1. The principles of Radiography Testing (RT):

In industrial radiography, the usual procedure for producing a radiograph is to have a source of penetrating (ionizing) radiation (X-rays or gamma-rays) on one side of the object to be examined and a detector of the radiation (the film) on the other side as shown in Picture 1. The energy level of the radiation must be well chosen so that sufficient radiation is transmitted through the object onto the detector.

Picture 1: The principles of Radiography Testing (RT).

The detector is usually a sheet of photographic film, held in a light-tight envelope or cassette having a very thin front surface that allows the X-rays to pass through easily. Chemicals are needed to develop the image on film, which is why this process is called the classic or “ wet” process.

In industrial radiography there are several imaging methods available, techniques to display the final image, i.e. Film Radiography, Real Time Radiography (RTR), Computed Tomography (CT), Digital Radiography (DR), and Computed Radiography (CR).

2. The process of Radiography Testing (RT):

- Exposing a component to the penetrating gamma or X-radiation that passes through the component being inspected.

- Differences in the thickness and density (homogeneity) of the component are proportional to the absorption of penetrating radiation.

- Exposure a radiographic image of the component’s internal features are generated, indicating lighter or darker areas on the image.

Picture 2: Process of Radiography Testing (RT).

3. Advantages and disadvantages of Radiography Testing:

- Advantages:

• Volumetric inspection
• Permanent record
• Detection of surface and subsurface flaws
• Can be used on most materials
• Direct image of flaws
• Real - time imaging

- Disadvantages:

• Equipment can be bulky and heavy.
• Radiation hazards.
• Testing area needs to be controlled access.
• Access to both sides required.
• Limited ability to detect fine cracks.
• Results require interpreting by experienced person.
• High capital outlay and running costs.
• Not suitable for certain configurations, e.g., tee joint.