Condition monitoring is the process of monitoring a parameter of condition in machinery, such that a significant change is indicative of a developing failure. It is a major component of predictive maintenance. The use of conditional monitoring allows maintenance to be scheduled, or other actions to be taken to avoid the consequences of failure, before the failure occurs. Nevertheless, a deviation from a reference value (e.g. temperature or vibration behaviour) must occur to identify impeding damages. Predictive Maintenance does not predict failure. Machines with defects are more at risk of failure than defect free machines. Once a defect has been identified, the failure process has already commenced and CM systems can only measure the deterioration of the condition. Intervention in the early stages of deterioration is usually much more cost effective than allowing the machinery to fail. Condition monitoring has a unique benefit in that the actual load, and subsequent heat dissipation that represents normal service can be seen and conditions that would shorten normal lifespan can be addressed before repeated failures occur. Serviceable machinery includes rotating equipment and stationary plant such as boilers and heat exchangers.
What can we do differently to become proactive rather than reactive?
Visual inspection and non-destructive testing may be undertaken utilising thermal imaging. Slight temperature variations, are key indicators of failing components which may be seen across a surface.
These degrading components, such as failing electrical contacts and terminations as well as bearings, couplings, conveyor rollers, and storage tank internal build-up are indicated through a heat signature whereby application of thermal imaging can be used to successfully identify these potential problem areas and set plans in motion to remedy before they destruct.
A key indicator of an electric motor’s operating conditions is its case surface temperature. To avoid unexpected motor malfunctions in systems that are critical to manufacturing, commercial and institutional processes, condition monitoring should take place.
These preventative actions are important to organisations as the potential failure of possibly critical equipment has a direct bearing on a company’s profitability through production down time as well as the H&S of clients, customers and employees. Due to having to attend a breakdown in a manufacturing process for example, profits are reduced through a break in the actual manufacturing process as well as having to reallocate workforce to deal with the breakdown.
What equipment can I check and when should I check it?
All equipment should be checked ideally when operating under normal 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.
Examples of key critical components that may be surveyed are as follows:
- Air handlings systems i.e. AHU’s, FCU’s
- Storage vessels
- Underfloor heating.....the list is endless.
A piece of equipment i.e. an electric motor is designed to operate at a specific internal temperature whereas all the other components such as the bearings should not operate at the same temperature as the housing. The standard operating temperature should be listed, on the nameplate, on most motors.
While infrared cameras cannot see the inside of a motor, the exterior surface temperature is a good indicator of the internal temperature. General indicator is a +20 degrees difference from the top of the motor case to the bottom of the case indicating internal breakdown of windings of a motor.
When a motor gets hotter within, the temperature also increases on the surface.
Conditions, such as inadequate airflow, impending bearing failure, shaft coupling problems, and winding insulation degradation in the rotor or stator in a motor, can be identified by an experienced thermographer, who is also knowledgeable about both building services and electric motors.
In general, it is a good idea to create a regular inspection routine that includes all critical motor and drive combinations, and then arrange a base line thermal image of each asset which will be saved. The thermal image enables tracking measurements over time, giving baseline images to compare to, that will help determine whether a hotspot is unusual or not and following repairs, to help you verify if the repairs were successful.
The highest repair priority should always be given to equipment conditions that pose any form of health and safety risk. After this, consider that each motor has a maximum operating temperature (that usually appears on its nameplate) and represents the maximum allowable increase in temperature of the motor above ambient. Most motors are designed to operate in ambient temperatures that do not exceed 40 °C. Each 10 °C rise above its rated temperature cuts a motor’s life in half, generally.
Electric motors, which are beginning to overheat, can be identified through regularly scheduled infrared inspections. Whether a motor is running hotter than a similar motor doing a similar job can be revealed by an initial thermal image.
Cost of failures
A simple cost exercise may be carried out on a specific piece of equipment and in this case, an electric motor whereby analysis may be undertaken based on the cost of the motor, the average amount of time a manufacturing line is down from a motor failure, the labour required to change out the motor, etc… Productivity losses from downtime will naturally vary from industry to industry. So for example, lost production from a papermaking machine can be as much as £3,500.00 per hour while in the steel casting industry losses can be as high as £1,500.00 per minute.
Causes and remedial actions
Taking an electric motor as an example, below is a basic fault finding and remedy guide.
|Motor housing||Overheating||Reduced inadequate airflow (also see bearings, windings and insulation below)||Shut off the motor long enough to perform minor cleaning on the air intake grills if a brief shutdown period is possible. Scheduling a thorough motor cleaning during the next planned plant shutdown is also advisable. Ensure that the motor casing fan is indeed in tact.|
|Connections & switchgear||Overheating||Unbalanced voltage or an overload||A high-resistance connection within the terminal box is generally a key cause of impending failure. A thermographic inspection usually pinpoints this problem whereby the problem can be confirmed using a multi-meter, clamp meter or by further testing with a power quality analyser. The control panel that the motor is connected to should also be thermally checked to further verify where unbalanced loads are suspected.|
|Bearings||Overheating||Misalignment, over tensioned drive belts, worn bearing journals and housings||Generating a maintenance regime to either replace the bearing or lubricate the bearing should be done when thermal images indicate an overheating bearing. While this option can be somewhat expensive, vibration analysis can often help you determine the best course of action.|
|Insulation & windings||Overheating||Overload, poor power condition, high effective service factor, frequent stops/starts and environmental reasons||De-rate the motor if it will not impact production too greatly. Generate a work order to rewind or replace the motor, whichever is more cost effective as soon as possible.|
Using our software and experience gained over many years of condition monitoring, you will receive a comprehensive report i
The most commonly used method for condition monitoring rotating machines is called vibration analysis. Measurements can be taken on machine bearing casings with seismic or piezo-electric transducers to measure the casing vibrations, and on the vast majority of critical machines, with eddy-current transducers that directly observe the rotating shafts to measure the radial (and axial) vibration of the shaft. The level of vibration can be compared with historical baseline values such as former start-ups and shutdowns, and in some cases established standards such as load changes, to assess the severity.
Interpreting the vibration signal obtained is a complex process that requires specialized training and experience. Exceptions are state-of-the-art technologies that provide the vast majority of data analysis automatically and provide information instead of data. One commonly employed technique is to examine the individual frequencies present in the signal. These frequencies correspond to certain mechanical components (for example, the various pieces that make up a bearing) or certain malfunctions (such as shaft unbalance or misalignment). By examining these frequencies and their harmonics, the analyst can often identify the location and type of problem, and sometimes the root cause as well. For example, high vibration at the frequency corresponding to the speed of rotation is most often due to residual imbalance and is corrected by balancing the machine. As another example, a degrading bearing will usually exhibit increasing vibration signals at specific frequencies as it wears. Special analysis instruments can detect this wear weeks or even months before failure, giving ample warning to schedule replacement before a failure which could cause a much longer down-time. Besides all sensors and data analysis, it is important to keep in mind that more than 80% of all complex mechanical equipment fails accidentally and without any relation to their life-cycle period.
Please contact us to discuss your condition monitoring requirements, whether it is to set up an annual, bi-annual or quarterly contract or simply just a one off visit, we have the package to suit your needs.
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