Bond between PU and copper cooling pipes

[drodrig]

Hi there,

We have some cooling pipes where we continuously have leak problems.

Attached a picture to show the setup; A barbed stainless steel nippe - A PU pipe - A barbed copper nipple.

PU pipe has an outer diameter of 10 mm, inner of 8 and length of 55 mm. It goes on the the barbed fittings and we have clamps to tighten it.

We use ethanol at -25ºC (-13ºF) as a coolant. Sometimes when we mount we have leaks but we can solve this by playing with the clamps, the problem is when we cool down (in order to cool down we close the system and we can not see any more). Also we cool, back to room temperature, cool... so this also creates problems.

How can we fix this PU pipe not to have leaks?

We don't need to remove the PU pipe so we could use some permanent fixed solution. In my mind I think about gluing the barbed area with the PU pipe but I am afraid the ethanol will eat the glue.

Thanks
regards,

http://files.engineering.com/getfil...4e4-31305192becd&file=2015-09-21_15.45.46.jpg

http://files.engineering.com/getfil...7f-e7afbb98abb9&file=2015-09-21_15.45.46b.jpg

http://files.engineering.com/getfil...5-d9508790e8f8&file=2015-09-21_15.45.56-1.jpg

http://files.engineering.com/getfile.aspx?folder=b871a1b3-24cd-44ba-9a5d-3c3b26cf248c&file=Pipes.png

 

[Compositepro]

You have to use spring energized tube clamps that can move with the PU tubing as it expands and contracts. The worm gear clamps you are using will not move, so the PU will yield when it heats-up. Then it leaks when it cools. Another alternative is to use o-ring sealed tube fittings.

 

[bimr]

Consider replacing the fittings with Swagelok fittings.

https://www.swagelok.com/downloads/webcatalogs/en/MS-13-03.PDF

 

[LittleInch]

What is the OD of the two tubes?

do you have a diagram or photo of the "barbs"

Some form of factory fitted braided hose with metal screw connectors would seem better than this rather homemade looking affair.

You're right to question the solubility of any glue.

A little search shows that the minimum temperature for PU varies quite a lot. -25C is quite low and the PU you're using could jst become quite brittle and hard and unable to cope with any vibration.

Why is this flexible coupling here? what level of forces does it have or vibration?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

There are push-lock fittings with internal o-rings which will work better than Swagelok for OD sealing on PU tubing (you have tubing, not pipe).

Example is Legris, but there are other brands (just like Swagelok is not the only competent mfg of OD comp fittings)

Make sure the o rings are good for cold and with ethanol. Otherwise, Swagelok, but with an ID insert to give the ferrules something to deform against- same as is required when using PVC tubing with OD compression fittings.

 

[drodrig]

Compositepro, I didn't know about these spring hose clamps, I talked to the guy in the maintenance workshop, they don't have but I am looking for them.

Bimr, in a first look it seems Swagelok fittings are too long, we only have 55mm and we need two of them (copper-PU and PU-SS), I'll check in detail

LittleInch, stainless steel and copper have an OD of 8, this is also the inner of the PU. I don't have a photo of the open system, but look like something like this:

http://www.brewshop.co.nz/media/cat...8d6e5fb8d27136e95/n/i/nipple-1-2-barb-3-8.jpg

The clamps go at the base of the fittings (not right on the barbed part)

The problem about metal fittings on the plastic pipe is again the space.

We use these PU pipe in order to insulate electrically the system. The system is static and there are no vibrations. Also we need something flexible which can bend in order to mount it.

Moltenmetal, Legris looks promising, I'll dive in their catalogue deeper

thanks all!

 

[Compositepro]

Keep in mind some basic principles of hose and barbed fittings. Hoses are usually made with a braided construction, which will neck down when stretched and expand if axially compressed. The braided construction is what makes the hose flexible.
If you clamp the hose on the non-barbed part of the fitting then fluid pressure will tend to expand the tube and lift it off the barbs. Then the seal will be solely due to hose clamp pressure on the smooth part of the fitting. This effect is counteracted by the pressure also tending to stretch the hose axially. If your fittings are fixed in location then there is no stretch due to pressure.

 

[drodrig]

ahá,
so we have to put the clamps on the barbed section
good to know!
thanks

 

[LittleInch]

Never used it but try this stuff as well...

http://www.gasoila.com/products/pipe-thread-sealants/gasoila-e-seal-thread-sealant.html

Claims to be ethanol resistant.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Regarding "we only have 55mm".

One would think that you would be able to make a pipe loop so that your best option would fit easier.

Maybe it would help if the connection had more flexibility in it.

 

[drodrig]

Interesting option the Gasoila, but it seems it's more for threads, I'll see if I can get it here, in Germany.

About the loop we don't have space, but I have ordered from Legris (Parker) some Push-In fittings

Thank you everybody