Date of Award
Master of Science
Michael J Liesenfelt
Michael Howard, Jason P. Hayward
The railroad industry is a vital supply line for a multitude of indispensable industries in the United States, and maintaining a safe and efficient railway systems is of vital importance. Despite a good record of safety, roughly 1000 train derailments occurred in the United States in 2022, and broken rail welds are among the top causes. The utilization of high energy x-ray sources was investigated to determine rail weld integrity and determine minimum flaw size detection limit. A 450 kVp and 3, 6, 9, and 15 MVp x-ray sources were characterized using MCNP6.2 as possible candidates as x-ray sources for world radiographic testing. Each source was then implemented into angular and energy dependent source definitions for use in later simulations. The 450 kVp source was determined to provide sufficient x-ray energy and fluence to provide adequate signal for the Varex 4343 scintillator detector panel. Next, 141 railway was modeled in simulation space and various geometries and filters were investigated to reduce scatter and maintain a quality image. An 18° tilt to the rail section and 1 mm lead filter resulted in sufficient scatter reduction while maintaining sufficient signal strength. This configuration allowed for the detection of spherical voids in the head of the rail down to a diameter of 1.5 mm in simulation space. Further image processing allowed for the detection of an even smaller 0.5 mm void by utilizing an image subtraction method. Finally, factors correcting for beam symmetry and photon attenuation were collected. Initial simulation results provided sufficient confidence to move forward to real world testing.
Hellmann, David, "450 kVp High Dynamic Range Radiographic Inspection of Rail Welds. " Master's Thesis, University of Tennessee, 2023.