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Dye Penetrant Inspection (DPI) – Liquid Penetrant Inspection (LPI) – Liquid Penetrant Testing (PT)

ECE Global Inspection Services offers a complete line of surface examination techniques including Liquid Penetrant and Magnetic Particle NDT applications and techniques. The application of these testing methods by experienced technicians has been proven to give reliable information as to the shape and length of different defects that are open to surface.

This can be very important when indications are noted and additional resources and techniques are needed to assess the overall condition of your component (e.g. Phased Array Ultrasonic Testing).

Many of the technicians employed by ECE Global are multi-disciplined and able to apply the other NDT disciplines that may be necessary to fully determine the suitability of the component for service.


Dye Penetrant Inspection (DPI), also called Liquid Penetrant Inspection (LPI) or Liquid Penetrant Testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). For applications where a greater sensitivity to smaller defects is required, the fluorescent penetrant method is preferred.

The Penetrant may be applied to all non-ferrous materials and ferrous materials, but for inspection of ferrous components magnetic-particle inspection may be preferred for its subsurface detection capability.

Commonly, DPI is used to detect cracks, surface porosity, lack of penetration in welds and defects resulting from in-service conditions (e.g. fatigue cracks of components or welds) in castings, forgings, and welding surface defects.


Penetrant Testing


1. Section with a normally not visible surface-breaking crack.

2. Penetrant is applied to the surface.

3. Excess Penetrant is removed.

4. Developer is applied, rendering the crack visible.



The effectiveness of this method relies on many factors including the training/skill of the technician, how clean the part is, and the procedure that is being used to perform the test. DPI is a relatively cost effective method, considering the amount of training required, and the cost of materials used. DPI can be used in both manufacturing and in-service inspections. As with other inspection methods, DPI requires that a known defect standard has been defined using standard parameters. Thus indications can be compared to with defined allowable limits.

The basic steps are:

  1. Clean the part 
  2. Apply the Penetrant and allow dwelling
  3. Remove excess Penetrant.
  4. Apply a developer and allow developing
  5. Read the part for indications. 6) Clean the part.

This may sound easy, BUT, here comes the tricky part. There are several variations to every step – i.e. what type of Penetrant? What method (of excess Penetrant removal) of Penetrant? What sensitivity of Penetrant? What form of developer? What class of solvent (to remove excess Penetrant)?

Our experienced technicians and staff NDE Level III will provide the best answers to these important questions.


Often Referenced Standards:

ASTM International (ASTM)

  • ASTM E 165, Standard Practice for Liquid Penetrant Examination for General Industry
  • ASTM E 1417, Standard Practice for Liquid Penetrant Testing

American Society of Mechanical Engineers (ASME)

  • ASME Boiler and Pressure Vessel Code, Section V, Art. 6, Liquid Penetrant Examination
  • ASME Boiler and Pressure Vessel Code, Section V, Art. 24 Standard Test Method for Liquid Penetrant Examination SE-165 (identical with ASTM E-165)

European Committee for Standardization (CEN)

  • EN 571-1, Non-destructive testing – Penetrant testing – Part 1: General principles
  • EN 1371-1, Founding – Liquid penetrant inspection – Part 1: Sand, gravity die and low pressure die castings
  • EN 1371-2, Founding – Liquid penetrant inspection – Part 2: Investment castings
  • EN 2002-16, Aerospace series – Metallic materials; test methods – Part 16: Non-destructive testing, penetrant testing
  • EN 10228-2, Non-destructive testing of steel forgings – Part 2: Penetrant testing
  • EN 10246-11, Non-destructive testing of steel tubes – Part 11: Liquid penetrant testing of seamless and welded steel tubes for the detection of surface imperfections
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