Neutron radiographic detection limits of fluids in metal pipes

Routine maintenance of process pipes at the Savannah River Plant has indicated that undesirable fluids can build up in the various gas lines. Thermal neutron radiography has been used to image thin films of various fluids in thick-walled high-pressure process pipes. A 3.5 x 106 n/(cm2-sec) thermal neutron beam and standard transfer imaging techniques were used to provide radiographs of the fluid-bearing pipes. In addition, a computer graphics procedure was developed that simulated the neutron radiographs; this method permitted examination of some fluid-pipe configurations not studied experimentally. Actual pipe dimensions ranged in OD from 1/4 to 9/16 in. with OD/ID = 3. Many common industrial fluids such as H2O, oils, and CCl4 may be detected in thick-walled process pipes, even when distributed in thin (3 to 10 mil) fluid films. By contrast, fluids with a low thermal neutron cross section (D2O and T2O) can be detected only for much thicker films