Interpretation of equipment clues can help diagnose problems before failure occurs
Two of the most useful indicators of equipment problems are temperature and vibration. Most mechanical components emit a certain amount of heat and vibration during normal operation. But excessive heat, cold or vibration can indicate underlying problems, so they can be fixed before they lead to breakdown and bring production to a halt.
New test tools are available to help measure heat and vibration and even interpret the data. They tell end users what the underlying problem may be and guide them in making repairs.
Trouble Heats Up
An abnormally hot or cold spot or an unusual thermal pattern often indicates an emerging problem. That makes handheld thermal imagers, which capture two-dimensional images of the apparent surface temperatures of objects, useful tools for regular predictive maintenance. With thermal imaging, end users can discover and diagnose many issues—including high-resistance electrical connections that impede airflow and bearing issues on motors, tank levels and many mechanical problems.
In a major Florida brewery, scanning with a thermal imager revealed that the gearbox of a bottle labeling machine was running hot—nearly boiling hot. A physical inspection showed water filled the box, not lubricant. A damaged seal allowed the water in. A breakdown could have shut down the bottling line.
One way to prioritize infrared scanning is to begin with critical assets that, if they failed, would threaten people, property or product. Then determine what conditions add stress, and monitor those assets more frequently. For example, the sludge and particulates found in many processes put extra stress on motors—affecting bearings, windings and insulation. That stress can show up as heat. Such motors should be scanned more frequently than others.
Thermal Signals
Use a handheld thermal imager to look for hot spots, cool spots and other anomalies. Be especially aware of similar kinds of equipment that is operating under similar conditions but at different apparent temperatures. Such deviations might signal problems.
A good approach is to create inspection routes that include all critical assets. Each time a piece of equipment is inspected, a thermal image of it should be saved along with the associated data on the computer. With this data, the equipment's condition can be tracked over time. That way, a baseline for comparison is available that will help determine whether a hot spot (or cool spot) is unusual. This will also help verify when repairs are successful.
When a thermal imager indicates a problem, the associated software can be used to document these findings in a report that includes a digital photograph as well as a thermal image of the equipment. That is the best way to communicate the problems found and to suggest repairs.
Vibration
Vibration can be normal in machine operation—or it can be a sign and a source of trouble. Most industrial devices are engineered to operate smoothly and avoid vibration, not produce it. In electric motors, rotary pumps, compressors, fans and blowers, zero vibration is the ideal. In these machines, vibration can indicate problems or equipment deterioration. If the underlying causes are not corrected, the unwanted vibration itself can cause additional damage.
How can the plant maintenance professional differentiate acceptable, normal vibration from vibration that requires immediate attention—service or replacement of the troubled equipment? The common causes of machine vibration are:
- Imbalance— A “heavy spot” in a rotating component will cause vibration when the unbalanced weight rotates around the machine's axis, creating a centrifugal force. The cause could be a manufacturing defect or a maintenance issue. Imbalance can severely reduce bearing life and cause undue machine vibration and heat.
- Misalignment/Shaft Runout—Angular misalignment occurs when the axes of a motor and pump are not parallel. When the axes are parallel but not exactly aligned, that is parallel misalignment. Misalignment may be caused during assembly or can develop over time due to thermal expansion, shifting components or improper reassembly after maintenance. The resulting vibration may be radial or axial (in line with the axis of the machine) or both. Misalignment can cause coupling wear and failure.
- Wear—As components—such as bearings, drive belts or gears—wear, they may cause vibration. When a roller bearing race becomes pitted, for instance, the bearing rollers will cause a vibration each time they travel over the damaged area.
- Looseness—Vibration that might otherwise go unnoticed may become obvious and destructive if the component that is vibrating has loose bearings or is mounted loosely. Looseness can allow any vibration present to cause wear and fatigue in bearings, equipment mounts and other components.
Effects of Vibration
The effects of vibration can be severe. Unchecked, machine vibration can accelerate rates of wear (for example, reduce bearing life), damage equipment, create noise, cause safety problems and degrade plant working conditions. In the worst cases, vibration can knock equipment out of service and halt plant production.
Measured and analyzed correctly, vibration can be used in a preventive maintenance program as an indicator of machine condition and can allow maintenance personnel to target remedial action before disaster strikes.
Hand-held vibration testers are designed and programmed to diagnose the most common mechanical problems of imbalance, looseness, misalignment and bearing failures in mechanical equipment—such as motors, pumps, fans and blowers.
Some testers can quickly detect vibration along three planes of movement then provide a plain-text diagnosis with a recommended solution. This diagnostic technology analyzes machine operation and identifies faults by comparing vibration data to an extensive set of rules developed over years of field experience. It is all done with intelligence built into the tester, without the long-term monitoring, recording and analysis required for typical long-term vibration monitoring programs.
An Ideal Solution
A handheld vibration tester was the ideal solution for the area logistics manager of a major oil company. For the past year, he had used a handheld tester to diagnose issues in pumps (which pump 8,000 barrels an hour), blowers and motors up to 3,500 horsepower.
“The neat thing about it is the Fluke will give you its idea of what it thinks is wrong,” he says. “But it also gives you that signature you can give to the engineers. We went down to our transport station and were able to find some bearing problems on one of our units.”
The tester “called out for a bearing problem. Once we got the pump into the shop we found out the shaft was out of round, which took the bearing out.”
Ease of use is another advantage. “You can give this thing to just about anybody, and they can learn how to use it in a matter of a few minutes. You can log all your equipment, you can pair it up with Fluke's infrared camera, and it will give you a full picture.”
Used together, a thermal imager and vibration tester deliver results fundamental to the company's maintenance program. “With the big motors, we do the vibration analysis, we look everything over on an annual basis with the Fluke imager so we can see if there's any heat rise, and we use it on all the switch gears,” he says. “I call it shoot—fix—move on.”
Pumps & Systems, September 2011
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