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Gamma Test NDT

Gamma Test NDT's inspection activities are carried out by their non-destructive inspection personnel certified according to TS EN ISO 9712.

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Turkey

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Overview

Gamma Test NDT's inspection activities are carried out by their non-destructive inspection personnel certified according to TS EN ISO 9712. Within the scope of our activities, among the projects carried out by their organization so far are factories producing pressure vessels, natural gas main pipelines, natural gas installations of industrial facilities, welding controls of ships in shipyards, stadiums, shopping centers, HES Projects, water pipelines within the body of İSKİ, DSİ, Ereğli, and İskenderun Iron and Steel Factories in the iron and steel industry. There are hundreds of industrial establishments. Gamma Test NDT experiences the satisfaction of performing the controls successfully.

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Radiographic Testing

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, the darkening of the film becomes visible as a sign of discontinuity.

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 can 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 a radiation source and the film is used as a 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. After the exposed film is developed, the amount of blackening is checked. The 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. For the film to be read and evaluated properly, illuminated film reading devices should be used, in three types perforated, wired, and stepped to determine whether the applied inspection method is sufficient and the image quality level (sensitivity).

Dye Penetrant Inspection

Penetrant (interference) inspection – Relates to the phenomenon of a rising or escalating liquid as it is confined to a small opening due to the characteristics of capillary action or the surface-wetting properties of the liquid. Penetrant inspection is used to find surface-open discontinuities on relatively smooth, non-porous surfaces. Types of defects that can be found in penetrant inspection: cracks and porosity.

The basic procedure to perform a liquid penetrant inspection consists of the following:

  • Rolled Products: Identifies penetrant anomalies (cracks, seams, or laminations)
  • Castings: Cast discontinuities, hot tears, porosity, air holes, or shrinkage
  • Tattoos: Descriptive cracks, thrusts, or external crevices
  • Welds: To identify cracks, porosity, combustion trough, cold thrust, lack of fusion, or insufficient penetration

There are two basic types of Penetrants available: Fluorescent or Visible. Within each method, there are many methods including water-washable, post-emulsifiable-lipophilic, solvent-removable, and post-emulsifiable-extreme hydrophilic methods. The type and penetrant method are chosen based on sensitivity levels 1 to 4 and depend on site conditions and other variables.

Visual Inspection

It is the examination of conditions affecting the quality such as discontinuities, structural defects, and surface condition on the surface of a product or metal parts, with or without the use of an optical aid (such as a magnifying glass).

Visual inspection can be seen as a very simple method, but it is one of the most important inspection methods. It is mostly work that needs to be done before the application of another non-destructive testing method. Most of the application standards prepared for other non-destructive testing methods require first visual inspection and recording of the findings.

This method can be applied to all metallic or non-metallic materials. Depending on the accessibility to the examination surfaces, it can be applied by using auxiliary devices such as endoscopes when necessary. Surface cleaning is generally not desirable as a preparation for the inspection surface. More precisely, the surface should be such that the expected defects are best visible. The examination is carried out under sufficient light conditions and according to appropriate viewing angles.

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