The primary production of steel in integrated mills commonly uses Pugh-type railroad cars to transport molten iron from the Blast Furnace process to the Basic Oxygen Furnace Process. Thermal imaging and analysis can be used to monitor the condition of the refractory within these railroad cars. This results in the avoidance of molten metal breakouts on the cars and the maximization of the refractory campaign life. An additional benefit is the significant savings on the maintenance costs of this equipment and greater production efficiencies through planned maintenance practices. These railroad cars are football shaped with an opening at the top and are commonly known as 'subs' or 'bottle cars' in the steel industry. The shell of the vessel serves as both the reservoir for the molten metal and as the structural frame of the car. The interior of the shell is typically lined with ceramic refractory. Periodic applications of gunnite material maintain the integrity of the refractory. Other combinations of materials are also used within the shells of these cars to provide an insulating barrier between the molten iron and the steel shell. In the past these cars were pulled from service for maintenance inspection and repair based on the tons of metal passed through the car during normal production. The refractory condition could not be assessed until the car had cooled down enough for an internal visual inspection. Thermal imaging equipment is now being used to monitor the radiated heat from the shells of these railroad cars to assess the need for maintenance. High and low temperatures are recorded in several different areas of the vessel and are compared with benchmarks developed through several years of measurements and experience. Not only is the hottest temperature of the shell important but also the difference between this and the coldest temperature on the shell. The hottest temperature gives an indication of the thickness of the refractory in a certain area. The difference between the hottest and coldest temperatures gives an indication as to the amount of thermal growth induced stress the shell is exposed to. When the shell temperatures breach the established limits, the car is pulled from service for inspection and refractory lining maintenance. The planning and efficiency of refractory lining maintenance is greatly improved through a well established thermographic monitoring program. Problems that arise earlier than anticipated are quickly noted and rectified, avoiding the cost of product loss and equipment repair or replacement. Refractories that last longer than expected may be left in service to maximize the campaign life of those linings.
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