|Fig. 1: X-ray of Pooh. (Source: Wikimedia Commons)|
Radiography is a type of non-destructive test. It tests the integrity of certain equipment such as vess equipment such as vessels, pipes, welded joints and castings without causing damage to the material.  It uses radiation.  It uses radiation to produce an image that can show cracks, or areas where the material may not be as strong.  This is very important when determining the strength of say, a weld between pipes that is used to pipes that is used to transport natural gas, or beams that help support a building. Radiographic techniques use different types of rays to pass through products, such as X-rays and gamma rays. Gamma rays are produced during radioactive decay, as opposed to X-rays which can be artificially produced. In contrast to contemporary belief, X-rays have no relation to nuclear energy.
The most common application of radiography uses x-rays.  X-rays are part of the electromagnetic spectrum and have short wavelengths, which allows them to easily pass through matter.  X-rays can be produced using two different processes, Bremsstrahlung and K-shell emission.  In radiographic testing, the material that is being tested is placed between the X-ray machine and radiation sensitive film.  X-rays pass through the material and form shadows on the film.  The film's darkness will vary with the thickness of the material.  Darker areas indicate more exposure (higher radiation intensity), or thinner material, which exposes structural failures. 
Why use X-ray radiographic testing as opposed to other non-destructive tests? X-rays can penetrate many types of materials, as well as detect surface and internal flaws.  It can be us can be used to detect hidden areas without direct access to the surface.  Significant variations in composition can be detected as well.  However, the equipment is relatively expensive and dangerous, as exposure to X-rays can cause adverse health effects. ep>
© Mariah Lee. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Radiation Protection and Safety in Industrial Radiography," International Atomic Energy Agency, January 1999.
 R. H. Bossi, "Radiographic Testing at Lawrence Livermore National Library," Lawrence Livermore National Laboratory, UCID-19366, 12 Apr 82.