Seal between PEEK and Duplex (other stainless), Titanium

[FC2008]

Hi, I have a pipe section of peek with a bore trough the pipe wall. I'm going to put some kind of penetrator trough that bore. Let's say that the penetrator is made of titanium.

A combination of high temperature and pressure will make the peek very unstable compared to titanium. I have tried with O-rings on the penetrator but they start leaking when the pressure/temperature gets to high.

Are there any good ways of sealing between very different materials as I have?

Thank you.

 

[flexibox]

Did you selectect the correct oring materials in the first place? What is the aplication? Sounds like you have not considered a perfluoroelastomer which has both good chemical and temperature limits.
If pressure is high then you need anti extrusion washers to prevent extrusion.

can you provide ore details?

 

[mecoman]

Hi There,


PEEK does thread very well. If wall is thick enough, you may try a pipe thread connection.

Packing or a valve stem elastomer and compression device. Unsure on your diameters.

Just some quick thoughts.

Cheers,
MECOMAN

 

[scalleke]

I can see the problem here.

A static connection will not work. The elasticity limits of the materials are too dissimilar. Every time a machanical connection is made the Peek will be stressed over the elasticity limit and be deformed. The Peek will also Flow after being tightened so a mechanically tight connection will loosen over time.

Why not try connection with a dynamically sealing O-ring?

How to make it would depend on the dimensions of the Peek pipe.

Why not a flanged connection?

Best Regards.

Scalleke

 

[FC2008]

mecoman: Hi, you say that peek threads very well, interesting! Would you mind explaining why this is so? I apologize for my lack of knowledge

scalleke: You mean by constructing the glands and choosing an o-ring type suitable in dynamic applications?

Thank you all.

 

[mecoman]

Hi FC2008,

Long time since on the site, sorry about the delay.

Exactly why, without my doing research makes my response less on the why and more on the what.

The PEEK material is very stable under 300F. When thread profile cuts very well. The material is very resistant to creep, thus the thread maintains shape.

Using a PEEK with a carbon or glass fiber fill will further increase the strength.

Depending on your wall thickness for thread engagement, you may find sufficient strength. You may also consider using a metric pipe thread. It is a straight thread with an o-ring or flat washer underneath. A shallow counterbore is required for the o-ring to bear against.

We have machined bearing grade PEEK with great repeatability of machine threads with small screws many thousands of times without suffering pullouts.

Talk with the PEEK supplier who is actually forming the material and they should provide additional insight into both machinability and threading capabilities.

It does have the one big weakness, do not try it if 300F or above.

Hope this helps. Sorry about the lack of science, but find myself to the wall with work and opportunities.

Cheers,
MECOMAN