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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• Remember that small bearing failures can result in fire, mechanical stress, belt wear and increased electrical loads.

When you’re looking at belts and sheaves:

• Guards may restrict your view but thermography still can provide valuable information.

• Be sure to re-inspect belts and sheaves after corrective action is taken.

When inspecting pumps and fans, focus on the coupling:

• Look for irregularities — A healthy coupling should have a consistent thermal signature. Component wear-and-tear cause abnormal heat.

• Alignment issues will show up as excess heat before they cause bearing problems and then irreversible damage.

Inspecting Tanks and Other Sealed Vessels
Most large process tanks have built-in visual or electronic level indicators but these aren’t always reliable. A faulty sensor can lead to overfilling or inaccurate inventory figures for raw materials and finished products. Thermal inspections can reveal actual interfaces between solid, liquid and gas phases, indicating how full a vessel is and whether contents have settled or inappropriately separated.

Pay particular attention to:

• tank levels;
• gaskets and seals;
• valves;
• refractory;
• steam traps; and
• heat exchangers.

Tank levels. Contents of tanks located outside heat up during the day due to solar loading and cool off at night. Liquids and solids have a higher heat capacity than gases and so change temperature much more slowly than gas in the headspace. You can observe this temperature difference between product and headspace through most tank walls. However, at times the gas and liquid or solid may be the same temperature — so level won’t be visible. It will start to become visible as the gas gains or loses thermal energy.

When a vessel is changing temperature, it’s often possible to see the thermal patterns associated with the various phases inside. Knowing the sludge level, for instance, is invaluable when it comes to operating a continuous process or preparing to clean out a tank. Thermography also can reveal floating materials such as wax and foam, as well as layers of different liquids, gases and even solids, such as the layer of paraffin that sometimes forms between oil and water in separators, hindering their normal operation.

You may not discern a level if a tank is completely empty or completely full. Also, thermal imaging may prove difficult if a tank has a shiny surface or insulated walls.

Gaskets and seals. Most leaks develop in or around a gasket or seal. To find a leaky gasket or seal, scan along the seal looking for thermal eccentricities. A large change in temperature along a seal or gasket indicates a loss of either heat or cold — the signature of a failure.

Valves. A thermal imager can monitor control valves for leakage, stiction (sticking) or excess friction. It also can spot if a valve’s excitation coil is overheating from working too hard, pointing to a problem such as current leakage or valve size mismatch.

Refractory. When inspecting refractory insulation, look for hot areas as they may indicate refractory thinning or failure. Cold areas may point to internal product build-up.



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.

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