI is a method that is used to reveal discontinuities by 'bleed out' of a coloured or fluorescent dye from a discontinuity. The technique is based on the ability of a liquid to be drawn into a 'clean' surface-breaking defect by capillary action. After a period of time (known as the ‘dwell time’ - typically 20 minutes) excess surface penetrant is removed and a developer applied. This acts as a blotter and draws out the penetrant from the defect to reveal its presence.