Infrared camera maps hot spots at steel mills

In steel mills, torpedo cars transport molten steel from the blast furnace to the caster. These special railway cars have long been a costly maintenance issue for steel mills. They must be periodically removed from service to replace deteriorated refractory linings—the brick and cement-like products used to line and protect industrial furnaces—and to expel slag that builds up inside the cars from continual use.

If a torpedo car experiences too much deterioration of its internal refractory, then the steel mill runs the risk of a breakout fault. During such a fault, molten steel leaks through the sidewall of the torpedo car, causing tremendous safety risks to personnel and possibly destroying all nearby equipment. Obviously, breakouts are costly in several areas.

Consequently, steel mills use infrared (IR) techniques to routinely inspect iron ladles and torpedo cars to detect failure modes and thereby save thousands of dollars per year. The IR inspection can detect refractory breakdown before it occurs. Periodically scanning the exterior of an iron ladle with an IR camera enables the technician to accurately determine if the ladle's refractory needs to be replaced. Armed with this information, the technician can project the number of times a ladle can safely be reused before having to spend between $15,000 and $50,000 to rebrick a ladle (replacing the refractory). Identifying "hot spots" also reduces the possibility of molten metal breaking through a ladle or a torpedo car, which would severely damage surrounding equipment, incur high repair costs and production losses, and risk worker safety.

Thermal images are taken of the side of a torpedo car prior to molten steel pouring into it (top) and of the opposite side of a car during the pouring of the molten steel out of it (bottom). Before camera operation, the technician typically sets up the imaging system with a maximum temperature value so that if any part of the car's temperature map indicates a higher value, the car is taken out of service. Temperature maps are used to show the maximum temperature values for a section of the thermal image. Yellow portions of the image show that the surface of the car has exceeded the maximum temperature of 320°F.

For several years IR cameras such as the ThermaCAM Series from FLIR (North Billerica, MA; www.flir.com) have met the challenges of steel-mill excessive-heat and dust-laden environments. Inland Steel Harbor Works (East Chicago, IL) uses these cameras, for example, for both process and predictive maintenance applications.

For torpedo-car analysis, Ircon (Niles, IL; www.ircon.com) has developed the Torpedo Car Inspection System (TCIS), which can be used by mills to visualize hot spots on the outside car wall. Using this system, technicians can control maintenance scheduling and minimize the risk of a breakout. The company's Stinger thermal imaging camera performs a temperature inspection of a moving torpedo car.

The inspection system can be used with either one or two Stinger cameras. Whereas the dual-camera system inspects both sides of the torpedo car as it passes on the way to the molten pour area, a single-camera system can be mounted at the pouring area to provide thermal inspection as the car is rotated during the pour cycle. The NTSC video outputs from the uncooled camera's 320 × 240-pixel IR focal plane are digitized into a PC-based system using a PCI-based 1407 frame grabber from National Instruments (Austin, TX; www.ni.com).

Using the Ircon TCIS, technicians can view, save, and deliver captured image data to a Structured Query Language (SQL) based database such as Microsoft's SQL Server 7.0. If the steel mill uses identification tag readers to track a car's progress, then it can feed tag-reader data directly into the TCIS so that the thermal data are matched to the correct car. Unlike line-scanning systems, which rely on a tachometer to compensate for car speed, a thermal-imaging system can capture an entire image of the moving torpedo car.

Algorithms within the Ircon software compensate for different styles of torpedo cars and ensure that a thermal image of the car is captured during each pass. During operation, each torpedo car rolls into position, stops, and then makes a complete rotation. Molten steel then pours into the opening on the top of the car. Thermal images are taken of the side of the car prior to and during pouring, and, if any portion of the resulting temperature map exceeds a designated maximum value, the car is taken out of service.