Stainless steel pipe for swimming pool water? 1

[BronYrAur]

I know that chlorine attacks stainless steel, but I see stainless steel ladders, etc in swimming pools. So I am confused.

I will be installing a steam/water heat exchanger to heat pool water. The heat exchanger will be cupro-nickel and I will be piping the pool water in PVC. My concern is the pool water piping connection right at the heat exchanger. I am thinking if the steam valve failed and the unit overheated, the PVC pipe will melt. So I was going to run a short distance of stainless steel pipe from the heat exchanger and then transition to PVC. i can't seem to find any literature or examples where this has been done. Is it OK to use stainless piping? Any other suggestions? thank you.

 

[EdStainless]

There are a few very high alloy SS grades used in pool water application such as AL-6XN or SeaCure.
But far more common is Ti. the grade 2 commercially pure stuff is fine in this service.
It is what the heat exchangers are usually built from.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[BronYrAur]

Thank you EdStainless. I'm not familiar with that material. Would you use 316 stainless steel pipe?

 

[georgeverghese]

This may help also. Doubt you'll get much life out of a CuNi HX in chloride / chloroamine laden, warm - hot pool water.

https://www.assda.asn.au/blog/352-stainless-steel-for-indoor-swimming-pools

 

[TugboatEng]

Do not combine SS piping with CuNi. The CuNi is very galvanically sacrificial to the stainless and you will experience erosion in the immediate vicinity of the connections.

CPVC should be used for hot water. CPVC can operate at the boiling temperature of non-pressurized water. There are many rubber hose products that can greatly exceed that temperature. You should consider a protective device that will prevent scalding water from being pumped into the pool.

 

[moideen]

I'm thinking about the copper/nickel heat exchanger, which is easy to break because chlorine is an easy way to hit your HX. Because of these problems, most makers won't offer a warranty for more than one year. From what I've seen, a lot of copper-nickel heat exchangers break within a year. So, when looking for new pool heat pumps, a titanium heat exchanger is an important feature to look for.

The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-

 

[TugboatEng]

This document states that chlorination has little impact on the corrosion of 90/10 and 70/30 copper nickel alloys.

https://www.copper.org/applications/marine/cuni/pdf/Eurocorr-2011-4882-Grolleau.pdf

Perhaps the wear of CuNi heat exchangers is influenced by other factors. For higher temperature services 70/30 is mandatory.

 

[EdStainless]

The high temperatures, the great variation in chlorination levels, and the presence of organic chloramines are very rough on CuNi.
I'll second the warning to not connect any SS to CuNi.
No, 316 will not work in this service.
Run the CuNi as far as you need to and then connect to CPVC rated for the temperature.
Likely in a couple of years you will be replacing this a Ti unit anyway.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[pierreick]

HI,
What about U45N?
Pierre

 

[Krausen]

I'm thinking about the copper/nickel heat exchanger, which is easy to break because chlorine is an easy way to hit your HX. Because of these problems, most makers won't offer a warranty for more than one year. From what I've seen, a lot of copper-nickel heat exchangers break within a year. So, when looking for new pool heat pumps, a titanium heat exchanger is an important feature to look for.

I have no professional experience in this area, but I believe you’re line of thinking is correct here. I bought a house with a swimming pool fired heater that featured a 70/30 Cupronickel coil. Original owner had piped his chlorine injection upstream of this heater coil (instead of downstream of coil, as required by heater manufacturer). When I started the pool system my first year, the 1 yr old heating coil leaked immediately. From the chlorine exposure. I replaced the coil & repiped the chlorine injection to downstream of the heater. Haven’t had a problem with it in 3 yrs now.

 

[EdStainless]

Krausen, You are right on, the CuNi will handle 0.5ppm Cl, but not the spikes that you see at injection.
The reason that people use Ti for the heaters is that it is easy to work with and no more expensive than high alloy SS grades.
Aloys like U45N or 2205 will not handle this service.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed