1 July 2005
Infrared thermography is the tool
Inspections take less time than repairs, especially if done with a thermal imager.
By Jason Wilbur
Is your facility running too hot?
Heat is often an early symptom of equipment damage or malfunction, making it a key performance parameter monitored in predictive maintenance (PdM) programs.
Technicians 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 "reactive" maintenance fees and equipment repair costs, extend the lifespan of machine assets, and further maximize maintenance and production.
Here's the trick: To actually save money, predictive maintenance should not create excessive additional maintenance efforts. The goal is to transition maintenance resources away from emergency repairs and into scheduled inspections of key equipment.
Inspections take less time than repairs, especially if done with a thermal imager. A thermal imager takes noncontact, infrared temperature measurements that capture an object's temperature profile as a two-dimensional picture.
Unlike an infrared thermometer, that only captures temperature at a single point; a thermal imager can capture temperature from both critical components and the entire integrated unit. Thermal imagers can also store previous and current images for comparison and upload images to a central database.
Here is a discussion of the cost savings of thermal imaging (thermography) PdM, the guidelines for successfully capturing and analyzing thermographic data, and a description of how to integrate thermography into a predictive maintenance program.
Calculate the return
Studies by the Federal Energy Management Program (FEMP), estimate a properly functioning predictive maintenance program can provide a savings of 30% to 40% over reactive maintenance.
Other independent surveys indicate that, on average, starting an industrial predictive maintenance program results in the following savings:
- Return on investment: 10 times
- Reduction in maintenance costs: 25% to 30%
- Elimination of breakdowns: 70% to 75%
- Reduction in downtime: 35% to 45%
- Increase in production: 20% to 25%
To calculate the savings at your facility, start by estimating the costs of unplanned equipment failures. Factor in human resources, costs for parts, and the lost revenue from specific production lines.
Then, once your thermal maintenance program is up and running, start tracking the savings. Keep a record of machine asset availability, production output, and the distribution of maintenance dollars and total maintenance costs over time.
Those numbers will help you calculate the return on your thermal imaging and maintenance investment.
Thermography into PdM
Infrared thermography cameras are the first line of defense in a predictive maintenance program. Technicians can quickly measure and compare heat signatures for each piece of equipment on the inspection route, without disrupting operations.
If the temperature is markedly different from previous readings, facilities can then use other maintenance technologies—vibration, motor circuit analysis, airborne ultrasound, and lube analysis—to investigate the source of the problem and determine the next course of action.
For best results, integrate all of your maintenance technologies into the same computer system, so they share the same equipment lists, histories, reports, and work orders. Once the infrared data matches up and dovetails with data from other technologies, the actual operating condition of all assets can read out as an integrated entity.
The upper bearing is failing—the white dot at 202.4.
Applications for faulty
Monitor and measure bearing temperatures in large motors or other rotating equipment.
Identify "hot spots" in electronic equipment.
Identify leaks in sealed vessels.
Find faulty insulation in process pipes or other insulated processes.
Find faulty terminations in high power electrical circuits.
Locate overloaded circuit breakers in a power panel.
Identify fuses at or near their current rated capacity.
Identify problems in electrical switchgear.
Capture process temperature readings.
Inspection process lists
1. Begin by using existing lists of equipment from a computer managed maintenance system (CMMS) or other inventory tool.
2. Eliminate items that are not well suited for infrared measurement.
3. Review maintenance and production records. Prioritize key equipment prone to failure or causes production bottlenecks.
4. Use a database or spreadsheet to group the critical equipment together, either by area or by function, into roughly two-three hour inspection blocks.
5. Use your thermal imager to capture baseline images of each piece of critical equipment. (Note: On some pieces of equipment, you may want to regularly capture multiple thermal images of key components or subsystems.)
6. Download the baseline images into software, and document your route with location descriptions, inspection notes, emissivity, and RTC levels and alarm levels if appropriate.
7. When the next inspection is due, if your imager supports uploading, simply load the previous inspection images onto the camera and follow the onscreen prompts.
To capture the best thermal images, follow these practices:
Verify the target system is operating at a minimum 40% of load. Lighter loads don't produce much heat, making it hard to detect problems.
Get close to your target, and don't "shoot" through doors, especially not through glass. When safety procedures allow, electrical enclosures must be opened or infrared windows or view ports utilized.
Account for wind and air currents. These powerful convective forces cool the abnormal hot spots, often below the threshold of detection.
Account for ambient air temperatures, especially outdoors. In hot weather, the sun can heat up equipment while cold weather can mask the effects of overheating components.
Not all problems are hot. Blown fuses and restricted flow in cooling systems are just two examples of situations where a problem is indicated by a cooler than normal signature. In other cases, a cold component is abnormal due to the current being shunted away from the high-resistance connection. Thermogra-phers must understand how a machine works and what its heat-related failure signatures are.
Consider sources for reflective infrared radiation. Items that have shiny reflective surfaces and are emissive will reflect infrared energy from other nearby objects, including the sun. This can interfere with target temperature measurement and image capture.
Unpainted metals are difficult to measure. To improve measurement accuracy and repeatability, consider affixing "targets," typically paper stickers, electrical tape, or painted spots, to such components.
Accumulate both numeric temperatures and thermal images to facilitate long-term data analysis. Temperature trends will show you where to investigate more and where inspections can be less frequent.
Once you have a database of baseline images, associate an alarm temperature with each one. Upload the most recent version onto your camera before each inspection. If the alarm goes off when you take the new measurement, it indicates a significant change in temperature that needs investigation.
A case of motor bearings
Start with a newly commissioned and freshly lubricated motor, and take a "snap shot" of the motor bearing housing while the motor is running. Use this image as a baseline.
As the motor and its lubrication ages, the bearings wear and heat-producing friction develops in the motor bearing, causing the outside of the bearing housing to heat up. Take additional thermal images at regular intervals, comparing them to the baseline to analyze the motor's condition.
When the thermal images indicate an overheating bearing, generate a maintenance order to replace or lubricate the bearing housing and reduce or eliminate the possibility of costly engine failure.
Leaky gaskets, seals
Finding leaks in sealed vessels is a "snap" when using thermal imagers. Most leaks develop in or around a gasket or seal. Less often, corrosion will cause a weakness to develop and rupture the vessel.
Either way, an infrared imager can diagnose the problem. To find a leaky gasket or seal, scan the imager along the seal looking for thermal eccentricities. A large change in temperature along the seal or gasket indicates a loss of either heat or cold—the "signature" of a failure.
Behind the Byline
Jason Wilbur is the thermography segment manager for Raytek. He has a master's degree in mechanical engineering and an MBA.
Thermal measurement safety
To keep your thermography inspections accurate, effective, and safe, establish written inspection procedures for measurement collection and interpretation.
Following the same steps each time assures you have consistent thermal images in your database for comparison.
When creating inspection procedures, refer to the following standards.
National Fire Protection Association (NFPA) 70E requires all personnel be educated about the risks they face when working near electrical equipment. Personal protective equipment (PPE) must also be available to minimize the risk if an accident should occur. For thermographers, PPE generally includes flash-resistant clothing and a face shield.
The Occupational Safety and Health Administration: OSHA 29 CFR, 1910 Subpart S Electrical, and Subpart I Personal Protective Equipment Safety standards cover electrical systems, safe work practices, and maintenance requirements.
ISO 6781 : International Standards Organization (ISO) (American National Standards Institute) discusses thermal insulation, qualitative detection of thermal irregularities in building envelopes, and infrared methodology.
ASTM International (www.astm.org): ASTM E 1934, 1213, 1311, 1316, and 1256 Standard guide for examining electrical and mechanical equipment with infrared thermography list thermography practices and certifications standards. Also, reference ASTM 1060 and 1153.
The grand scheme of predictive maintenance
Tracking key indicators over time calculates when equipment needs repair.
By Jonathan Blaisdell
Predictive maintenance programs come in all shapes and sizes, depending on a facility's size, equipment, regulations, and productivity goals.
Take a look at these aspects of the practice:
Outlines of some of the most common predictive maintenance methods
An explanation of how to determine the potential cost savings of maintenance improvements
A walk through of a predictive maintenance process
Reactive Maintenance: Run-to-failure approach—letting a system run until something breaks. Maximum cost in terms of revenue lost and equipment replacement.
Preventive Maintenance (PM): Maintenance repairs performed on a regular schedule to minimize component degradation and extend the life of equipment. Preventive maintenance takes place after a set amount of elapsed calendar time or machine run time, regardless of whether the repair is necessary. While more cost-effective than reactive maintenance, preventive maintenance still requires substantial human resources and replacement parts inventories.
Predictive Maintenance (PdM): Tracking key indicators over time to predict when equipment needs repair. 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 person-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.
Reliability-Centered Maintenance (RCM): Prioritizing maintenance efforts based on equipment's importance to operations, its downtime cost in revenue and customer loss, its impact on safety, and its cost of repair. Reliability maintenance depends on the same measurements used in predictive maintenance but saves additional maintenance resources by spending less effort on less important machinery. RCM also requires more training and software than PdM.
Maintenance software, CMMS and AMS: Most facilities practicing predictive maintenance purchase or develop a specialized database, commonly referred to as an asset management system (AMS) or a computer managed maintenance system (CMMS). To track trends, a database system should be able to store:
List of critical equipment
Maintenance and measurement procedures for each type of equipment
History for each measurement
Limits for each measurement (maintenance alarm trigger)
Many systems also track warranty status, depreciation records, and purchasing information and can generate works orders, manage schedules, and track employee training histories and related skills.
Investment in infrastructure
There is plenty of evidence that careful, well-planned maintenance prolongs the life of equipment and prevents costly downtime. Insurance data indicates that roughly half of the damages associated with electrical failures alone are preventable through regular maintenance.
To determine the investments to make in your system, you need to know two things: probability of a failure and cost of the failure. By multiplying these two figures, you can estimate a level of investment in your infrastructure, including maintenance.
Probability of failure: The IEEE 493 standard contains useful data on the failure rates of electrical equipment and techniques for determining the probability of downtime for any given load. For each facility, also incorporate operator knowledge, maintenance history, and manufacturer's specifications, as well as the failure analysis provided by PdM software tools.
Failure Modes and Effects Analysis (FMEA): Used in reliability-centered maintenance, FMEA is a method for analyzing how a system can fail, the impact of the failure, the frequency of failure, and the probability of a hidden failure. The FMEA method assigns risk priority to assemblies based on:
Severity of impact
Probability of occurrence
Probability a failure will remain hidden
For example, for a critical three-phase motor, over-current trip due to phase loss would be failure mode. The probability of phase loss remaining hidden can be high, since the motor may continue to run. To bring hidden failures to the surface, take measurements that closely correlate to the failure mode. In the motor example, current monitoring will quickly uncover loss of a phase on a three-phase motor.
Cost of failure: Unplanned downtime cost variables are:
Lost revenue during downtime, especially critical if the plant is running at or near capacity, or in highly competitive markets. This measurement is in dollars per hour.
Lost revenue due to loss of customer confidence—how many customers will leave you.
Replacement cost of damaged electrical or production equipment.
Repair costs, especially labor.
Cost of scrap.
Cost to clean and restart production.
Insurance premium reductions.
To build a case for preventive maintenance, estimate the cost of failure and compare that to the cost of a maintenance program.
1. Calculate net income per hour of output for your production line or other critical process. Sample: $5,000/hr.
2. Calculate average downtime for each equipment failure and number of events per year. Sample: Failed motor repair requires an average of five hours, and two motors fail annually.
3. Multiply the results of #1 by both values in #2. Sample: $5,000 x 5 x 2 = $50,000 in lost revenue.
4. Estimate labor and equipment repair cost. Sample: $50/hr x 5/motor + $3,000/motor = $6,500.
5. Add #3 and #4. This is your avoidable annual cost in lost revenue + repair. Sample: $50,000 + $6,500 = $61,500.
6. Repeat cost calculation based on planned downtime where no revenue loss occurs. Sample: $50/hr x 5/motor + $3,000 for one new motor + $1,500 for one repaired motor = $5,000.
Utilizing scheduled downtime, the maintenance cost is $5,000 annually with no revenue loss, compared to $61,500 in lost revenues and unexpected downtime costs.
Maintenance program steps
1. Develop a list of critical processes, applications, and equipment, and prioritize each item based on the impact a failure would have. High priority equipment:
Directly impacts safety, the environment, revenue, or customer relations
Is unique or costly to replace, or used constantly (24x7)
Is difficult to find spare parts for or has a long lead time for repair
2. Determine how likely your equipment is to fail, using PdM software, operator knowledge, and maintenance history.
3. Combine those two pieces of information—failure probability and impact—and create an inspection schedule.
4. Set up a database to store measurement results for each piece of equipment. Incorporate baseline data, repair histories, manufacturer recommendations, and operator knowledge (when units broke, how often, why, and what they cost to fix).
5. Test the equipment with the appropriate predictive technologies, and record the measurements in the PdM database.
6. Analyze and monitor your measurements for signs of change in operating conditions: vibration measurements trending up, increased current draw for the same process, current lead to ground, increasing bearing temperatures, and so forth.
7. Investigate any warning signs, and determine if repairs are necessary.
8. Determine the length of time before failure occurs. Again, if you lack the PdM tools to determine this, rely on technician experience and manufacturer data.
9. Schedule repair before failure. One of the powerful PdM paradigms is not to repair equipment too early or too late. Youdon't want equipment to go down, but you also don't want to replace equipment if it will continue to run for a year or more.
10. Use your lead-time to properly align resources, check for spare parts, and choose a shutdown time that minimizes the downcondition in the plant.
11. Make the repair. Document the results, and if appropriate, try to determine the root cause of the failure of the equipment.
12. Take new baseline readings for the repaired or replaced equipment.
Inspection and equipment
Frequency of inspection derives from a number of factors, including safety, the criticalness of the equipment, the expense of a failure, and the frequency with which problems impact production and/or maintenance.
As assets age, are heavily loaded, or are poorly maintained, inspections may become more frequent. When repairs or modifications to equipment happen, conduct a follow-up inspection.
|Equipment type||Max. time between inspections|
|440V motor control centers|
|Non-air conditioned or older||4-6 months|
|Electrical distribution equipment||4-6 months|
|Large motors*||12 months|
|Smaller motors||4-6 months|
|*Assumes vibration analysis, machine circuit analysis, lube analysis, and thermography are on the job.|
Behind the Byline
Jonathan Blaisdell manages thermography products and other PdM technologies for Fluke Corporation. He has a BS in industrial engineering and an MBA.
General equipment list
Motor controls & adjustable speed drives