Key Elements for Better Infrared Thermography

By R. James Seffrin, Director, Infraspection Institute

Successful thermography begins long before actual field work begins. The final results for any project depend upon understanding the task(s) to be performed, selection of equipment, operator skills, inspection techniques and documentation of findings. Failure to understand how these factors contribute to the final conclusions can lead to serious errors. To ensure optimum results, a thermographer must understand the nature and reason for the inspection, all equipment and operator limitations, site conditions and how to document findings.

The use of infrared thermography for predicitve maintenance (PdM) and condition-based monitoring (CBM) is now widely recognized. The benefits of infrared thermography coupled with lower equipment costs have led to a greater public awareness of common applications. Research continues to broaden the applications of thermography. Advances in equipment now allow thermographers to routinely perform tasks that could only be dreamed of as little as 10 years ago.

Common applications of infrared thermography now include electrical and mechanical systems, building envelopes, insulated roofs, petrochemical processes, transportation and medicine. In the manufacturing environment, the ability to distinguish high temperatures in rotating equipment, especially motors, allows maintenance organizations to apply highly effective predictive and preventive strategies. This is because a thermal image makes immediately clear what part of the motor is overheating, and to what extent.

According to infrared camera maker Fluke Corp., standard practice for thermographic imaging follows three basic methods:

1. Regular comparison of the operating temperatures of like equipment, performing similar functions
2. Regular comparison of the operating temperature of a single unit to manufacturer’s standards
3. Regular comparison of the operating temperature of a single unit to previous images of the same unit

Since the thermographer guides the infrared inspection process, his/her knowledge is of the utmost importance. Thermal imaging can be used to identify several conditions such as inadequate airflow, unbalanced voltage, impending bearing failure and insulation degradation in a motor’s rotor or stator. It can also identify heat produced by shaft misalignment.

Regardless of the application, however, the final results of a thermographic inspection depend upon understanding the task to be performed, selection of equipment, operator skills, inspection techniques and documentation of findings. Before embarking on an inspection, a thermographer needs to consider and understand how these factors will influence final results. The following steps outline the basic elements a thermographer needs to consider for a successful inspection in any environment.

Define the task

Perhaps the most important—and often most overlooked—part of thermography is the need to define the project. Before any successful task can begin, the thermographer must determine exactly what is to be done and what is expected of the final results. In the case of routine inspections of industrial equipment, this will typically be understood. Infrared can and should be included in normal maintenance “rounds” to establish benchmark results for ongoing comparison.

In non-routine situations, however, specific details are needed to ensure a useful inspection. For example, a thermographer may be asked to “conduct an infrared scan to locate wet areas” on a facility’s roof, a request that does not adequately define the task. It is unclear when the work is to be performed, what type of imager is be used and what type of documentation may be required. But regardless of inspection type, it is always desirable for the thermographer to fully comprehend all aspects of what is expected. If the inspection requires skills beyond thermography, the thermographer, if qualified, may elect to perform these tasks or work with others who are qualified. Once the exact nature of the task has been determined, a scope of work can be developed.

Thermographer qualifications

The operator may be the greatest limiting factor in thermography. Although thermal imagers have their limitations, thermographers can overcome this by selecting the proper equipment (discussed later). Since the thermographer is the most important factor in thermography, knowledge is of the utmost importance. Unless otherwise specified, it is usually not enough for a thermographer to understand only how to operate a thermal imager to produce thermograms. At a minimum, the thermographer should have completed a Level I thermography training course. Thermographers who perform inspections involving temperature measurement should be trained to at least Level II.

The professional thermographer needs a thorough understanding of infrared theory and heat-transfer principles and how site conditions and weather can influence results. At a minimum, a thermographer must also have a basic understanding of the equipment or systems to be inspected. When a thermographer is unfamiliar with the items to be inspected, it is his/her responsibility to gain the knowledge necessary to properly conduct the infrared inspection. To this end, a thermographer must always be an expert in his/her field and be able to honestly recognize personal limitations. Anything less compromises the final results of an inspection before it begins.

Equipment selection

The second greatest limiting factor in thermography may be the thermal imaging equipment itself. Even the best thermographer cannot compensate for equipment that cannot produce the desired information. Fortunately, today’s wide selection of equipment provides many choices for accomplishing the task at a wide range of price points. Modern thermal imagers offer features that not only make thermal imaging easier but provide more capabilities. Unfortunately, the wider selection of equipment tends to make equipment selection more difficult. And while prices on good-quality IR equipment have been dropping for some time, when it comes to imager performance, cost should be considered last.

While most maintenance organizations are confined to working with the infrared equipment on hand, situations can arise where the thermographer can select from one or more pieces of different equipment to do an inspection. Important criteria for such selection include the spectral response of the imager, color options, visual and measurement fields of view, radiometric capabilities, operating limitations and image recording. The use of accessories such as filters, heat shields and special lenses might also be required. Other important considerations include operating temperature, imager controls, display screen and whether imager is intrinsically safe.

A thermographer must always be aware of the capabilities and limitations of his/her equipment. Equipment should be maintained in good working order and calibrated in accordance with the manufacturer’s recommendations. A thermographer must also be able to honestly recognize limitations of his/her hardware.

Site conditions

Prior to conducting an infrared inspection, all pertinent site conditions must be considered. Limitations regarding the use of photographic equipment might preclude the use of certain equipment. Other site conditions which need to be addressed include the accessibility of the equipment to be inspected, radiation levels, airborne particles, sterile requirements and the presence of hazardous or explosive areas.

It is the responsibility of the thermographer to speak with site safety personnel prior to a project to identify pertinent site conditions and determine how these conditions will affect the work to be performed. When working near energized electrical equipment, for example, precautions must be taken to protect personnel from electric shock and arc flash hazards. Weather and environmental conditions also have a significant effect on thermal imaging and must be considered when conducting any outdoor inspection. At a minimum, this should include the following factors:

• Intense summer sunlight can make imaging work difficult.
• High winds can obscure temperature exceptions.
• Precipitation usually cancels outdoor work altogether.

Even normal weather conditions play a role in outdoor thermography. In the case of an infrared roof inspection, for example, the amount of daytime solar loading and wind will have a direct effect on the post-sunset thermal patterns regardless of weather conditions at night. Often, daytime weather conditions can influence the subject structure or systems for several hours after sunset.

To ensure optimum results, a thermographer needs to understand and consider how weather conditions will affect final results. When weather is less than optimum, a work postponement may be the wisest decision.

Documentation

The final documentation of an infrared inspection is the formal record of a project. Plant requirements may vary in this regard, but proper documentation will detail how and when an inspection was performed; who performed the work; weather conditions; any special procedures followed; the results of the work; and conclusions or recommendations. The report should also include all relevant graphics, photographs and thermograms.

With the advent of more sophisticated imaging equipment and advances in computers, thermograms are no longer limited to monochrome prints. Color thermograms, video recordings and digital images are now more common. Laptop computers and powerful software allow the thermographer to prepare reports while in the field. Above all, the report should be clear and sufficiently document inspection techniques and site conditions in order that future inspections may be carried out under similar circumstances.

Keep in mind that successful thermography begins long before the actual field work begins. The final results for any inspection depend upon understanding the task(s) to be performed, selection of equipment, operator skills, inspection techniques and documentation of findings. Failure to understand how these factors contribute to the final conclusions can lead to serious errors. To ensure optimum results, a thermographer needs to understand the nature and reason for the inspection, all equipment and operator limitations, site conditions and how to properly document his/her findings.  MT

R. James Seffrin is a Level III Certified Infrared Thermographer and Director of Infraspection Institute located in Burlington, NJ. He has over 30 years experience in performing infrared inspections for a wide variety of commercial, industrial and residential applications. Jim is also a co-author of several industry standards and qualified as an expert witness on the subject of thermography.

IR Imaging Gives Fast Results on Gearbox Health

The ability to determine lubrication health is another key IR capability, and should be included in any PdM program. The lifeblood of any gearbox is the oil that lubricates its gears. If oil loses its ability to lubricate—or the level of oil gets too low—the gearbox will overheat and eventually fail.

Traditional preventive maintenance for gearboxes has consisted of regular oil-level checks and replenishments as needed. Some maintenance departments add a predictive element to gearbox maintenance in the form of oil sampling and analysis. Oil analysis, usually performed by an outside laboratory, reveals if the oil in a gearbox has lost its ability to lubricate. It will also detect any metal particles in the oil, a sign of gear wear that foreshadows possible failure.

While effective, oil sampling is relatively time-consuming, and can be costly. It can also require equipment shutdown. Moreover, gearboxes often are inaccessible or in unsafe locations, which can make oil-level checking and oil sampling difficult. For these reasons, thermal imaging is a good alternative PdM approach. Since gearboxes generally overheat before they fail, an infrared (IR) camera can detect when a unit is running hotter than normal and/or hotter than similar gearboxes performing similar work in similar environments.

Because thermography is a non-contact, non-destructive technology, even inaccessible gearboxes in dangerous locations can be scanned while running. The IR camara can be used to capture all thermal images as well as visible-light digital images of all units that are running hotter than normal. These processes can also reveal leaking seals where hot oil is running down the sides of gearbox cases.

Be aware that any excessive heat generated in mechanical gearboxes is the result of friction, and that inadequate lubrication is not always the source. The cause could also be faulty bearings, misalignment, imbalance, misuse or just normal wear. Still, thermography is a good first step toward a complete analysis of the condition of any gearbox.

Source: Fluke Corporation

The Trained Eye Best Sees Infrared’s Benefits

Aside from test equipment, training is the most important investment a company will make in an infrared inspection program. While advances in technology have provided a wide range of user-friendly infrared equipment, infrared thermography is not a “point and shoot” technology. Structured training will enable thermographers to better understand what infrared cameras can do, the common error sources that can influence observed thermal data, and the many ways to interpret infrared images. Infrared’s various benefits in electrical and mechanical systems are two examples of the potential value and scope of an infrared inspection conducted by a trained thermographer. 

Electrical: 

As electrical current flows through a conductor, heat is generated. Many electrical defects are accompanied by a rise in temperature for up to several weeks prior to failure. Some defects may be represented as cool components.

Infrared imaging can detect:

• Loose/deteriorated connections
• Overloads
• Imbalanced loads
• Open circuits
• Inductive heating
• Harmonics
• Defective equipment

Mechanical:

As mechanical devices operate, heat is generated. Forces such as friction, misalignment and improper belt tension cause excessive heating.

• Infrared imaging can detect:
• Misalignment of coupled equipment
• Over/under lubrication of bearings
• Over/under tension of belted systems
• Excessive friction
• Defective equipment

Source: Infraspection Institute