Joining Titanium tubes to teflon tubesheet.

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    Titanium Welding
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Discussion Overview

The discussion revolves around the challenges and options for joining titanium heat exchanger tubes to a PTFE (Teflon) tubesheet. It explores design considerations, material compatibility, and potential alternatives in the context of a heat exchanger application involving corrosive fluids and specific pressure conditions.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions the reasonableness of using a titanium tubesheet due to cost concerns, suggesting alternatives like titanium clad stainless tubesheets or stainless steel tubesheets with epoxy coatings.
  • Another participant inquires about the pressure and type of fluid in contact with the Teflon, emphasizing the need for clarity on these parameters.
  • Details are provided about the operational conditions, including a maximum tubeside pressure of 2 barg and steam on the shell side at the same pressure, with the Teflon tubesheet in contact with both steam and a saturated salt solution.
  • There is a discussion about the potential need for additional support for the Teflon due to creep at elevated temperatures, with suggestions for using packed glands or considering alternative configurations like running process tubing as sleeves through a longer tube shell.
  • One participant expresses concern that moving to a different configuration may not resolve the underlying issues related to the tube sheet.
  • A later reply suggests that if cost is a significant constraint, using a steam jacket around the titanium tubing could be a viable alternative, moving away from the tube and shell configuration altogether.

Areas of Agreement / Disagreement

Participants express various concerns and suggestions regarding the design and materials, but no consensus is reached on the best approach or solution. Multiple competing views remain on how to effectively join the titanium tubes to the Teflon tubesheet.

Contextual Notes

The discussion highlights uncertainties regarding the joining methods and the implications of using different materials under specific operational conditions. Limitations include the potential for creep in Teflon at high temperatures and the cost implications of various design choices.

rollingstein
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What would be the possible options to join Titanium Heat Exchanger tubes to a PTFE / Teflon tubesheet? These are 38 mm tubes, 2 mm thick. 6 m total length. Seamless tubes.

Is this a reasonable design decision? Full titanium tubesheet would be excessively expensive & isn't needed since only the tube-side fluid needs Ti because of corrosive nature.

The other options might be Ti clad Stainless tubesheets or an SS tubesheet with an epoxy coating. But not sure if joining those to Titanium tubes is any easier?
 
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What sort of pressure, and what sort of fluid in contact with the teflon?
 
Bystander said:
What sort of pressure, and what sort of fluid in contact with the teflon?

Tubeside pressure 2 barg max. Shellside is steam at 2 barg max. i.e. 135 C.

The teflon tubesheet will contact steam on one side & on the other a saturated salt (NaCl / Na2SO4) solution at approx. 105 C.

The high chloride conc. & high T motivate Titanium tubes. The unit is fairly small capacity, approx. 20 m2.

PS. If you'd suggest any alternative design decisions, I'd love to hear.
 
Unknown in Ti. Two barg steam in the shell. Close the shell with Teflon. Saturated brine other side of tube sheet from shell --- also at 2 barg?
 
Bystander said:
Unknown in Ti. Two barg steam in the shell. Close the shell with Teflon. Saturated brine other side of tube sheet from shell --- also at 2 barg?

Yes. Both sides at 2 barg.

Hot NaCl brine on tube side.
Steam on shell side.

PS. Did I misunderstand what you asked for?
 
rollingstein said:
The teflon tubesheet will contact steam on one side & on the other a saturated salt (NaCl / Na2SO4) solution at approx. 105 C.
I keep hearing you say you're separating three streams from one another, and Teflon is a working seal between two of them.
 
Bystander said:
I keep hearing you say you're separating three streams from one another, and Teflon is a working seal between two of them.

Ok, sorry. That's not what I meant. There's only two streams.

Perhaps this diagram clarifies things:

V8IrK45.jpg
 
Okay, so the Teflon is dealing with steam pressure versus atmosphere. You are going to have to support it with some sort of plate, in which case you might want to look at packed glands through a plate. That kicks expenses up, but the creep rate for Teflon at that temperature is going to be an endless headache. Can you just run the process tubing as sleeves through a longer tube shell? Or, is that too much loss in heat transfer efficiency?Edit:

And, this does nothing but move the problem --- you've still got to come up with something for a tube sheet.

Second Edit:

Actually if the Ti cost is the constraint, steam jacket that length of Ti tubing, and forget the tube and shell configuration.
 
Last edited:

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