The exhaust tunnel being used at the Savannah River National Laboratory (SRNL) is one of the major underpinnings to the daily processing of radioactive material at the site. The exhaust tunnel, named H-Canyon Exhaust Tunnel, allows for the filtering of certain by-products that are the result of radioactive material refinement. Nitric acid is one of the main chemicals being used at the site to aid in the refinement, where a percentage escapes as vapor into the exhaust tunnel system. Over the years, the acidic vapor has eroded the surface of the concrete walls, exposing the reinforcing steel rebars. This will lead to the weakening of the tunnel wall, which is the only barrier between the tunnel and the outside environment. Structural integrity inspection of the tunnel has been on-going to ensure the safe operation of the facility. Our task is to develop mobile inspection units capable of maneuvering along, and around a duct, to assist in the inspection of the tunnel. Two mobile units are proposed in this work, each based on a different adhesion mechanism. The first makes use of thrust generated by a propeller-based setup, while the second utilizes an impeller-based setup to create suction force, for the mobile unit to adhere to the duct surface. We present the system designs of both of the proposed units, and show the preliminary bench test results on a duct mock-up.