Penetrant testing
The penetrant test (according to DIN EN ISO 3452-1, formerly DIN EN 571-1: penetrant test, general principles) is a non-destructive material test in which the capillary forces of fine surface cracks and pores are used to make them visible. A distinction is made between the dye penetrant test and the fluorescent penetrant test.
Dye penetrant test (in daylight,> 500 lux)
In the dye penetrant test (PT), the surface of the component to be tested is freed of grease and oil residues. A dye penetrant (contrast) is then applied. This can be done by applying with a brush, by dipping in a bath, or, in well-ventilated places, by spraying on. "Forced wetting" occurs through the application methods mentioned. The penetrant has a high creeping capacity , uses the capillary effect of the finest gaps and has a strong color contrast to the developer .
After the exposure time, which depends on the material to be tested, the surface is cleaned with water or a special cleaner, dried and the developer is applied. The developer is a fine-grain powder, usually based on lime - chalk , suspended in water or solvent - which locally absorbs the penetrant remaining in fine cracks (pores) through the capillary action of its cavities (suction). As a rule, the penetrant is a red dye solution and the developer is white. The large color contrast makes it possible to easily localize defects and determine the course of cracks.
Fluorescent penetrant test (in the dark, <20 lux)
When the ambient light is low, you can work with a fluorescent penetrant, which is made visible with the help of UV radiation. This test is much more sensitive than the dye penetrant test because the fluorescent particles create a luminance contrast by converting the UVA radiation into visible light. The human eye reacts to luminance contrasts much more sensitively than to color contrasts. The main areas of application for fluorescent penetrant testing are the automotive, aerospace industries.
Sources of excitation for fluorescent testing
According to EN ISO 3059, a standard-compliant fluorescent test must use a UV-A radiation source or a blue light for fluorescence excitation. While discharge lamps (mercury vapor, xenon or metal halide lamps) have been used exclusively in the last few decades, UV-A LED lamps or blue light lamps are primarily used today. Blue light (450 nm) is regulated and approved in DIN CEN / TR 16638 from May 2014.
UV radiation can endanger the eyes. U. protective measures necessary.
The penetrant test can be used on all materials that allow a clear indication of surface defects (are not porous ), mainly on metals, plastics (with restrictions, e.g. Teflon), glazed ceramics and the like. In the case of machine parts made of steel , a solvent-based developer is usually used due to the high susceptibility to corrosion by water, or the magnetic particle test is used for ferromagnetic (non- austenitic ) steels .
The dye penetrant test is suitable for quickly finding cracks (up to a thousandth of a millimeter wide) in the surface of a material. However, so-called false displays can occur on rough or brittle surfaces. These ads are not flaws. The method also does not allow any statement to be made about the depth of the flaw (depth of the crack) in relation to the display intensity: for example, a light pink colored display does not necessarily indicate a less deep crack than a deep red display. This partial lack of sensitivity has meant that this method is no longer approved as a test method, for example in the context of tests in general aviation.
Penetrant Testing Standards
General
Penetration tests, especially in the aerospace industry, are not carried out according to the originally German DIN EN ISO 3452, but primarily according to the American ASTM E 1417, which is now very similar to ISO 3452-2. Only products that are listed in the QPL (qualified products list) of the AMS 2644 and are therefore approved may be used for testing in accordance with this standard. The main differences are the ISO classification of the sensitivity of dye penetrants and the consideration and approval of fluorescent dye penetrants.
Norms
- DIN 25435-2, Recurring tests of the components of the primary circuit of light water reactors - Part 2: Magnetic particle and penetrant test
- DIN EN 1371-1, Foundry - Penetrant testing - Part 1: Sand, gravity and low pressure die castings
- DIN EN 1371-2, Foundry - Penetrant testing - Part 2: Investment castings
- DIN EN 2002-16, Aerospace - Metallic materials; Test methods - Part 16: Non-destructive testing, liquid penetrant testing
- DIN EN 10228-2, Non-destructive testing of steel forgings - Part 2: Liquid penetrant testing
- DIN EN ISO 10893-4 Non-destructive testing of steel pipes - Part 4: Penetration testing of seamless and welded steel pipes for the detection of surface imperfections
- DIN EN ISO 3059, non- destructive testing - penetrant testing and magnetic particle testing - viewing conditions
- DIN EN ISO 3452-1, Non-destructive testing - Liquid penetrant testing - Part 1: General principles
- DIN EN ISO 3452-2, Non-destructive testing - Penetrant testing - Part 2: Testing of penetrant testing media
- DIN EN ISO 3452-3, Non-destructive testing - Penetrant testing - Part 3: Control bodies
- DIN EN ISO 3452-4, Non-destructive testing - Liquid penetrant testing - Part 4: Devices
- DIN EN ISO 3452-5, Non-destructive testing - Liquid penetrant testing - Part 5: Liquid penetrant testing at temperatures above 50 ° C
- DIN EN ISO 3452-6, Non-destructive testing - Liquid penetrant testing - Part 6: Liquid penetrant testing at temperatures below 10 ° C
- DIN EN ISO 12706, non- destructive testing - liquid penetrant testing - terms
- DIN EN ISO 23277, Non-destructive testing of welded joints - Penetration testing of welded joints - Permissible limits
- DIN CEN / TR 16638, non- destructive testing - penetrant testing and magnetic particle testing using blue light
- ASTM International (ASTM)
- ASTM E 165, Standard Practice for Liquid Penetrant Examination for General Industry
- ASTM E 1417, Standard Practice for Liquid Penetrant Testing