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The radiographic inspection method is one of the most widely used non-destructive inspection methods in the industry, as it is a very sensitive inspection method and the inspection results can be recorded permanently.
The test piece is irradiated with a beam of radiation (x or gamma rays) from a source. As the radiation passes through the material, it is absorbed and lost at a certain rate depending on the property of the material, and then reaches the film placed on the back surface of the part and affects the film. Since the discontinuities weaken the radiation differently, the intensity of the radiation passing through the regions with the discontinuities and the darkening it will create on the film will also be different. After the development of the film, darkening on the film becomes visible as a sign of discontinuities.
This method is applied to ferromagnetic and non-ferromagnetic metals and all other materials. X-rays are widely used in non-destructive testing, as they provide the opportunity to examine the internal structures without damaging the materials.
Electrically generated x-rays and gamma rays emitted from radioactive isotopes are absorbed by the material they pass through. As the thickness increases, the amount absorbed increases. Hence, more radiation is absorbed in denser material. X and gamma rays are electromagnetic waves and the difference between them is that they have different wavelengths. Since the wavelengths of X and gamma rays are very small, they cannot be seen with the naked eye and have the ability to pass through materials. X and gamma rays have similar properties to light and affect the silver bromide crystals on the film. They form an image according to the ratio of radiation intensity reaching the film. The most basic rule in industrial radiography is to have a light source on one side of the material and a detector on the other. X or gamma ray source is used as radiation source and film is used as detector. The energy of the radiation source should be chosen at a higher power than the material will absorb. The parameter that determines the ability of the energy to pass through is the wavelength of the light. The smaller the wavelength, the greater the penetrating power. In x-ray radiography, the penetration power of x-rays is adjusted by the voltage applied to the x-ray tube. The film, which detects the rays reaching the other side through the material, is usually placed in an opaque envelope and placed on the back of the material being tested. The rule to be considered here is that the front surface of the envelope is made of material that can easily pass the rays. The image created by X-rays on the film is similar to the shadow cast by a normal light source. Unlike the shadow, the density of the image formed on the film changes depending on the thickness and density of the material. The clarity and size of the image depend on the size of the radiation source, the distance from the radiation source to the film, and the distance of the material from the film. After the film in the cassette is placed behind the test piece, it is exposed to x-rays for a certain period of time. After the exposed film is developed, the amount of blackening is checked. Darkening of the film is called density for short. The presence of different densities in the film indicates that there are different structures in the tested piece. The parts of the film that receive more radiation darken more. This means that the film density is high in this region. For example, if there is a gap in the examined region of the material, the beam will pass through this gap without loss, and therefore this area will appear blacker on the film. In order for the film to be read and evaluated properly, illuminated film reading devices should be used, and also in three types as perforated, wired and stepped in order to determine whether the applied inspection method is sufficient and the image quality level (sensitivity).
penetrameters should be used. The advantages and disadvantages of the radiographic examination method can be listed as follows.
Advantages;
-Provides permanent recording that can be viewed at a different place and time than the test environment.
- Suitable for thin parts.
-The sensitivity is shown on each film.
-Can be applied on any material.
Disadvantages
- Generally not suitable for thick pieces.
- May be harmful to health.
- Direct heat is required for two-dimensional errors.
-the film needs to be exposed and viewed.
- Not suitable for automation.
-not suitable for automation.
- Not suitable for surface defects.
It does not give direct information about the depth of the fault below the surface.
The radiation source can be x-ray or gamma-ray. This image is caused by voids or thickness/density changes within the material. This visualization of the internal structure of the material is called radiographic examination. If a radiographic detector is placed on the back of the material instead of a film, the radiation passing through the material is detected and transferred to a monitor, the direction called Radioscopy in the technique.
