MRO Magazine

Feature

Thermal imagers let you see the heat

Predictive maintenance (PdM) is more than just a buzz-word. It involves tracking key indicators over time to predict when equipment will need repair. Why? Because the 'run-to-failure' approach to equi...


Predictive maintenance (PdM) is more than just a buzz-word. It involves tracking key indicators over time to predict when equipment will need repair. Why? Because the ‘run-to-failure’ approach to equipment maintenance just doesn’t work. All it provides is maximum cost in terms of revenue that is lost and equipment that need to be replaced.

Predictive maintenance programs measure equipment on a regular basis, track the measurements over time, and take corrective action when measurements are about to go outside the equipment operating limits. Repairing equipment as-needed requires fewer man-hours and parts than preventive maintenance. However, tracking the measurements requires new tools, training, and software to collect and analyze the data and predict repair cycles.

An integral aspect of PdM is thermography, or thermal imaging. Thermal imagers detect the infrared part of the electromagnetic spectrum. Most cameras operate in the longwave (8 to 14 m) part of the spectrum and produce visual images of that radiation. Infrared is emitted by all objects and the amount radiated increases with temperature. Thermography allows us to see these variations and differences in temperature. Warmer objects will stand out against a cooler background and vice versa.

Of course, heat is often an early symptom of equipment damage or malfunction, making it a key performance parameter monitored in predictive maintenance programs. Machinery and equipment maintenance professionals who practice infrared predictive maintenance regularly check the temperature of critical equipment, allowing them to track operating conditions over time and quickly identify unusual readings for further inspection.

By monitoring equipment performance and scheduling maintenance when needed, these facilities reduce the likelihood of unplanned downtime due to equipment failure, spend less on equipment repair costs, extend the lifespan of machine assets, and further maximize maintenance and production.

Electric motors

Using a handheld thermal imager, you can capture infrared temperature measurements of a motor’s temperature profile as a two-dimensional image. Thermal images of electric motors reveal their operating conditions as reflected by their surface temperature.

Such condition monitoring is important as a way to avert many unexpected motor malfunctions in systems that are critical to manufacturing, commercial and institutional processes. Such preventive actions are important because when a critical system fails, it inevitably increases costs, requires the reallocation of workers and material, reduces productivity and, if not corrected, can threaten corporate profitability and even the well-being of employees, customers or clients.

For a specific motor, you can do an analysis based on the cost of the motor, the average amount of time a line is down from a motor failure, the labour required to change out a motor, etc. Of course, productivity losses from downtime vary from industry to industry. For example, lost production from a papermaking machine can be as much as $3,000 per hour, while in the steel casting industry losses can be as high as $1,000 per minute.

Ideally, you should check motors when they are running under normal operating conditions. Unlike an infrared thermometer that only captures temperature at a single point, a thermal imager can capture temperatures at thousands of points at once, for all of the critical components: the motor, shaft coupling, motor and shaft bearings, and the gearbox. Remember that each motor is designed to operate at a specific internal temperature. The other components should not be as hot as the motor housing.

All motors should list the normal operating temperature on the nameplate. While the infrared camera cannot see the inside of the motor, the exterior surface temperature is an indicator of the internal temperature. As the motor gets hotter inside, it also gets hotter outside. Thus, an experienced thermographer who is also knowledgeable about motors can use thermal imaging to identify conditions such as inadequate airflow, impending bearing failure, shaft coupling problems, and insulation degradation in the rotor or stator in a motor.

In general, it is a good idea to create a regular inspection route that includes all critical motor/drive combinations. Then, save a thermal image of each one on a computer and track measurements over time. That way, you’ll have baseline images to compare to, that will help you determine whether a hotspot is unusual or not, and, following repairs, to help you verify if the repairs were successful.

What represents a red alert? Equipment conditions that pose a safety risk should take the highest repair priority. After that, generally speaking, each 10C rise above its rated temperature cuts a motor’s life in half. Regularly scheduled infrared inspections of electric motors identify motors which are starting to overheat. Even an initial thermal image will reveal whether a motor is running hotter than a similar motor doing a similar job.

If you suspect overheating is the result of one of the following, consider the action described:

Inadequate airflow: If a brief shutdown is possible without affecting the plant process, shut off the motor long enough to perform minor cleaning on the air intake grills. Schedule a thorough motor cleaning during the next planned plant shutdown.

Unbalanced voltage or an overload: The usual cause? A high-resistance connection in the switchgear, disconnect or motor connection box can usually be pinpointed by a thermographic inspection and confirmed using a multimeter, clamp meter or a power quality analyzer.

Impending bearing failure: When the thermal images indicate an overheating bearing, generate a maintenance order to either replace or lubricate the bearing. While somewhat expensive and requiring an expert, vibration analysis can often help you determine the best course of action.

Insulation failure: If it will not too greatly affect production, de-rate the motor in accordance with NEMA standards. Generate a work order to replace the motor as soon as possible.

Shaft misalignment: In most cases, vibration analysis will confirm a misaligned coupling. If a shutdown is possible, dial indicators or laser-alignment devices can be used and the misalignment can be corrected then and there.

Whenever you discover a problem using a thermal imager, use the associated software to document your findings in a report that includes a thermal image and a digital image of the equipment. It’s the best way to communicate the problems you found and the suggested repairs.

Motors are not the only equipment that can benefit from thermographic inspection as part of a PdM program. The performance and life expectancy of all types of machinery and equipment — valves, pipes, vessels, compressors, switchgear, pumps, heat exchangers, gear boxes, bearings, boilers, traps, and particularly electrical equipment and power distribution systems — can be optimized by baseline measurements and careful monitoring for changes.

This article was provided by Fluke Electronics Canada LP, Mississauga, Ont. Fluke offers a specialized PdM portal on its website, along with an extensive thermography online resource library, educational programs, seminars and specialized training. For more information, visit www.flukecanada.ca/pdm.

PHOTO CAPTIONS

Infrared predictive maintenance (1) lets you regularly check the temperature of critical equipment, track operating conditions over time and quickly identify unusual readings for further inspection. What you see (2) isn’t always what you get (3). We can see the element on the far left is running much hotter than the other two — an early indicator of possible failure. Ideally, you should check motors (4) when they are running under normal operating conditions.

Thermal imager combines digital and IR images

The la
test thermal imager from Fluke features IR-Fusion, which provides a combination picture-in-picture infrared/digital image to allow users to identify and correct problems quickly and cost effectively, whether they need to analyze a circuit board close up, measure a power distribution line or monitor fast-moving equipment. A 320 x 160 detector provides high image quality and a 5-in. colour LCD offers improved onsite analysis. The Ergo Flex Design is designed for applications when a clear line of sight isn’t possible, while a Windows CE interface and on-board analytical tools allow for field image analysis. SmartView software offers customizable reporting and an array of image analysis tools.

Fluke Electronics Canada LP