Example radiograph showing different components of an assembly.
Radiography uses penetrating radiation directed towards a sample that attenuates the radiation through changes in either density or thickness. The penetrating radiation used in radiography is a higher energy (shorter wavelength) version of the electromagnetic waves that make up normal light. Visible light is in the same family as x-rays and gamma rays; however, in contrast to visible light, these higher energy rays can significantly penetrate into materials. Radiography may employ X-rays or gamma rays. X-rays are produced with electrical tubes that may be shut off, while gamma rays are produced by radioactive materials that must be shielded for safety when not in use.
As the radiation penetrates the specimen, the sample material stops a percentage of the incident amount from reaching the detector. The energy of the radiation affects its penetrating power, while density and thickness of the material governs its stopping power.
The detector used in radiographic inspection may be film or a digital medium; the images on these detectors will be negatives of one another. While both types have pros and cons, a significant capability of using digital detectors is that a sample can be moved around and viewed in real time.
Example of fluorescent magnetic particle inspection using UV light, with indications highlighted.
Advantages of Radiographic Inspection
- Technique is not limited by material type
- Can inspect assembled components intact (like a full suitcase)
- Minimum surface preparation required
- Tests the full thickness at once
- Sensitive to changes in thickness and density
- A permanent record of the result is obtained
Limitations of Radiographic Inspection
- Many safety precautions for the use of high intensity radiation
- Orientation between incident x-ray and flaw is critical
- Many hours of technician training prior to use
- Access to both sides of sample required
- Determining flaw depth is impossible without additional angled exposures
- Expensive initial equipment cost, especially for thick parts