Non-destructive testing (NDT)

Scientific Basis

High-energy electromagnetic waves (radiation) can penetrate many materials. Radiation that penetrates a particular material can also affect radiation-sensitive films placed on the other side of the material. When these films are later subjected to a bath process, an image of the inside of the material through which the radiation passed is produced. This image is formed due to voids or thickness/density changes within the material and is called radiography. If a detector is placed on the back side of the material instead of a film and the radiation passing through the material is collected and transferred to a monitor, this technique is called radioscopy.

Applications

It can be used to detect expected volumetric and surface defects in all metallic or non-metallic materials.

Limitations

The thickness of the test piece cannot exceed certain values depending on the type of radiation source used. Suitable material thickness ranges for various radiation sources are given in application standards. It can be applied to any material other than thickness limitations. The operator's training and experience are very important. Both surfaces of the test piece must be accessible for inspection. The equipment used for inspection is more expensive than other methods. It requires careful work especially in terms of radiation safety.

Implementation

Various radiation sources can be used for radiographic examination. These sources can be X-ray tubes or isotopes that produce gamma rays. The X-ray energy range used in industrial radiography is generally between 50 kV and 350 kV. The radiation energy varies depending on the type and thickness of the material being radiated. The most well-known and used gamma sources are Ir 192 and Co 60. In addition to these, isotopes such as Se 75, Yb 169 and Tm 170 are also used in industrial radiography. In order for the inspections to provide healthy and reliable results, they must be carried out according to the standards. These standards are prepared according to the type of material and/or product. There are also application standards that provide acceptance levels and application standards that provide the inspection procedure. Appropriate standards are determined according to the properties of the test piece and inspections are carried out.

EN and ISO Standards Used General:

• EN ISO 5579 - Non-destructive testing - Radiographic examination of metallic materials using film and X- or gamma rays - General principles
• EN ISO 19232-1 - Non-destructive testing - Image quality of radiographs - Part 1: Image quality indicators (wire type) - Determination of image quality value
• EN ISO 19232-2 - Non-destructive testing - Image quality of radiographs - Part 2: Image quality indicators (step/hole type) - Determination of image quality value
• EN ISO 19232-3 - Non-destructive testing - Image quality of radiographs - Part 3: Image quality classesEN ISO 19232-4 - Non-destructive testing - Image quality of radiographs - Part 4: Image quality values and image quality tables evaluated by experiment
• EN ISO 19232-5 - Non-destructive testing - Image quality of radiographs - Part 5: Image quality indicators (Double wire type) - Determination of the total unsharpness value

EN 1330-3 - Non-destructive testing - Terminology and vocabulary - Part 3: Terms and definitions used in industrial radiographic testing

Sources:

• EN ISO 17636-1 - Non-destructive testing of welds - Radiographic testing - Part 1: X- and gamma-ray techniques with film
• EN ISO 17636-2 - Non-destructive testing of welds - Radiographic testing - Part 1: X- and gamma-ray techniques with digital detectors
• EN ISO 10675-1 - Non-destructive testing of welds - Acceptance levels for radiographic testing - Part 1: Steel, nickel, titanium and their alloys

Castings:

• EN 12681 - Castings-Radiographic examination

Steel pipes:

• EN ISO 10893-6 - Non-destructive testing of steel tubes - Part 6: Radiographic testing of the weld seam of welded steel tubes for the detection of imperfections
• EN ISO 10893-7 - Non-destructive testing of steel tubes - Part 7: Digital radiographic testing of the weld seam of welded steel tubes for the detection of imperfections