BS in Materials Engineering
Materials Engineering Department
A 5/16 in thick, 6 in x 6 in steel plate was used as a simple analog to 4 inch grade “S” steel drill pipe. Ethylene tetraflouroethylene (ETFE) applied as a powder coating was selected as the desired thermally insulating coating because of its excellent chemical resistance, maximum service temperature of 300°C, its thermal conductivity of 0.238 W/m-K, and for its ability to be applied in thicknesses of up to 80 mils. A powder primer coat of approximately 2 mils was applied using a conventional corona electrostatic powder sprayer, and then the high build topcoat was applied directly over the dry primer coat using the same technique to a thickness of about 10 mils. The primer and first topcoat were then cured at an elevated temperature. Subsequent layers of topcoat were hot flocked until a final coating thickness of 60 mils was achieved. To determine the effective thermal conductivity of the coated steel, an apparatus consisting of three contact thermocouples, a hot plate, and polystyrene foam panels was assembled. The hot plate was heated to a constant temperature, then the room temperature coated steel plate was placed under the polystyrene insulation on the hot plate, coated side up. The temperature of both sides of the coated plate was then measured for 30 minutes. The heat flux was then calculated through the bare steel plate. This heat flux value was used to calculate the effective thermal conductivity of the coated plates. The average measured effective thermal conductivities for 40 mil, 60 mil, and 80 mil coatings were 0.82 W/m-K, 0.61 W/m-K, and 0.69 W/m-K respectively.