In our Level 1 - Thermographic Applications course we endeavor to show as many of the various applications for thermography as we can. We cover the major ones; electrical, mechanical, buildings and roofs, but due to time constraints we can’t talk about every possible scenario wherein thermography can be utilized. One area we do include is storage tank inspections, specifically using the IR imager to determine liquid and in some cases solid levels in tanks.

One of the many hands-on exercises you might recall from Level I is what we call “the cup lab”. It’s actually an exercise in practicing manual Span and Level adjustments. We take three cups, each one partially filled with hot, cold and ambient water, and place them on a table. The object is to adjust Level and Span to highlight the “tank level” in each of the cups. We present this as a preview of tank inspections in addition to honing infrared image adjustment skills. In the cup lab you’re usually able to see the level of water in two of the cups. As you should recall, this isn’t because I can “see through” the cup material, it’s because of the difference in thermal capacitance between the water and the air. The water level in the cup with ambient water in it will be difficult or impossible to see due to the fact that both the water and air are in thermal equilibrium with their surroundings and each other. This is precisely how tank level inspections work as well.

Just to review, when a tank is not completely full, there is air at the top of it. That air changes temperature at a different rate than the liquid does, due to the difference in thermal capacitance between water and air. This results in a difference in the amount of conduction from where the water is in contact with the tank wall compared to where the air is in contact with the tank wall.

We give numerous examples of this application, and in all of them we discuss the material in the tank being a liquid. This may give the impression that this approach only works with liquids, which is not the case.

If any material is placed into a storage tank and there’s a difference in temperature between that material and the surrounding air, it becomes possible to detect the level of the material. It could be grain, thermoplastic pellets, or any material as long as there’s a difference in temperature between the material and the air surrounding it. Just a few weeks ago we had a customer call and request guidance on detecting tank levels in storage vessels for a cement powder. The powder was being placed into the tank directly after going through a drying cycle in its process where it was being heated in a kiln. This made detecting the level quite easy.

So, when working in your applications for storage tanks, don’t discount the value of IR Thermography just because the material in question isn’t a liquid. Give it a shot, you might surprise yourself.