Use Thermal Imagery For Process Problems

The technique can provide insights on a variety of equipment.

By John Pratten, Fluke Thermography

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Steam traps. Thermal imagers can rapidly check traps and lines into and out of them (Figure 2). If temperature is low in the steam pipe, trap and condensate return, the trap may be stuck closed. If temperature is high in the steam pipe, trap and condensate return, the trap may be stuck open — to make sure it hasn’t just cycled, wait a few minutes and scan it again to see if both sides remain hot. If temperature is high in the steam pipe and trap but slightly lower in the condensate return, the trap probably is operating properly.

Heat exchangers. Thermal inspection can quickly and safely identify areas of corrosion, mineral deposits and sludge build-up, as well as lack of heat transfer due to external damage. Shell-and-tube exchangers often show clear and definitive areas of blockage caused by solids build-up. However, the nature of plate-and-frame exchangers means that clear and sharp temperature difference (?T) lines rarely exist. Higher resolution imagers and on-camera level-and-span adjustments typically help with capturing lower ?T often exhibited by blocked passages or clogged strainers of such exchangers.

Capturing Process Temperature Readings
Thermocouples or other sensors often serve for thermal measurement and control. Economics, of course, limit how many sensors can be installed. A portable thermal imager can determine the optimum spots to locate such sensors, as well as troubleshoot equipment problems.

The imager also can aid in quality control by identifying product defects and lack of uniformity. For instance, it can spot thermal variations in processing some solids or curing some coatings caused by inconsistent moisture levels.

Improving Measurement Results
Objects with low emissivity highly reflect their thermal surroundings. So, reflected energy a thermal imager sees may differ from actual temperature. To compensate to enhance temperature accuracy:

• Avoid measuring shiny metal surfaces.
• In an electrical cabinet, focus on those objects that are highly emissive such as the rubber insulation on the power cable.
• Apply black paint or electrician’s tape to high-emissivity surfaces where necessary.
• Know or control the background temperature.
The other way to compensate is to take qualitative readings. Often you can compare heat signatures between like components or units, or to previous readings on the same object. A markedly different temperature may indicate a problem. Knowing the precise temperature in that case may be unnecessary.

To capture the best thermal images, follow these ten best practices:

1. Verify that the target is operating at a minimum 40% load (lighter loads don’t produce much heat, making it hard to detect problems).

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