About Liquid Penetrant Testing
Liquid or dye penetrant testing (PT) is based on the infiltration of liquid penetrant into open surface discontinuities. Penetrant testing is not applicable on high porous materials. The dye penetrant method is used to determine surface defects, including surface cracks, pores, lack of fusion and inter-granular corrosion. Dye penetrant testing is performed on welds and parent material
A distinction should be made between dye penetrant testing and fluorescent penetrant testing, with only the near-surface area of a test piece being examined. After pre-cleaning, the penetrant is applied to the surface area of the test piece. This penetrates into fine cracks or pores through the capillary effect. After carefully removing the rest of the test medium from the surface, a developer is applied to pull the dye penetrant out of the pores and cracks, creating indications which can then be evaluated.
The dye penetrant test is usually performed with a red dye penetrant, which can be done in daylight. Whereas the fluorescent dye penetrant test uses a fluorescent test agent, which is much easier to evaluate in darkness or under UV light.
Liquid penetrant testing can be applied to any non-porous clean material, metallic or non-metallic, but is unsuitable for dirty or very rough surfaces. Surface cleaning is a vital part of the penetrant testing technique. The method can be manual, semi-automatic or fully automated. Penetrant inspections on continuous-operation production lines in which the specimens are cleaned, dipped, washed and dried on a time cycle are common.
Liquid Penetrant Testing – a six-stage process:
- Surface cleaning (degreasing etc.)
- Application of a penetrant liquid (dipping, spray, brush)
- Removal of excess penetrant (solvent, water)
- Application of developer
- Inspection of test surface (visual, television camera)
- Post-inspection cleaning (anti-corrosion solutions)
DEKRA offers solutions to fully automate the visual inspection stage of the process. The inspection can be performed by robotic handling of the specimen on a programmed procedure with inspection camera viewing and pattern recognition to identify and recognize flaws. This method is increasingly used in advanced mechanized applications.
DEKRA’s penetrant testing specialists are certified according to ISO 9712 and we meet the following testing standards: ISO 3452-1:2013, PNAE G-7-018-89, GOST 18442-80.