For an effective low cost inspection, Liquid Dye Penetrant Inspection (DPI) is a widely used technique for locating cracks in all non-porous materials such as metals and plastics.
It is particularly suitable for non-ferrous, forged, cast or welded products which are prone to cracking.
- A visible or fluorescent dye, either solvent or water-based, is applied to the surface or the item by immersion or spray
- The dye penetrates any cracks through capillary action (known as the dwell time) and is usually left for a minimum of 20 minutes
- Excess dye is then removed with lint-free cloth leaving none visible to the naked eye
- A developing agent is applied, which, using reverse capillary action, quickly and clearly reveals crack lines.
Dye Penetrant Inspection is suitable for components of any size.
- Section of material with crack not visible to the naked eye
- Dye is applied to the surface
- Excess dye is removed
- Developer is applied, making the crack visible.
Dye penetrants are classified by sensitivity levels. Visible penetrants are typically red or blue in color, and represent the lowest sensitivity. Fluorescent penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) radiation (also known as black light). Since fluorescent penetrant inspection is performed in a darkened environment, and the excited dyes emit brilliant yellow-green light that contrasts strongly against the dark background, this material is more sensitive to defects.
When selecting a sensitivity level, many factors must be considered, including the environment under which the test will be performed, surface finish of the specimen, and size of defects sought. This technique can be quite portable because, in its simplest form, the inspection requires only 3 aerosol spray cans, lint free cloths, and adequate visible light.
Advantages and disadvantages
The main advantages of DPI are the speed of the test and the low cost.
Disadvantages include the detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean surface where excessive penetrant can be removed prior to being developed and it will not work on painted or rough surfaces.
See a complete range of the standards used by ITCL for Dye Penetrant Testing – here
Here at ITCL we pride ourselves on the high quality of application and testing by our experienced technicians. Our workforce is fully qualified to current standards and work to approved procedures and control checks. Environmental and health & safety issues are of paramount concern to all staff working on your site, with expert consultation always available.
ITCL offers a comprehensive 24hr in-house and on-site service.
Contact a member of the ITCL team on 0151 356 7118 for more information.
Below is a selection of standards used by ITCL for Dye Penetrant Inspection
- ISO 3059, Non-destructive testing – Penetration testing and magnetic particle testing – Viewing conditions
- 3452-1, Non-destructive testing. Penetrant testing. Part 1. General principles
- ISO 3452-2, Non-destructive testing – Penetrant testing – Part 2: Testing of penetrant materials ISO 3452-3, Non-destructive testing – Penetrant testing – Part 3: Reference test blocks
- ISO 3452-4, Non-destructive testing – Penetrant testing – Part 4: Equipment ISO 3452-5, Non-destructive testing – Penetrant testing – Part 5: Penetrant testing at temperatures higher than 50 °C
- ISO 3452-6, Non-destructive testing – Penetrant testing – Part 6: Penetrant testing at temperatures lower than 10 °C ISO 12706, Non-destructive testing – Penetrant testing – Vocabulary
- ISO 23277, Non-destructive testing of welds – Penetrant testing of welds – Acceptance levels
- EN 571-1, Non-destructive testing – Penetrant testing – Part 1: General principles. May be replaced by EN ISO 3452-1
- 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 US Standards ASTM E 165, Standard Practice for Liquid Penetrant Examination for General Industry ASTM
- E 1417, Standard Practice for Liquid Penetrant Testing 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)