RADIOGRAPHIC TESTING [RT]

INTRODUCTION & BASIC PRINCIPLE

Radiographic testing is working on the principle of penetration and absorption capabilities of X and gamma radiation. Radiography is used to test a variety of non-metallic products and metallic products such as welds, castings, forgings, and fabrications. Since it is capable of revealing discontinuities (variations in material composition, or density) in a variety of dissimilar materials, radiographic testing is one of the primary nondestructive test methods in use today. Radiographic testing usually requires exposing film to X rays or gamma rays that have penetrated a specimen, processed the exposed film, and interpreting the resultant radiograph.

For radiographic testing there are two electromagnetic radiation sources are available. One is X ray and another one is gamma ray. Throughout the spectrum, X rays and gamma rays have the same characteristics, and X rays and gamma rays of the same wavelength have identical properties.

APPLICATIONS

Radiographic Testing is most often used for process control during manufacturing, to detect subsurface discontinues in end products such as castings, welds, ceramics and composite materials and electronic components. RT is applied in building and bridge construction, aircraft aviation and aerospace, automotive and space components manufacturing, and aircraft overhaul, maintenance and repair. It is also used for inspecting piping and pipelines, refinery vessels, steel pressure vessels and storage tanks.

ADVANTAGES

RT can be used to detect internal discontinuities in almost any material that is not too thick. X-ray machines capable of penetrating as much as 660 mm (26 in.) of steel, and greater thickness of other materials are available. RT can disclose internal structures, configurations, fluid levels, and fabrication or assembly errors. In most applications, RT provides as image of the test object that can be kept as permanent record. Isotopes are often used for portable application and for field testing.

LIMITATIONS

The major limitations of RT are that the opposing sides of the test object must be accessible, precautions to prevent personnel exposure to radiation are required and configuration of the object must allow for satisfactory formation of shadows of its internal structure.