Replace failed PTFE liner with Tantaline for liquid bromine?

[HBMetals]

Hi engineers,we are trying to replace several PTFE lined steel pipes for a liquid bromine line. Pressure rating: 0.2 MPa, Temperature: room/ambient. Please see the attached 3 photos: the flanged steel pipes are lined with PTFE. A small hole was drilled on each end of the pipe to supervising possible leakage. Small bubbles were found on each hole which indicated leakage. It seems that bromine completely diffused through the PTFE liner. Some engineers recommend us to adopt Tantaline which will be more costly. Some others tell us that PTFE is suitable for bromine application, however, the failed PTFE is produced in too bad quality. Can I get some advice here? Thank you.

www.metalspiping.com

 

[HBMetals]

Another Photo.

www.metalspiping.com

 

[moltenmetal]

PTFE is suitable for bromine but permeation is something you have to deal with.

PFA is more resistant to permeation than PFA and is something you should consider.

Permeation of halogens or halogen acids through PTFE etc. typically results in the permeation of dry gas, which can be either collected in a scrubber or safely vented by means of a coupling over the weep hole which is fitted with a sacrificial stainless steel pipe nipple. Corrosion tends to occur where the dry permeate re-combines with atmospheric moisture.

Tantaline is a 0.002" thick layer of tantalum metal. Tantalum is resistant to bromine, but a 0.002" thick coating of anything may eventually be abraded away or otherwise damaged. That could be a big or a small worry for you depending on your service. In comparison, a 0.015" thick solid tantalum cladding liner inside pipe and fittings can also be used. It is even more expensive than Tantalining and far, far more expensive than PFA-lined carbon steel pipe and fittings, but it is obviously more robust against erosion etc.

 

[moltenmetal]

Your construction of your PTFE-lined spool is incorrect for this service: that weep hole needs a threaded coupling welded around it as noted above, or else corrosion of the steel from the outside inward is inevitable.

Regrettably, welding anything to a lined pipe after it has been lined is likely going to damage the liner regardless of how careful you are. So my suggestion would be to replace the line with a PFA-lined pipe constructed with proper weep holes with weep couplings and sacrificial nipples as noted in my message above.

 

[HBMetals]

Thank you for your advice. I will forward your message to our engineer.

BEST

http://www.metalspiping.com

 

[WKTaylor]

See following Tables [a few of many] for chemical resistance of various plastics types...

http://www.plasticsintl.com/plastics_chemical_resistence_chart.html

https://www.usplastic.com/catalog/files/charts/LG CC.pdf

http://sevierlab.vet.cornell.edu/resources/Chemical-Resistance-Chart-Detail.pdf

Perhaps the real problem is the bond between the PTFE and the steel pipe...

What about another pipe alloy, such as Inconel?

Regards, Wil Taylor

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[moltenmetal]

Dry liquid bromine can be handled in carbon steel- in fact that's how it's shipped.

Opinions vary, but in my view you don't actually want a "bond" between the teflon and the carbon steel per se- permeation is going to happen and you want a vent path for it to the atmosphere so that it doesn't cause the liner to bubble inward.

 

[HBMetals]

Thank you, WKTaylor & moltenmetal.