Thermal Imaging for Maintenance 101

Thermal imaging plays an integral role in maintenance, including predictive maintenance (PdM). It can be used in virtually any application, from power to manufacturing to building maintenance.

Here, we’ll discuss the basics of how infrared thermal imaging works, why it’s important, and how it’s used in various applications.

Thermal Imaging Basics

Infrared imaging is an effective tool simply because heat energy is everywhere. It’s generated inside buildings, bounced off of them, and absorbed back in. Heat is produced at power plants, sent to our cities, and we use it up.

About Infrared Energy

All that energy is just below the range of light visible to the human eye (“infra” = “below”). Infrared technology simply allows us to see the range of light produced by heat that’s normally invisible to us. Think of it as a magic pair of glasses that let you see in a different wavelength.

Another way to think of infrared light is when you turn on a burner on your stove. As the burner gets warmer, it glows orange. If you turn off the lights, you can see it more easily. Infrared light is similar in that it’s produced by heat, but at a different wavelength.

Infrared Wavelengths

Infrared comes in three wavelengths:

• Short wave infrared, which is 1.3 to 2.5 microns in length and is used for night vision.

• Mid-wave infrared, which ranges from 3 to 5 microns.

• Long-wave infrared, which is 8 to 14 microns and has seen the most use in infrared cameras.

Most people who work in maintenance are likely familiar with long-wave infrared since that’s what most cameras have used in the last 20 years. That said, mid- and short-wave infrared have seen some use as well.

Convection and Conduction

Infrared imaging works based on how heat energy behaves. The universe is always trying to equalize itself. If there’s heat in one place—such as an object we’re putting energy into—it will radiate out into space (convection) or transfer into cooler objects (conduction).

To understand conduction, put your hand on a table. You’ll feel the table get warmer. That’s because the heat from your hand conducts into the cooler table.

Convection works a similar way. Put your hand near your face. As long as you’re not in a hot environment like a boiler room, your face should warm up because you’re blocking the transfer of heat into the atmosphere around you.

With an infrared camera, the radiation of heat energy off of objects goes at the speed of light into the detector (i.e. the camera’s lens).

Infrared Imager History and Current Technology

Commercially, infrared technology started in the 1940s, built up in the 1980s, and then exploded in the 2000s.

From the Beginning

The very beginning of infrared imaging was the evaporograph, a device that creates an infrared image using evaporation. As the market developed and people started using infrared for various tasks—including maintenance—manufacturers started building a wider variety of cameras.

Smaller, Faster, Cheaper

In the last 10 to 15 years, the actual quality of cameras hasn’t increased much. Most of the energy that manufacturers have put into developing new cameras has been in the arena of making them smaller, lighter, and faster; eliminating the need for coolers; and making them cheaper overall.

While infrared cameras used to be bulky and expensive—often costing between $50,000 to $80,000 each—you can now get models that plug into the bottom of your smartphone for $200 to $300. They don’t produce the most presentable picture, but they’re comparatively good for the cost.

Modern Infrared Cameras and Cost

A wide range of cameras are available for thermal imaging. They come in different ranges of quality, and it’s not always immediately obvious how much they’re going to cost just by looking at their form factor. As such, a bit of research is needed. Some are as cheap as $100, some mid-range quality models (producing 320 x 240 resolution pictures) might cost up to $700, and higher-end cameras could range from $10,000 to $25,000.

Specialty cameras—such as those fixed to helicopters, used on drones, or designed for specialty tasks like detecting gas leaks—can get even more expensive still. These cameras are intended for tasks that warrant that level of expense.

Infrared Imager Selection for a Particular Project

When choosing an infrared camera for your project, you’ll want to consider the following:

• Ergonomics

• Portability

• Cost

• Electronics

• Expandability

• Ruggedness

• Software compatibility

• Training and technical support

Perhaps most important, however, is the type of detector on the device. Consider:

• The type and wavelength required (cooled or uncooled, materials, etc.)

• Level of thermal sensitivity (most cameras are sensitive enough for most applications at this point)

• Spatial Resolution (sufficient pixels to generate the picture needed)

Of these three, spatial resolution is the most important, both in terms of cost and image quality. Common resolutions include:

• 160 x 120

• 320 x 240

• 640 x 480

The higher the resolution, the larger and more detailed the picture is going to be. Keep in mind that this growth isn’t linear—it’s exponential. Each step up is going to be significantly more than the last.

Tip: A more sensitive camera will allow you to see more differences in temperature, but that can be controlled with technique as well. For instance, if you put a lot of heat into an object, you can make it show up better on the image. As such, spatial resolution is much more important.

Thermal Infrared Services and Applications

When it comes to maintenance, everyone should have access to an infrared camera, even if it’s a small, cheap one that can be plugged into a smartphone. Thermal imaging can be used in a wide range of maintenance applications, including those described here.

Industries and Machines

Among the many machines where infrared imaging services see use are:

• Incinerators and smoke stacks – Thermal imaging can detect bad refractory, areas that have burned through, and insulation breakdown.

• Mail sorting machines – The temperature of mail going through barcode sorters can impact failure rates for bearings.

• Manufacturing – Any machine that’s built for manufacturing, whether it makes carpet, duct tape, weather stripping, etc., can be inspected with thermal imaging. Hot spots give information on how failures occur.

• Pulp and paper rollers – A lot of energy goes into paper making, and infrared imaging can help maintenance teams make sure the equipment is performing properly.

• Cartridge heating – Due to their shiny surfaces, cartridge heaters need some treatment in order to be analyzed with infrared. The results can be informative.

• CT scanners – Infrared is useful for assessing the tolerances of electrical connections, the impact of higher RPMs, etc. in CT scanners.

• Refractory and kilns – Refractory of all types can be looked at with infrared. It’s easy to find burn holes as well as spots that are close to failing, saving thousands on replacement costs.

• TV towers – Small differences in temperature can indicate failures in wave guides and Klystron tubes.

• Aerostat craft (blimps) – Spots with helium leaks are slightly colder than surrounding areas, making them easy to spot with infrared.

These are just a few examples, of course. Infrared thermal imaging has applications in most—if not all—industries.

Mechanical Applications – Friction

When you rub your hands together, they get warmer due to friction. As mechanical devices wear out, they tend to have more friction between moving parts, and the heat that results from that can be picked up with thermal imaging.

For example, couplings, bearings, and other pivot points are often where failures occur, and the early precursors to those failures are increased friction and heat. As you get a repeatable process down for checking rotating machine components, you’ll be able to plot the temperature over time in your CMMS. As temperatures reach critical levels, it’ll indicate the possibility of a failure.

Tip: When logging temperatures in outdoor environments like sheds, be sure to account for the ambient temperature. The point is to track the increase in heat over time.

Electrical Applications – Resistance

Per the laws written up by Sir James Joule, heat in an electrical system can be calculated based on the current times resistance times time, or:

H = I² x R x T (Heat = Current² x Resistance x Time)

Basically, the more resistance is in a system, the hotter it will get, which is where thermal imaging comes in for electrical systems. If too much resistance occurs in a system, it can heat up and eventually fail.

Infrared can be used at any point in an electrical system, including:

• Generation (such as power plants)

• Transmission (lines and transmission stations)

• Distribution (lines carrying power to everything out in the world, transformer boxes)

Resistance, induction, overloads, and leakage can all cause failure in an electrical system. Common failure points include bushing, ducts, conductors, breakers, fuses, and connection points.

Tip: It’s a good idea to use drones when doing thermal imaging on power lines. If it hits a line, that’s a thousand dollars instead of a human life.

Solar Fields

Infrared is often used in solar fields, both at a module (panel) level and from an elevated view. Hot spots on individual modules indicate problems with specific components. From an aerial view, hot areas might indicate panels that are entirely out of order since they’re not outputting that heat energy to the grid.

Steam Systems and Boilers

When assessing steam traps, boilers, and the like, infrared is a valuable tool. Heated areas—some of which can even show up on surfaces nearby—can indicate leaks from ground level. Elevated views from on top of the building can provide more information on a larger scale since they let you see multiple issues at once.

Combining infrared with ultrasound provides more information since ultrasound will allow you to detect air leaks before pinpointing them with thermal imaging.

Buildings

Problems with buildings can stem from design flaws, construction defects, and poor maintenance, particularly when it comes to heating and air conditioning. Infrared technology lets maintenance teams pinpoint these issues, providing the information needed to make repairs and improvements.

Bad design can easily lead to heat loss during the winter or cold air leaks during the summer, all of which are visible via thermal imaging. Poor insulation, bad seals on windows, leaks from interstitial spaces, and so on are common culprits.

Fact: When it comes to air and heat loss, the most sensitive buildings by far are data centers. In a setting where each asset costs $2 million, it’s important to make sure everything runs reliably and efficiently.

Thermal imaging can be used to find flaws other than AC and heating issues, of course. By introducing some heat into a system, you can find cracks, termite damage, missing concrete and insulation, and even excess moisture (which is particularly helpful for roof moisture surveys).

Tip: As long as you can maintain a high enough spatial resolution, the farther you get from the target with your camera, the more you’re going to see. This is especially important when analyzing entire buildings.

Three Questions to Ask to Determine if an Application Should Be Tried

When figuring out whether a thermal imaging test is going to work for a specific application, ask yourself these three questions:

1. Would the information be valuable to the end user?

2. Is it possible to successfully accomplish the test and get valid results?

3. Would obtaining the information cost more than it’s worth to find out?

You want to make sure you’re using IR tools for purposes that are actually useful to your processes and that they’re worth implementing.

Conclusion

Infrared thermography sees wide usage in many industries, and it’s a vital tool for maintenance technicians to be able to use. Even the simplest cameras can be useful as long as the right methods are used. The data that comes from IR inspections can help maintenance teams anticipate failures and perform preventive repairs when needed.

This article is based on a webinar "Anyone Can Own and Effectively Use Thermal Imaging" with Greg Stockton. To view the recording of the webinar, click this link.