April 20, 2006
Spare Parts Tip
Avoid using substitution spare parts as they can be devastating and very difficult to troubleshoot.
If an anti-friction bearing has to be replaced and there is no replacement available, very often a bearing will be used that has a different number of rolling elements but, otherwise, fits the bill by physically having the same dimensions and has similar loading characteristics. If, for example, the old bearing has eight rolling elements and was original equipment, the designers had obviously chosen that type of bearing to avoid any possibility of developing a resonant condition in the machine. However, by installing a substitute bearing with a different number of rolling elements we may have, innocently, created a potential resonance problem which could have devastating results on the machine that it is installed in, or in other machines within close proximity.
The above scenario is,unfortunately, very common and most people ignore the fact that a substitute bearing could be the root cause of their problems for the simple reason that it is a new bearing and could never cause such a problem. As a result, they go off on a tangent trying to find the problem elsewhere. In such a scenario, if a substitute part has to be used to get production moving again, its use should be logged into the work order or CMMS program and be scheduled for change out as soon as the original equipment part is received. If this is not done, I will guarantee that when that bearing fails again it will be replaced with the same type and so the problem perpetuates itself.
In the real world, this is a very common occurrence and can be devastating, so please avoid substitutes.
Most excellent reader tip by John C. Robertson
AMSCO Inc. , Simpsonville SC
Tel: 864-967-7183
Thanks John - your Maintenance Tips hat is on the way!
Get your own Maintenance-Tips Hat by sending in a new Tip here
April 20, 2006
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April 20, 2006
Reliability Centered Maintenance (RCM) Tip
“DIFFERENT PEOPLE” SEE THINGS “DIFFERENTLY”.
To feel confident that equipment obvious problems are recorded and known. Have your RCM Team leave their office for a planned visit to a valuable piece of process equipment. Include some operators, technicians, engineers and interested parties. Arm the participants with a clipboard, paper, pre-numbered cardboard labels and string. Have participants walk over the equipment looking for faults or potential problems and tag and record each found defect. Go back to the office to discuss the recorded observations and then list in order of priority on a whiteboard. You will be surprised at the results. One example we tried this on was, a large Larox belt press filter and we recorded 62 defects after the RCM had been completed “in the office”.
The final trick is to empower the team to get those defect labels removed by rectification.
Most defects found will have to be reported to various departments (electrical etc).
Defects we found were hydraulic oil leaks, water leaks, noisy bearings, worn rollers, loose limit switches even several safety trip hazards.
Reader tip submitted by Greg Quilter, RCMaint Organisation Australia.
(Web site under construction)
Thanks Greg - your Maintenance Tips hat is on the way! We hope to see you wearing it during our visit to the WCEAM - July 11-14, 2006 in Surfer’s Paradise!
Learn more about the First World Congress on Engineering Asset Management
April 20, 2006
Alignment Tip
VERTICAL ALIGNMENT
Whenever an alignment job is being performed on vertical flange-mounted machines or machines which have their feet mounted to a wall resulting in a vertical shaft orientation, it is recommended to correct angularity first and then proceed to correct any offset that is still present between shaft centerlines.
If instead the offset is corrected first and any angularity is corrected subsequently, there is a good chance you will find yourself making a second offset correction unless you are using one of the better alignment systems which take into account the impact on offset from correcting angularity are utilized in the alignment procedure.
Tip provided by LUDECA, INC.
ALIGNMENT * VIBRATION * BALANCING
http://www.ludeca.com
Tel: 305-591-8935
April 20, 2006
Motor Testing Tip
Variable Frequency Drive (VFD) Winding Shorts
Voltage spikes from VFD’s are not the primary cause for winding failure in a VFD driven electric motor. The high voltage carrier frequency (number of pulses) of a Pulse Width Modulated (PWM) drive drops the partial discharge inception voltage into the operating range of the motor/VFD voltage.
This means that there is a capacitive build-up and discharge within small voids and at the end-turns of the motor windings. These discharges cause a buildup of ozone which breaks down varnish and wire insulation. Eventually, a pin-hole short develops.
At this point, the harsher electrical environment of the VFD, including voltage spikes, causes the developed short to act, tripping the motor while it is on the VFD. ‘Spike Resistant’ wire is most often ‘Partial Discharge’ resistant wire with a sacrificial coating on the outer surface, a conductive coating in the middle, then a final insulation system around the conductor. This type of wire insulation system dissipates the capacitive charges before they occur.
This type of failure can be demonstrated in situations where a motor short develops and the motor trips while on a VFD, but appears to run satisfactorily if put in bypass or connected to line voltage on a test bench. When sent into a repair shop, high voltage test methods are often unable to detect these faults as the signal dampens only a few turns into the motor winding and pin-hole shorts tend to occur deeper in the motor winding. As a result, some motors may be sent in for repair and are returned as ‘good,’ but are still unable to work on a VFD. In a standard power environment, they may only last months in operation before the winding finally shorts.
The method used for detecting VFD-related pin-hole shorts is Motor Circuit Analysis which uses a low-voltage AC output and looks for slight changes to the phase angle and current/frequency test results. The first stage may appear as a small shift in test results with the final stages appearing as a larger difference between readings. If detected from the VFD, the test results should be re-tested at the motor as the electrical environment of a VFD can also cause cable insulation failure, if the drive is not properly filtered.
Tip provided by ALL-TEST Pro, LLC
http://www.alltestpro.com
Tel: 860.395.2988
Read Motor Testing Case Studies by ALL TEST
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April 20, 2006
Human Error Tip
Overconfidence is one of the top 10 traps resulting in human error. This is consistent with complacency where we have successfully performed a certain task a thousand times over the years and begin to get a sense of security from this track record. This can result in our overlooking some of the details of the tasks resulting in a human error. Pilots fly the same types of planes day after day but they always go through their checklist each flight to make sure they have not overlooked anything.
Tip provided by the Reliability Center Inc.
Tel: 804-458-0645
http://www.reliability.com
April 13, 2006
Infrared Tip
Choosing the Correct Infrared Equipment
If you are in the market for infrared equipment in your maintenance department, take that little extra time to do your research. The industry has changed dramatically in the last few years with several new players in the market offering more options and features to choose from than ever before.
Since we all have to live within our budgets, cost is often the first thing considered when identifying the correct purchase. Because of this, it is best to approach the process from a Life Cycle Cost perspective rather than a simple Return On Investment approach. Ask yourself what the ramifications would be if a quality infrared camera was needed for your application and a low end camera were to be purchased? How much longer will the inspection routes take? How many anomalies could be missed due to having the wrong tool and what would those costs be?
The first step in this process is to identify your own particular needs to help narrow down the options. Typical maintenance infrared needs fall into one of the three following categories. To determine which is right for you, ask yourself the following questions:
1. Do you need equipment for operations or maintenance technicians to have in their tool bags for random- or rounds-type temperature measurements?
• If so, spot radiometers would work well for this application.
2. Do you have the need to complete follow up checks on electrical repairs made from an outside contractor and perform basic mechanical checks?
• Where visible images are critical but having a high end radiometric camera may not be needed, you should go with a middle of the road non-radiometric camera.
3. Do you need a higher end camera for a route based condition monitoring program?
• In this case you would want to consider a radiometric camera that has quality, easy to use software for reporting.
Once the selection has been narrowed by determining your overall needs, you can begin looking into the features of the equipment in the category you selected. It is highly advisable to research the key infrared features and terminology prior to discussions with vendors if you are not already familiar with the equipment or vendor.
The final step to purchasing an infrared camera is giving it a test drive. Vendors are more than willing to come to your site and let you give their camera a trial run. Take advantage of this offer and don’t skip this step. Just as each car you drive has a different feel, each camera has a different feel and comfort level as well. If you follow these guidelines, you will find a camera that fits your needs and makes you happy.
Tip provided by Dallas Fossum, Reliability Solutions Director, Allied Reliability
April 13, 2006
Predictive Maintenance Tip
Always document “Lost Opportunities” in your predictive maintenance program. “Lost Opportunities” occur when equipment goes down due to an unpredicted failure. This documentation allows the predictive maintenance program to evaluate that the correct technologies and setup are being applied to correctly determine the failure modes on equipment. Also, this documentation can be used as an example to management for identification of additional technologies or additional resources that may be required to identify the equipment failures in the future.
Tip provided by LUDECA, INC.
ALIGNMENT * VIBRATION * BALANCING
http://www.ludeca.com
Tel: 305-591-8935
April 13, 2006
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April 13, 2006
Ultrasound Tip
Clean Sensor Placement is Key to Repeatability
Testing bearings is a critical element of most ultrasound inspection programs and storing data for trending and analysis purposes leads to early detection of advanced wear and lubrication needs. Paying attention to sensor placement is just as important for ultrasonic monitoring as it is for vibration.
One mistake to avoid is taking ultrasound readings through a lot of dirt, grime, and multiple layers of paint. Ultrasounds are low energy sound pressure waves. Their travel from the source (Your bearing) to the destination (Your ultrasonic data collector) depends on a medium that is consistent and continuous. If their journey is interrupted by molecular air gaps, layers of paint, and built-up dirt, what implications does that have for corrupting data? Ultrasonic trending and analysis relies on comparing measurements over time. Clean the sensor placement area to ensure measurements are collected in an environment that’s as free from variables as possible.
This tip supplied by SDT North America
Tel: 905-377-1313
Read Airborne Ultrasound - Predictive Maintenance for the Masses White Paper
