Tantalum Coated Thermowells

Hi,

I have an issue with thermowells in a very corrosive acid steel pickling environment. The main issue I have aside for the extreme corrosive nature of the picking acid is that I need the thermowells to be very responsive. Historically when I used a nickel alloy / Hastelloy thermowell they were very responsive to temperature changes and hence the process ran smoothly however the thermowell would only last few weeks before failing. I tried PTFE lined thermowells and they performed very poorly from a thermal point and were unacceptable. I then switch to a tantalum sheath/cladding for the thermowells and while they survived my acid conditions, they were not very responsive either to the changes in temperature which caused other processing issues. I guessing it was due to the air gap between the tantalum sheath and the steel thermowell as tantalum should be a good thermal conductor. I even tried putting thermally conductive paste between them but the improvement was minor.

So now I am curious about using the Ultramet CPT tantalum process on tapered thermowells and if you believe this will solve both my corrosion and thermal conductivity issues. Looking forwards to your comments.

-Pete

Hello Pete,

You bring up an interesting dynamic that the Ultramet CPT tantalum surfaces are well suited for.

So to get right to your situation, you are right, tantalum is a excellent thermal conductor and should transfer the heat easily, however the air gap caused by the tantalum sheath is an excellent insulator. This is the reason why you are not getting accurate and responsive readings from your thermocouples. So essentially your tantalum sheath is acting like the PTFE coating.

The good news about the Ultra-Metal tantalum surface is:
1) The tantalum diffusion surface is geometry independent, so it will work equally well on straight, stepped or tapered thermowells.
2) It has the corrosion resistance and thermal conductivity of pure tantalum which are both excellent
3) Because we actually grow and diffusion tantalum into the base substrate there is no air gap at all (see Diffusion Surface x-section image link)

So yes it will indeed solve both your corrosion and thermal conductivity issues.

Tantalum Diffusion Surface X-Section