Message Board Thread - "Bare process piping & corrosion under insulation"

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Bare process piping & corrosion under insulation Zeri 2/8/2004
I'm using FLIR ThermaCAM.

Q1. Is there a way whereby we can interpret the color variances on the bare process piping into wall thickness(mm)?

Q2. Has there been any study on corrosion under insulation? If any, could someone out there send me the documentation/application concerned?
Re:Bare process piping & corrosion under insulation Doctir bob 2/17/2004
A1. Not directly. If you know the internal temperature of the pipe surface, use your ThermaCam to get the external temperature of the pipe surface, and calculate the heat loss through the surface, you can calculate the thermal conductance of the pipe. With knowledge of the pipe material, you could calculate thickness.

There are several caveats to this procedure. Calculating the heat loss is reasonably straightforward under steady state conditions. I wrote a paper on watt loss calculation that discusses this. I have also written software in Excel that takes input data and performs the calculation.

But I hesitate to push this too hard as the thermal conductivity of metals is quite high. And pipe thickness variations are relatively small. Lateral heat transfer can obliterate small areas of different thicknesses.

Thermographers have had success with detecting coking of process heater pipes, but the coke is much lower thermal conductivity than metal. Thermographers have had little success with finding thickness variations in boiler tubes.
Re:Bare process piping & corrosion under insulation Carlton 3/5/2004
An option worth considering for bare piping - (1) Take a thermal image of a section of pipe. (2) Instantaneously (and evenly) heat the section of pipe using an external heat source such as an high intensity heat lamp. (3) Remove or turn off the heat source and take another thermal image of the section. (4) Subtract the 2 images. The difference probably can be correlated to the wall loss if the piping is thick enough. Good Luck!
Re:Bare process piping & corrosion under insulation Bob Berry 3/5/2004
I have done some pipeline surveys.

If you are trying to survey without removing the insulation then you are going to struggle with this application. If that insulation has an aluminium outer cover then you have no hope.

The survey I done was on a pipeline with very high temperatures and no insulation. There were sections of different thickness and this was obvious in the images. I did not try to evaluate how you could measure this thickness as it was of no interest to my application. I am fairly sure that if there was sufficient data available for the internal temperature of the liquid (in my case) the thickness could be estimated or least some areas highlighted. There are of course a lot of other factors to be taken into consideration.
Re:Bare process piping & corrosion under insulation Michael 12/3/2004
As an alternative, long range UT can be done to inspect long runs of insulated piping. In many applications, this is a very useful and informative solution for insulated piping inspection.

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