Ok..I'll bite. What does the salt corrode?

[kevreh]

Hmmm..... wonder if this is a "blip on the screen" or a more troubling trend for SWGs. Seems like there's a lot of "if's".... if the right metal/grade, if in the wrong place, ....then rusting might happen. Putting my SS DE filter and new heater at risk is a little concerning. OTOH, I read that the aussies have been using SWGs for years.

Kevin

Yeah, down here corrosion doesn't seem to be a problem. Most of the pools have salinity of 5000-6000ppm, with some operating on seawater and channel water, with the salinity of 17000-22000ppm. The only rare occasions of corrosion of stainless steel are due to electrolytic corrosion. Addition of SWG is usually not the cause of the problem, but merely the trigger.

Wow.... and I was worried I overshot adding too much salt. My ppm is at 3800.

Incidently, for anyone considering a SWG.... I've had my aquarite for 3 weeks now and LOVE the ease of use. Chlorine is consistant, I don't have to lug bleach bottles home, water has never looked better, and no algae whatsoever. The only minor nuisance has been higher PH and ALK (need more muriatic acid).

 

[chem geek]

Re:

Yeah, down here corrosion doesn't seem to be a problem. Most of the pools have salinity of 5000-6000ppm, with some operating on seawater and channel water, with the salinity of 17000-22000ppm. The only rare occasions of corrosion of stainless steel are due to electrolytic corrosion. Addition of SWG is usually not the cause of the problem, but merely the trigger.

Strannik,

Take a look at the "The Trouble With Heaters, Take II" posting at The Pool Biz blog here (you may remember The Pool Guy, TPG, who posted here at one point). Do your pools have gas heaters? If so, what kind of heat exchangers do they use? Are they copper or cupro-nickel or titanium? Do they have U-bends or large radius (circular) bends?

I'm just trying to reconcile the experience seen by The Pool Guy with what you've seen in Australia.

Richard

 

[Strannik]

I'd normally recommend titanium, but people use cupro-nickel as well. As far as the internals go, i've never taken one apart, but judging be the shape of them i'd say mostly u-bends

Have a read through this manual: http://www.hurlcon.com.au/manuals/Jx_heater.pdf
They have a part on prevention of corrosion for their heaters. They do not warranty against heat exchanger corrosion though and they do say 4000ppm max salinity.

We tend to warn our clients upfront about such possibility when we are asked to give advice about installations, so it's very rarely when someone complains about it to us.

And of course installing an SWG right before the heater is a big NO-NO

 

[chem geek]

So my sense is that having introduced salt systems in Australia quite a while ago and having some areas that were salty anyway, y'all figured out how to mitigate salt issues from the get-go so avoided some of the problems seen in some parts of the U.S. where softer stones, exposed bare steel (say, in diving boards), cheaper lower quality stainless steel, and copper heat exchangers are often used. I also suspect this isn't just a salt issue, but one of building and installing products to last vs. building something cheap that doesn't last as long where salt levels can make this planned obsolescence much more obvious.

The manual you linked to basically says that the biggest problem with the SWG is that its automation can lead to higher chlorine levels on overcast days or other situations and that this is the primary problem to faster corrosion. That may be partly true, but the higher salt level itself would lead to higher conductivity that could lead to other forms of metal corrosion.

Richard

 

[Strannik]

in my opinion (and this is my personal belief not backed by any research) all problems started when manufacturing moved to China on a large scale, and companies started to look for ways to reduce costs. goods become cheap, but their lifespan is reduced.

Here is a hypothetical example: in the old days the heater core was made out of copper pipe with 1 mm wall thickness. Now, because of cost cutting, the pipe has 0.5mm or even 0.25 mm wall and copper is of inferior grade.
Will it corrode quicker? Definitely. Is it fault of SWG? I wouldn't say so.

All numbers are fictional of course, but they illustrate my point.

 

[chem geek]

Well, that would explain an overall degradation in lifespan, but not a distinction in that lifespan between SWG and non-SWG pools. It may be that the difference between SWG and non-SWG isn't huge, but when you thin the copper to the point where the failure rate becomes less than 5 years, then even a 50% faster corrosion rate shows up as seemingly very significant (say, 3 year vs. 4 years). If one waited a few years longer, one would then see the non-SWG systems fail as well (on average). Prior to the thinning of the initial copper, the difference between a 15 vs. 20 year life was a moot point since other corrosion or failure factors independent of salt level may have had things fail in the 10-15 year timeframe.

Installations don't put the SWG before the heater; the SWG should always come last. That ensures that the higher chlorine levels and the uneven pH in the flow don't affect the heater. I don't think the higher chlorine levels from unattended pools is the issue, especially with outdoor pools that have CYA in them. This could certainly be an issue for indoor pools that don't typically have CYA. There are certainly a few pools where very high chlorine levels caused problems, but not for most pools.

I've started a more technical thread on copper corrosion here.

Richard