Saltwater Pool heat exchanger fittings

SpeyFitter · April 2020

Hello Ladies & Gentlemen,

Been a while - got a titanium pool heat exchanger Ill be likely installing in the somewhat near future on a wall mount boiler to heat a saltwater pool. Its an all metal fully welded titanium exchanger. I know the exchanger is the critical part in the grand scheme, however my concern is the fittings on the saltwater pool side that connect it to the plastic. For those not aware my experience is based on conversations with technical people at IPEX and some experience as a result of those conversations in that connecting metal to PVC/plastic via a threaded connection is always best done with a male metal pipe MIP nipple/thread and a female pre-stressed plastic FIP adapter (with the metal ring). This is over screwing a plastic MIP into a metal FIP which can suffer overtime due to the differing expansion rates of the metal vs plastic overtime (never mind screwing a metal MIP into a plastic FIP without any metal reinforcement ring or pre stressing of the plastic). This is also beneficial for sensor wells on pool piping where you have a male/MIP well thread and when you use the pre-stressed plastic FIP's with the metal ring it reduces the likelihood overtime of leaks/issues/cracks. My principal concern is since the Titanium pool HE has female fittings on the pool side, while I know stainless pipe nipples will likely hold up a good while against the saltwater (and I know the importance of introducing saltwater downstream of the HE where possible), I was wondering if anyone had any luck sourcing either Titanium or Cupronickel Pipe nipples which I am told and from research will stand up better to salt water than stainless. I recognize they may be more expensive, especially in 1 1/2" size but it's only two nipples so.......or should I just use stainless nipples?

EBEBRATT-Ed · April 2020

I have no experience on salt water. The best way to connect plastic to metal is with flanges but you method also works

pecmsg · April 2020

Plastic to anything........pipe dope, NO Teflon.

I also prefer Flanges.

hot_rod · April 2020

Maybe source some 316TI nipples the titanium alloy looks like the best SS grade. Then Fernco from that nipple to Sch 80 to plastic to avoid any other threaded connections.

If you have access to PP fusing equipment, maybe that is the best plastic option? AquaTherm or others.

https://www.ganpatind.com/stainless-steel-316ti-nipple-supplier-exporter/

PerryHolzman · April 2020

The issue you need to be aware of is galvanic corrosion of the fittings that screw onto the Titanium.

None of the 300 or 400 series SS are recommended for direct contact with the Titanium because they have both an "Active" and "Passive" phase, which are far enough apart that under the right situation these metals can galvanically corrode within themselves (different metal grains become Active and other grains become Passive - not real common; but, I've seen it and its in the literature).

You cannot normally control if say a 304 or a 316 SS will be in its active or passive stage, and the metal grains can switch while in service if certain things are spilled on them.

Here is a good galvanic reference chart:

https://structx.com/Material_Properties_001.html

I once spent in the range of $20,000+ while working at a nuclear power plant to perform specific galvanic testing of various materials to figure out how to build heat exchanges without galvanic problems with highly Nobal materials that were close to titanium on the galvanic charts after our plant had a series of HXs with massive galvanic corrosion issues after being retubed with "SeaCure" tubing.

2205 Duplex SS was the intermediate material that worked; and that is what you should be looking for. It also appears that Alloy 20 SS is also available and suitable as well.

Both materials are regularly available in plates, pipes, pipe fittings and flanges, and tubes. I am sure there are tube fittings that match (although they might be a slightly different alloy as they would need to be harder than the tube).

If you are having difficulty finding tube fittings for your application. Put a 2205 Duplex SS or Ally 20 SS pipe fitting (coupling, bushing, nipple, etc.) between the Titanium and a 316 SS fitting.

I wish you well with this,

Perry

Intplm. · February 12

@SpeyFitter

Viega has a line of specialty fittings that should work nicely with the applications you are working with.
I would look into them as well.

realliveplumber · February 12

All pools that utilize chlorine to sanitize the water will become, or are "salt water" pools.

after the chlorine is consumed, it leaves behind salt that will accumulate in the water.

Most salt water chlorine generators require 3000-3500 ppm. of salt to function.

A typical pool, without large, regular water exchanges, reaches that threshold in in about 2-3 years.

[the ocean is about 35,000 ppm. ]

We use Shc 80 CPVC for pool piping.

they make female adaptors that have a stainless steel reinforcing band. or put a hose clamp on it.

Jamie Hall · February 12

Wander over to your local shipyard or marine chandler and see what they are doing... they have some experience with salt water.

Shore_heat2 · February 17

I did one with a titanium heat exchanger it wasn't a pool but a koi pond his first exchanger was stainless and it rotted internally within about 7 years. I was having trouble finding the fittings to transition so I used shielded dwv couplings to transition to PVC. It worked great for many years no leaks.

Saltwater Pool heat exchanger fittings

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