Salt water generators voiding the AGP warranty

[laurieeas]

I read that using a salt water chlorine generator will void the warranty on most above-ground pools. I called Swim N Play yesterday and they concurred. I also called another Canadian company and they too concurred. Are there any AGP manufacturers that allow SWCGs? My husband is very concerned about keeping the pool balanced and likes the idea of salt water, as do I.

[Watermom]

Laurie,
I'm sorry that I can't answer this question for you but hopefully someone will come along soon who can. I just wanted to welcome you to the forum and also say thank you to you for becoming a subscriber. We appreciate the financial support in keeping our forum alive. The Pool Forum helps a lot of people and we are thankful when people help us keep the website up and running which doesn't happen for free! Thanks again and hope you enjoy being a member!

[PoolDoc]

Hi Laurie;

You've got two issues:

1. Will SWCG use void the warranty on your AG pool?
2. Will SWCG use damage or destroy your AG pool?

I don't know the answer to either.

#1 is one you can answer yourself, use the web and your phone. I'd be very grateful if you'd post answers (and links) as you find them. Meanwhile, I'll email PoolSean, and see if he has answers.

#2 is one I'm working on, a bit. It's possible, at least in theory, to protect your pool walls with "sacrificial anodes", like the ones this company
http://www.rotometals.com
sells. But, they are reluctant -- most of their effort is with big ships and military apps, and they aren't convinced that there are that many AG pool owners who'd be interested. So . . . you can help on that one, too.

Do this:
+ after 9am EDT, call "Keith" at Rotometals at 800-779-1102
+ tell him you read on PoolForum.com that he might be able to help you protect your AG pool.
+ he's probably going to say that he's checking in to it.
+ ask him if you can call back in a week.

I've already talked to him, but if you (and a number of others) would call, it would go a long way toward making him think there's a market.

Ben

PS. I'll email Sean as soon as I post this.

rotometals.com 800-772-1102

[Poolsean]

It is also AutoPilot's understanding that most AGP manufacturers with steel walls or rail caps will not warranty their products if there is a salt system installed.

As an alternative, AutoPilot is releasing a low salt (1000 ppm) model, in which AutoPilot will warranty any damage to an AGP, naturally, provided you follow our instructions for operation.
We utilize a special blend of proprietary dry chemicals to establish the 1000 ppm of salinity, and also the correct conditions needed for the chlorine process to work efficiently.

Since we cannot convince the AGP manufacturers that it's not the salinity that is the root cause of the damage, it's still another exclusion to not cover a potential warranty situation. We've had many AGPs operating with salt systems, without damage to the pool. One of which was our former Sales manager, who had his pool working with the Pool Pilot for over 12 years.

[chem geek]

Some, but not all, of the AGP manufacturers use inferior materials. They will corrode faster under conditions of higher electrical conductivity and chloride concentration as is the case with saltwater chlorine generator pools typically using 3000 ppm salt. Most commonly, the problems are seen with inferior stainless steel (or zinc-coated -- i.e. galvanized) screws on some parts such as skimmer openings. However, some people have simply replaced such screws with more appropriate ones and then had no problem. Some examples are here, here (with photos of some rusted bolts here) and here.

Inferior materials are going to have problems even in pools with lower salt levels though will take longer for such problems to develop, but any material "on the edge" can corrode more quickly at higher salt levels. With stainless steel in particular, higher chloride levels interfere with the reformation of the passivity layer so if the material isn't good enough and the chloride level is high enough, then one can inhibit the passivity layer formation faster than it can form at which point one gets runaway corrosion as raw steel becomes exposed. This was discussed previously on this forum such as in this post. Also, when dissimilar metals are used, one can get galvanic corrosion which occurs faster under conditions of higher electrical conductivity (which is very roughly proportional to the salt level as the added sodium chloride salt is the largest component of all ions in the water).

So while the "root cause" may be use of inferior materials, it would be incorrect to imply that the higher salt levels are not a factor. When there is more than one contributing factor, one needs to look at them all together as a system.

[PoolDoc]

I looked at the bolt pictures. The consensus on the TFP thread was that they were zinc plated. However, in another life, I've worked a great deal with stainless components and fastners -- those WERE stainless bolts. However, I learned long ago that much of the stainless used in pool biz is not the 316 or 304 grades I encountered in restaurant service. And, I have personally seen similar SS corrosion on stainless in short periods on non SWCG pools at low pH.

Of course, none of the threads on TFP were more than anecdotal in nature, so it's hard to say what it means, in the absence of a statistical comparison.

I think I need to revise the SWCG FAQ to reflect the warranty issue.

On another topic, did anyone call Keith at Rotometals?

Sean, has Horner ever looked at consulting with a corrosion engineer to work out cathodic protection for AG pools? It would be another product to sell.

Here are wikis for both anodic and cathodic protection:
http://en.wikipedia.org/wiki/Anodic_protection
http://en.wikipedia.org/wiki/Cathodic_protection

It's interesting that you can protect steel by making it EITHER a cathode or an anode in an e-c cell. Keith had said it can be tricky, but I gather for a well-defined system of known surface area and metal mass, it's pretty straightforward . . . IF you know what you are doing.

Ben

[chem geek]

Yes, I think you are right that it's just inferior (low chromium level) stainless steel and not zinc-plated/galvanized. True zinc turns black rather quickly in chlorinated pools (just take a paper clip into pool water to see the effect within a few days).

The warranty issue isn't just regarding AGP's, but also some gas heaters as I list in this post. Now realistically, the number of problems are small, but they are not zero.

I also know that one of the worst commonly used metals in a saltwater pool is aluminum where my own PB has said that "vanishing" pool covers that have headers touching the water require zinc anodes connected to the bonding wire to protect that aluminum from corrosion that he has seen if not protected. Cathodic protection, where you connect a sacrificial anode electrically to the metal you want protected, is very reasonable and generally works well. Anodic protection isn't a general solution since it essentially intentionally corrodes the metal in order to force a passivity layer, but some metals don't form good passivity layers while others do and as noted in the Wiki page, it's quite tricky to get right.

One can also provide cathodic protection by putting a direct negative voltage onto the metal to be protected (say, via a power supply of low DC voltage connected to the bonding wire with the positive end grounded and therefore sacrificed). That's essentially what the sacrificial anodes do -- they convert some metal to ions with the excess electrons providing a negative voltage that makes it harder for the protected metal to corrode, essentially increasing the over-voltage or activation energy hurdle required for such corrosion.

In some extreme cases with salt splash-out (see this post), even cathodic protection with sacrificial anodes would probably not be sufficient since the concentration of salt is simply too great.

And yes, all of these issues occur with lower salt levels as well. It's just that they take longer. Increasing the conductivity of the water by 2-6 times by increasing TDS from 500-1500 to 3000 is going to increase corrosion rates, period. The only question is whether that matters and the answer to that depends on the quality of materials being used and whether there is supplemental protection.

The salt (and chloride for stainless steel) levels vs. the quality of materials or supplemental protection is very similar to chlorine/CYA vs. algae. It is a race or reaction rate competition. In the case of salt vs. corrosion, it is between the factors causing corrosion such as conductivity and chloride ion level (as well as pH and active chlorine level) vs. the factors inhibiting corrosion such as the quality of materials (including passivity layer reformation from stainless steel) or use of cathodic protection. In the case of chlorine/CYA vs. algae, it is between the rate of killing algae from the active chlorine level roughly proportional to the FC/CYA ratio vs. the rate of algae growth that is limited by nutrient levels as well as sunlight and temperature (and type of algae). Just as some chlorinated cyanurate manufacturers say that "CYA doesn't matter", some salt system manufacturers (not Sean) say that "salt doesn't matter". Obviously, both statements are incorrect -- CYA does in fact matter just as salt does in fact matter. Any rational analysis of this situation will not point fingers at a single cause, but will look at these competing factors in order to properly balance them.

[Poolsean]

Ben,

We have not, as a company, experienced enough corrosion damage issues to commit to corrosion studies on AGP, so that is not on engineering radar screen.

In the past, I have suggested rinsing off the bottom and top rails, as these are places where water may collect. As the water evaporates, the salt concentration increases, and will become corrosive due to high levels of salinity. Keep in mind that Sodium Hypochlorite/Bleach usage will also introduce salt to a pool. The same reaction occurs as the water evaporates, yet no one complains of corrosion from the use of bleach. I realize that a salt chlorine generator operates at a higher concentration, the fact is, when the water drips out, and sits on the top cap or bottom rail, whether SCG or bleach, the concentration of salt will be the same as the water evaporates.

Some AGP manufacturers are using resin or polymer top rails, but the bottom rails, which are usually steel or aluminum, should still be occasionally rinsed off.