Thermal Imaging Tanks?

[Brandon Clark]

Anybody ever had a request to do thermal imaging on any sorta tanks?

I assumed that the propane's tanks insulation value and smooth surface would be to reflective to get an accurate image but I assumed wrong.

What types of tanks could benefit from thermal imaging? Are there any services to pursue that involve tanks?

[Matt Schwoegler]

Hi Brandon,

I have a paper that I co-wrote with John Snell a few years back covering this application for thermal imaging. The angle is directed more towards industrial maintenance, but I think you'll find some of the basic principles useful and it should answer a number of questions. You're welcome to download it for free via this link:

http://www.thesnellgroup.com/Receive....aspx?id=10013

All that's required is a quick registration and you'll receive the PDF via e-mail.

Here's the abstract:

Locating Levels in Tanks, Vessels and Silos

This white paper discusses the parameters and limitations that must be addressed when inspecting tanks, shows techniques that can be employed to help locate levels, and provides a number of example images from IR tank inspections.

Hope this helps.

Best Regards,

Matt Schwoegler
The Snell Group
www.thesnellgroup.com

[Brandon Clark]

Originally Posted by Matt Schwoegler

Hi Brandon,

I have a paper that I co-wrote with John Snell a few years back covering this application for thermal imaging. The angle is directed more towards industrial maintenance, but I think you'll find some of the basic principles useful and it should answer a number of questions. You're welcome to download it for free via this link:

http://www.thesnellgroup.com/Receive....aspx?id=10013

All that's required is a quick registration and you'll receive the PDF via e-mail.

Here's the abstract:

Locating Levels in Tanks, Vessels and Silos

This white paper discusses the parameters and limitations that must be addressed when inspecting tanks, shows techniques that can be employed to help locate levels, and provides a number of example images from IR tank inspections.

Hope this helps.

Best Regards,

Matt Schwoegler
The Snell Group
www.thesnellgroup.com

Thanks alot Matt! That's just what I'm looking for. I'm gonna check it out now.

[Scott Gilligan, CMI]

Brandon

Thermal imaging is used frequently now to determine levels inside storage tanks and to confirm actual measurements. Under the proper conditions, you can see air levels, liquid levels, and sludge levels in above ground storage tanks.

The pictures you posted raise several issues when imaging these types of vessels. The area at the bottom of the tank in your pictures is not uniform and there is not a definitive demarcation line. There is also evidence of solar reflections present that I believe you are indicating as the level of contents in the vessel. The other issue encountered when trying to image a vessel such as the ones pictured is that it is a cylinder on it's side. If you remember back to Level I training, imaging helical emitters can be problematic and deceiving depending on your angle. Imaging a vessel such as this will be very hard to obtain accurate levels because of the axis the vessel is installed. Vessels that have their long axis in a vertical orientation are easier to image, however they still have their problems that must be overcome with good imaging technique.

Your images are very nice looking and in good focus, however there is very little usable data that can be derived from them. It never hurts to try new applications and test your abilities with your imager and this is the best way to learn. It is most important to step back and review the images and see what you could be doing different in order to get the results you are looking for. Sometimes it is trial and error, sometimes you just get lucky. Thermal imaging has it's tricks and traps just like normal visible light photography. Sometimes we have to look outside the box to find the answer to the solution.

Keep trying and thinking of ways to use your imager.

[Scott Gilligan, CMI]

One way to get accurate images of liquid levels in a sideways capsule type vessel is to install a strip of high emittance material such as Scotch 191 tape from top to bottom of the tank and let it come to equilibrium with the tank temperature. You can reduce solar and reflected temperatures by imaging at night or by shielding possible reflection sources. The tape can be removed after the inspection and will not effect the painted surfaces to the extent it would be noticeable. Image the tape area and not the shiny tank surface. You should be able to see the level of the liquid petroleum in the tank on your high emittance target.

[David A. Andersen]

Hay Scott I thought you were a Level III thermographer?
Time to change your Sig!?


Brandon, compass orientation and temperatures in transition is important (I am sure that is in the Snell paper).

I see lots of reflection in your scans.
The same effect is visiable on the pump as the tank.
I see signs, utility poles and buildings...
For all you know, the tank is empty or full.
If you can convince yourself to get off that hi-res Rainbow you use all the time, you will likely see more stuff you need to see.

[Brandon Clark]

Thanks to those of you who provided some input. I also don't feel as if my images would be of enough accuracy to feel confident in charging for such services.

There sure seems to be alot of variables involved with pressurized tank imaging as well as alot of stuff that can throw someone off if they aren't familiar with the science behind it. For example, one would think that the lower portion would be the cooler portion as if you were reading the cooler liquid temperatures. Instead the cooler portion shows up as the warmer portion. Matt/Snell's paper states this has more to do with reflectance than emission which basically makes my images useless.

My first thoughts were that I was simply reading the sky's reflection on the upper portion of the tank(mostly true). I can definitely understand what Scott is saying about the benefits of being able to image tanks in the vertical position. The curvature of a horizontal sitting tank offers about the worst conditions available for overcoming reflectance.

The one thing I'm still confused about is if I'm seeing the inner valve stem within the tank. What I'm referring to is the hose sprayer shaped object on the left side of the tank. Every position I took an image from clearly showed this object within the tank. I didn't see any objects around the tank to where I'd be getting that shaped reflection(confirming it's within the tank). Seeing this within the tank was giving me the impression that my liquid levels were a bit accurate.

My only other options are heating and cooling the tank, wrapping some tape around it, or flipping it up into the vertical position and trying to obtain better images. For now I'll continue experimenting with some smaller tanks.

[Scott Gilligan, CMI]

Brandon

If you look at the equation that all thermographers should know you can see where you need to make your adjustments in order to get accurate pictures.

E + R + T = 1.00

Since we would not be concerned about transmittance , this leaves reflectance and emittance as the variables that are influencing how we want to proceed.

The tank surface is highly reflective and has a low emittance value. This in turn will increase our reflectance variable. Now, if we modify the surface to have a higher emittance, this will reduce the reflectance of our tagret. Since the reflective nature is what is preventing obtaining accurate images, it is apparent that this is what we need to overcome.

Modify the tank as I have previously described and you will be able to get the level of liquids inside the tank.

I have looked at your images again and do not know what you are talking about when you say that you can see the valve stem inside the tank. Thermal imagers do not see inside objects because it it not an x-ray machine. You are only viewing the surface temperatures and not penetrating through the surface of the target. What you are probably referring to is a reflection off the tank surface of lines that were nearby.

[David A. Andersen]

You change your angle but you are still looking at half a sphere. No matter where you move to, you're still going to see the same reflections.

Look at the tank valve cover.
The exact same reflections are in that cover!

As I told you already, I can see fences, signs and utility poles all over that tank.

[Brandon Clark]

Originally Posted by dandersen

You change your angle but you are still looking at half a sphere. No matter where you move to, you're still going to see the same reflections.

Look at the tank valve cover.
The exact same reflections are in that cover!

As I told you already, I can see fences, signs and utility poles all over that tank.

Yeah, I agree with you. I'm headed out here in just a few and I'm gonna slap a few strips of black electrical tape on it. I'm gonna swing back by this evening and shoot it again and see if the tape will offer much help.


Here's my next set of thoughts:

I was looking at some other images I took and it seems that the distance from the tank plays the most significant role in accuracy. If I get way way back off a tank than it appears that I'm getting a good image. I don't know the exact distance but as you move away there becomes a point to where you can see almost see 50% of a cylinders surface/curvature. If you can read the heat from nearly 50% of the cylinder than wouldn't that put you at a similar advantage as imaging a vertical cylinder?

It appears that I'm overcoming a huge amount of the reflection by imaging tanks from a far distance. I'm gonna put my telephoto lens on and go across the street and see what kinda image that gives me as well.

You'll notice on the first image that I'm getting alot of reflection because of being close-up. My far off images seem to be getting nice even patterns.

I'm thinking that tape combined with distance will possibly do the trick. Time will tell..

Also, wouldn't most agree that around 20 mins after sunset would be the most optimal time to image a tank with tape on it?

[Peter C. Russell]

Brandon, when you go back take the same picture's but using a different palette for each picture, see if there is a noticeable difference.

[Jason Kaylor]

Another interesting IR phenomena, with rounded shapes, is the appearance of a temperature change around the target. It is more noticeable closer to the "horizon" of rounded targets.

JJ

[David A. Andersen]

Reflectance increases and emissivity changes with angle.

As Scott pointed out:
As p increases, e decreases, t is the same = 1

(p = r) by the way.