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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Advances over the last several years have transformed thermal imaging from a tool for the specialist to one that plant personnel can use for regular maintenance and troubleshooting process equipment. A thermal imager enables a technician to diagnose root-cause more efficiently while also often identifying other potential problems during the same inspection.

Unlike regular digital cameras that capture images of visible light reflected by objects, thermal cameras create pictures of heat, essentially measuring infrared energy emitted from objects and then converting the data into corresponding images of temperature. In a “radiometric” imager, each pixel of color on screen represents an individual temperature.
 
Thermal imagers read surface temperature of objects. However, all surfaces don’t emit thermal energy equally well. Emissivity describes, via a scale from 0 to 1, the efficiency with which an object radiates or emits heat. Shiny metals have low emissivity; non-metals and painted or heavily oxidized metals have a higher emissivity.
Specific applications for imagers include: measuring operational temperatures in motors or other rotating equipment; identifying leaks, blockages and settling in sealed vessels, pipes, steam systems and heat exchangers; and capturing process temperature readings. Let’s now look at each of these.

Monitoring motors And Other Rotating Equipment

Key inspection points for motors include:

• Bearings — Bearings under equal load should display equal temperatures. A hotter bearing on the sheave side of a motor could indicate over-tightened belts.
• Belts — Sheaves that are hotter around their circumference could denote slipping belts. Belts that don’t cool between the motor and blower sheaves could signify slipping belts. Belts with unequal thermal patterns could point to misalignment.
• Couplings
• Electrical connections
• Overall temperature — Hotter than usual results could indicate poor cooling or internal problems.

Use the thermal camera every so often to quickly check overall temperature, especially of smaller motors that may not get the kind of maintenance they should. Often these motors overheat before anyone notices. Use the motor temperature rating on its nameplate as a guide. Exterior motor temperatures generally are about 36°F cooler than interior temperatures.

For a routine or preventive maintenance program, it’s ideal to start with a newly commissioned and freshly lubricated motor; take snapshots of key inspection points while the motor is running. Use these images as baselines.

Tip: On new motors, watch the initial startup through your thermal imager. A wiring problem or alignment or lubrication issue will show up thermally before permanent damage is incurred.

As a motor ages and components become worn, heat-producing friction develops; so, its housing will begin to heat up. If possible, take additional thermal images at regular intervals, comparing them to the baseline to analyze the motor’s condition. When thermal images indicate overheating, generate a maintenance order.

Thermography often is the only way to inspect small bearings — plus it checks them while the motor is running.

When you’re examining small bearings:

• Compare thermal patterns of one bearing to similar ones in the same operation (Figure 1).

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