Description: Thermal neutron radiography has been used to image thin films of various fluids in thick-walled high-pressure process pipes. A 3.5 x 10$sup 6$ n/(cm$sup 2$-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 which simulated the neutron radiographs; this method permitted examination of some fluid-pipe configurations not studied experimentally. Actual pipe outer dia ranged from $sup 1$/$sub 4$ to $sup 9$/ $sub 16$ in. (OD/ID = 3), but the graphics method was used for some cases outside this range. Fluids in the thermal cross section range 0.29 cm$sup -1$ less than or equal to $Sigma$/sub th//sup f/ less than or equal to 3.47 cm$sup - 1$ were examined for pipes with 0.099 cm$sup -1$ less than or equal to $Sigma$/ sub th//sup p/ less than or equal to 1.15 cm$sup -1$. For $Sigma$/sub th//sup f/ greater than $Sigma$/sub th//sup p/, the smallest measured film thickness t/sub s/ varied 0.006 to 0.040 in. with decreasing $Sigma$/sub th//sup f/; a semiempirical model described t/sub s/ = t/sub r/ + t/sub a/, where t/sub r/ corresponded to resolution and t/sub a/ depended on the bulk attenuation strength of the fluid. For $Sigma$/sub th//sup f/ less than $Sigma$/sub th//sup p/, part of the fluid film t/sub m/ was masked by the pipe. The calculated physical film thickness t/sub p/ = t/sub a/ + t/sub m/ ranged from 0.003 to 0.035 in. for smallest detected fluid films. Detection of low $Sigma$/sub th/ fluids was improved as much as 60 percent when the pipes were tilted 60$sup 0$ toward the neutron beam. Other options for improved detection were investigated using simulated radiographs. (auth)
Date: January 1, 1975
Creator: Winn, W.G.
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