Infrared: A Thermal Monitoring Guide
by Rich Shannon, Director/Co-Owner of Viper Imaging
For those of you working in the oil and gas, paper and pulp, steel, and power generation industries, you might be lying awake at night worrying about whether or not something catastrophic was to happen at your facility. What if a faulty electrical connection shut down a critical piece of equipment – or even your entire plant? What if the tubes in your furnace get too clogged with slag? What if you were to have a dangerous release of certain types of gases? Or, one of the many combustible materials in your plant could catch fire and destroy valuable equipment, not to mention putting the lives of your team at risk?
The solution to this ongoing worry is a robust thermal monitoring system that will alert you to these scenarios in plenty of time to remediate. But if you’re patching together your own thermal monitoring solutions in-house rather than trusting the monitoring to a well-versed expert in the field (like Viper), you might not be aware of the full picture of how to properly manage and detect all of the various scenarios that could go wrong.
With that in mind, we wanted to educate you on the finer details of using different wavelengths of infrared for thermal detection, which provides multiple ways to detect problems in and with various materials, vessels, and machines (let’s refer to them as “targets”). “Forewarned is forearmed” as they say, and the way to better understand your potential risk for problems is to better understand the purpose of various wavelengths along the electromagnetic spectrum, and how to choose between short, mid, or long-wave infrared thermal camera systems.
Short, mid, or long-wavelength infrared detection: which is best?
As you may have surmised, there is no one wavelength that will properly alert you to all the potential problems in your facility. Different wavelengths detect different types of problems, and it’s likely you need a combination of short, mid, and long-wavelength infrared detection systems for different areas of your plant. So let’s compare and contrast the different wavelengths, what they detect, and when to use them.
First, an electromagnetic spectrum primer
Infrared is part of the electromagnetic spectrum that falls after gamma rays, x-rays, ultraviolet, and visual light. It’s in the infrared wavelength where detection can happen that humans can’t see with the naked eye – but thermal imaging cameras can. Infrared allows you to detect certain emitted energies and permits you to detect problems before they occur. Understanding which part of the infrared spectrum detects your areas of concern is vital to properly developing a detection safety strategy.
When thinking about thermal detection, since we are not actually making physical contact with our target, we are measuring our target in a non-contact method by measuring the radiated energy of an object. After all, all objects emit infrared radiation. However, they emit at different levels. This is called Emissivity. To get the most accurate reading, we want the Emissivity to be at its highest. That gives us the most accurate and repeatable way of making this measurement. So, there are optimal Spectral Ranges for objects where they emit energy at their highest, measured in microns.
It’s also critically important to understand the wavelength range of each of the materials you produce or use as raw materials, in order to best understand the type of thermal monitoring system you need in order to get the best results.
The short wavelength band
Short wave in Infrared (or SWIR) is nominally around .7 to 2.5 microns. In general, metals will emit the most energy at the shortest waveband, so when temperature measurement is very critical, we try to use short-wave thermal imaging cameras. Short-wave sensors are less sensitive to variations in changes in emissivity. Steel is a perfect example of this. If you are in a steel mill, and for instance are trying to measure at the Caster, you will be less affected by different surface conditions, or changes in different alloys that might be present.
The mid-wavelength band can detect emissions roughly in the 3-5 micron range. An important wavelength in the mid-wave is 3.9 microns which can “look through a clean flame” inside furnaces and boilers. One such use of mid-wavelength infrared detection is in the case of a power plant burning coal for power. The challenge for coal-burning power plants is a build-up of slag in furnace tubes, which causes inefficient energy production. In some instances, this slag buildup can become huge – sometimes larger than the size of a car – and could cause major damage if knocked loose by a soot blower. Since plant personnel shouldn’t operate soot blowers all the time (because they are very high-pressure and could even blow holes in the furnace tubes themselves), mid-wavelength infrared detection cameras that can alert when there is excessive slag buildup is a much more efficient approach to furnace tube maintenance.
Examples of materials falling in the mid-wave infrared band include Flame Filters (3.9 microns), glass (4.8 to 5.2 microns), and thin-film plastics (3.43 microns.)
Long-wave band thermal imaging cameras can detect objects in the 8-14 micron range. Long-wave thermal cameras can actually see through smoke and some steam, whereas short and medium-wave cannot. It may not be as precise for monitoring materials in an exact micron range, but if it can see the target better, it’s more appropriate for certain types of measurements. Longwave cameras are often used outdoors as well because they are less affected by solar reflections – making them a great choice when monitoring inside substations or power lines.
It’s true: No “one size fits all” with thermal monitoring systems for industrial applications
We think you can see why when Viper Imaging is invited to make a proposal for hazard protection, we thoroughly assess all materials and areas of concern before making very precise recommendations on the types of thermal detection solution required for each area of a client’s plant or facility. Unfortunately, sometimes even the smartest, most well-intentioned engineer tries to standardize their approach to hazard detection internally, using imaging solutions with the same infrared band wavelength for all their applications, often with poor results. At Viper, we have decades of experience understanding our customers’ applications and how to properly apply infrared sensors in the correct manner.