Industrial radiography

Industrial radiography has been used for more than 50 years and is an essential tool of nondestructive testing (NDT) for safety assessment and quality controls in many industries. According to an industry representative who briefed the committee, there are more than 10,000 radiography sources sold globally per year, with about 4,000 of those sold into the U.S. market. There are more than 1,000 licensees of radiography cameras in the United States.3 Industrial radiography relies on transmission and absorption/attenuation of short-wavelength electromagnetic energy (gamma-ray photons and x-rays) to visualize structures such as welds and castings for internal defects or porosity; gas and oil pipes to detect blockage, corrosion, and pipe wall thickness; industrial structures to ensure that there are no cracks or blockages; and aircraft and automobile parts for defects. A gamma radiography camera or x-ray tube directs a beam of gamma rays or x-rays at the item being tested, and a detector (film or electronic) that is lined up with the beam on the other side of the item records the gamma rays or x-rays that pass through the material. The number of photons that pass through the material is proportional to its thickness and density. Because the material is thinner or less dense where there is a crack or a flaw, more photons pass through that area. The detector creates an image from the rays that pass through, called a radiograph, which shows cracks or flaws