Dye Penetrant Inspection Colour Contrast

This technique is limited to surface inspection of a wide range of materials i.e. ferrous or non-ferrous, machined parts and weldments. High permeability / porous materials should not be inspected using DPI due to very high bleed out.

DPI Defect


  • Preclean the surface to be inspected using a solvent cleaning agent or water.
  • If water is used the surface must be dried.
  • Apply a dye to the surface and allow to penetrate any potential defects. The penetrant must not be allowed to dry for the duration of the dwell time.
  • Excess penetrant is then removed by a dry lint free cloth before and after removal using a moistened lint free cloth taking care not to contaminate the surface.
  • A contrasting developer is applied to the surface ensuring a thin even coverage. The developer acts as blotting agent and reverse capillary action draws the penetrant from the defect causing a bleed out.
  • The surface is then inspected under white light conditions of 1076 Lux or greater to detect any discontinuities or defects out with the specification desired by the client.
  • Report any findings for attention or issue a report which is acceptable to specifications.
  • After inspection is repeated the surface must be cleaned prior to shipping.

DPI Defect2



Services Sectors
Oil & Gas

Contact Details
Unit 22, E-Net Park
Mill Road Industrial Estate
West Lothian
EH49 7SF

TEL: 01506 844944


Opening Hours
Monday:           08:00 - 16:30
Tuesday:          08:00 - 16:30
Wednesday:     08:00 - 16:30
Thursday:         08:00 - 16:30
Friday:              08:00 - 13:30
Saturday:          Closed
Sunday:            Closed