Principles of penetrant testing
Penetration testing is a non-destructive testing method based on the principle of capillary action of liquids and is used to detect open surface defects. 
Penetration Testing Applications
Material properties and defects relevant to penetrant testing:
- Penetration testing is suitable for detecting open surface defects in all materials except porous materials.
- For ferromagnetic materials, magnetic particle testing is the preferred method; Penetration testing is used only as an alternative or auxiliary method.
- For non-ferromagnetic materials, penetration testing is the preferred method for detecting surface defects.
Applicable material areas for penetrant testing:
The. Penetration testing is applicable to almost all product forming processes, including castings, forgings, welds, tubes and plates, especially for materials with complex shapes.
B. The types of materials suitable for penetrant testing are:
- Cast iron;
- Various carbon and alloy steels;
- Aluminum, magnesium, copper, titanium, zirconium, hafnium and other non-ferrous metals and their alloys;
- ceramics;
- Composites, plastics, etc.
Process of a penetration test
The penetrant testing process flow essentially includes pretreatment, penetrant application, removal of excess penetrant, imaging, and display of observation records.
The. Surface requirements for inspection:
- The surface to be tested must be free from rust, oxide film, welding spatter, iron filings, burrs and any protective layer that would affect the penetration test.
- To qualify, the surface appearance must be checked and the roughness must not be too large so as not to affect detection.
- When carrying out spot tests, the staging area around the test area must be enlarged by 25 mm.
B. Items to check:
- penetrating; imaging agents; Cleaning products; emulsifiers (if applicable);
- lighting equipment; illuminometers; Black light illuminator (if applicable); black light (if applicable);
- Thermometer;
- Test block.
Advantages and Limitations of Penetration Testing
| Advantages of Penetrant Testing | Limitations of Penetrant Testing |
| Short employee training times, fast entry | High work intensity and high demands on staff responsibility |
| Most methods have simple equipment | N/A |
| Suitable for almost all materials and different types of products (non-porous) | Only surface opening defects can be detected |
| Intuitive display; Simple process; Complete coverage at once | Slow detection speed |
| Suitable for different environments, no water or electricity | Heavy contamination |
Content requirements for penetration testing records and reports
- registration and report number;
- The standards and levels of inspection and acceptance execution;
- Detection object information: name, drawing number, part number, material, heat treatment status, detection location, detection proportion, surface condition, detection time, etc.;
- Testing equipment and devices (brand, model, number);
- The detection process parameters include penetration time, imaging time, penetrant application method, light intensity, pretreatment method, removal method, etc.
- Schematic representation of inspection;
- Test data evaluation results;
- testing personnel;
- Exam time and location.
