Plastic threaded parts for potable water PVC / PE

[Jack Benson]

Hello,

We produce a water heater in France that heats water up to 40 C

we currently use PVC-UH BSPP threaded pieces to act as dielectric connections.

this is an example of the product we use from the French supplier Plasson. There are links to all the technical details:

https://www.plasson.fr/produit/5041-te-a-90-taraude

the max water temp that flows through these PVC-UH parts is 34 C.

We have not had any issues with them not handling the temperature.



I have been looking at other suppliers, as this supplier is not very reliable (currently have to wait until 14/Jan/2024 for a PCS FFF G1/2" threaded Tee as there is no stock)

I have seen there are options such as:
- Polyethylene pipe (PE)
- Polypropylene pipe (PP)

The parts will not be exposed to any UV.

I would like them to be able to handle higher temperatures the the PVC parts we are currently using. The parts we are using are suitable for water up to 45C.

ideally i would like to be able to handle steam (so over 100C but i do not know what it possible with plastic).

thanks for you help

 

[Compositepro]

Threaded connections between plastic and metal components do not tolerate thermo-cycling well due to the high CTE of plastic. Use a dielectric union with rubber gaskets.

 

[TugboatEng]

Why is the plastic necessary? At 1/2" diameter copper pipe is cost competitive with plastic, especially the CPVC you should be using for hot water service.

 

[Jack Benson]

When I join steel & brass fittings there needs to be a material in between that does not conduct electricity to prevent corrosion

PVC fittings are cheap but can only be used at lower temperatures

I was trying to avoid a dielectric union to save cost of it were possible but from the post above is not possible

 

[JohnRBaker]

When I dealt with Plasson, some 30 years ago or so, they were an Israeli company, which started out as a Kibbutz industry manufacturing plumbing for irrigation systems. I met with some of their engineers when they were expanding their business into more commercial and residential lines, still specializing in molded plastic fittings.

Granted, this has nothing to do with answering your question, but I just wanted to make sure that while Plasson probably has a distributor in France, that from what I can see, they're still an Israel-based company.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[TugboatEng]

It's ok to have dissimilar metal junctions. It's the ratio of noble to sacrificial metal that determines the rate of corrosion. For example, it's ok to install a brass valve in a steel pipe. It's not ok to use a steel nipple into a brass heat exchanger.

Otherwise, there is a plethora of hose options that will tolerate your listed conditions and provide galvanic isolation. Look for hose made with EPDM or silicone rubber for longest life.

The tools to utilize the Oetiker clamp system are very affordable. $25 for pliers plus $1 per clamp can have you building reliable hoses.

 

[Jack Benson]

hello all,

yes its the same Plasson from Israel. I googled their head office, but they appear to have local production for local markets.



In the past we have had brass valves on a copper brazed steel 304 heat exchanger and it resulted in the copper in the heat exchanger being corroded.

This image is of a brass threaded nipple screwed into a 304 steel small water tank.

The corrosion is visible.


We have taken the approach to always ensure dissimilar metals do not touch each other, but it is not always convenient.



I would like to be able to attach flexible hoses directly to a steel 304 treaded connection connected to a small water tank (max 45 C), but the tend to have nickel plated brass connectors with a copper insert

This is a mock up of the water tank

I note your point Compositepro and will not use PVC threaded connections where water is hot.


You advice is always appreciated.

 

[TugboatEng]

The brass valves did not cause your heat exchanger to fail. Copper brazed SS heat exchangers are for oil and non-corrosive fluids. You had dissimilar metal corrosion between the stainless steel and copper brazing alloy. If anything, the brass valve delayed the failure some.

Stainless steel adapters from G thread to 37° JIC flare are readily available as are hoses.

 

[0707]

Jack for your case I think you can use teflon pipes or even steel lined teflon pipes acessories at temperatures up to 200ºC.

https://www.gteek.com/ptfe-pipes

regards