Small Controlled Area Radiography – Fundamentals and Technology Advancements

Radiographic testing (RT) is one of the most efficient and economic NDT methods for volumetric inspection; ensuring safe, reliable construction and ongoing use of critical infrastructure around the world. The penetrating radiation from isotope based gamma ray and accelerator based x-ray generators provide a unique mechanism for creating an image based on the differential absorption of photons in a sample. Unfortunately, the mechanisms of photon radiation interactions with matter that allow for weld quality inspection, measurement of corrosion/erosion in pipe wall, etc. create negative externalities in many environments where RT is often performed.  Gamma radiation interferes with critical safety and process control systems. Examples include UV flame detectors, radiation monitoring systems, nuclear level and density gauges, etc. These systems cannot differentiate the gamma rays from a radiography source and the UV photons from a fire or gamma rays from 137Cs sources used in many nuclear gauges.  ALARA – The ever-increasing emphasis on reducing occupational exposure and exposure to members of the general public often requires RT to be performed in shooting windows or during off-shifts reducing overall inspection efficiency.SCAR or Small Controlled Area Radiography is the concept of controlling the radiation utilized for RT allowing for radiographic inspection without restrictive shooting windows (24/7 radiography concept), in close proximity to other trades, and without impacting critical sensor systems. This paper describes the fundamental principles for achieving Small Controlled Area Radiography with an emphasis on the use of 75Se and innovations in SCAR equipment enabling advanced SCAR techniques. Practical SCAR applications covered include:  Near nuclear gauges and UV detectors – typically <0.5 mR/hr  Close proximity to members of the general public – <2 mR/hr exclusion zone at 6 feet  Minimizing/eliminating flash dose  Rope access

References

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